Available via license: CC BY 4.0
Content may be subject to copyright.
Citation: Berrocal, D.I.;
Blandon Rodriguez, J.;
Ortega Del Rosario, M.D.L.A.;
Harris, I.; James Rivas, A.M. Heat
Transfer Enhancements Assessment in
Hot Water Generation with Phase
Change Materials (PCMs): A Review.
Energies 2024,17, 2350. https://
doi.org/10.3390/en17102350
Academic Editor: Antonio Lecuona
Received: 31 March 2024
Revised: 5 May 2024
Accepted: 10 May 2024
Published: 13 May 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
energies
Review
Heat Transfer Enhancements Assessment in Hot Water
Generation with Phase Change Materials (PCMs): A Review
Diana Isabel Berrocal 1,2 , Juan Blandon Rodriguez 1, 2, * , Maria De Los Angeles Ortega Del Rosario 1,2,3,4 ,
Itamar Harris 1,5 and Arthur M. James Rivas 1,3
1Research Group—Iniciativa de Integración de Tecnologías para el Desarrollo de Soluciones
Ingenieriles (I2TEDSI), Faculty of Mechanical Engineering, Universidad Tecnológica de Panamá, El Dorado,
Panama City 0819-07289, Panama; diana.berrocal@utp.ac.pa (D.I.B.);
maria.ortega@utp.ac.pa (M.D.L.A.O.D.R.); itamar.harris@utp.ac.pa (I.H.); arthur.james@utp.ac.pa (A.M.J.R.)
2Research Group in Design, Manufacturing and Materials (DM+M), Faculty of Mechanical Engineering,
Universidad Tecnológica de Panamá, Panama City 0819-07289, Panama
3Sistema Nacional de Investigación (SNI), Clayton, City of Knowledge Edf. 205,
Panama City 0816-02852, Panama
4Centro de Estudios Multidisciplinarios en Ciencias, Ingeniería y Tecnología (CEMCIT-AIP),
Panama City 0819-07289, Panama
5Department of Mechanical and Materials Engineering, Worcester Polytechnic Institute,
Worcester, MA 01609-2280, USA
*Correspondence: juan.blandon@utp.ac.pa
Abstract: The utilization of phase change materials (PCMs) in solar water heating systems (SWHS)
has undergone notable advancements, driven by a rising demand for systems delivering superior
performance and efficiency. Extensive research suggests that enhancing heat transfer (HTE) in storage
systems is crucial for achieving these improvements. This review employs a bibliometric analysis
to track the evolution of HTE methods within this field. While current literature underscores the
necessity for further exploration into hot water generation applications, several methodologies
exhibit significant promise. Particularly, strategies such as fins, encapsulation, and porous media
emerge as prominent HTE techniques, alongside nanofluids, which hold the potential for augmenting
solar water heating systems. This review also identifies numerous unexplored techniques awaiting
investigation, aiming to pave new paths in research and application within the field of hot water
generation. It highlights methods that could be used independently or alongside predominantly
used techniques.
Keywords: phase change material; heat transfer enhancement; domestic hot water; TES; solar energy
1. Introduction
The escalating effects of climate change and expanding populations fuel a greater need
for building energy. This underscores the urgency of transitioning to cleaner energy sources
to diminish dependence on fossil fuels, especially for vital requirements like heating water.
Solar energy offers a sustainable solution to decrease conventional energy consumption,
cut costs, and mitigate greenhouse gas emissions [
1
–
3
]. Despite the promising strides
in solar energy applications, challenges persist, including intermittency, lower thermal
efficiency compared to conventional sources, and temporal imbalances [
4
]. Addressing
these hurdles requires tapping into the energy storage capabilities of specific materials to
guarantee availability when required [5].
The literature discusses various heat storage methods: latent heat thermal storage
(LHTS), sensible heat thermal storage (SHTS), and thermochemical heat thermal storage
(THTS). LHTS involves a phase change of a material within a specified temperature range
to store and release energy for tailored thermal applications. SHTS stores thermal energy in
a material, maintaining its physical state, with energy correlated to temperature, quantity,
Energies 2024,17, 2350. https://doi.org/10.3390/en17102350 https://www.mdpi.com/journal/energies
Energies 2024,17, 2350 2 of 35
and specific heat changes. THTS employs reversible physicochemical reactions for thermal
energy storage (TES) and release [
6
,
7
]. Compared with SHTS, LHTS can be smaller, which is
a significant advantage for use in domestic or residential areas [
8
–
10
]. It also allows energy
to be recovered at a constant temperature [
11
]. Furthermore, several authors [
6
,
12
–
15
] have
shown that integrating both SHTS and LHTS can reduce costs, enhance efficiency, minimize
temperature drops, improve heat transfer, and decrease storage space requirements.
Over the years, significant advancements have been made in LHTS, especially with
the integration of solar energy, which has proven highly effective in providing clean
energy for various applications [
16
–
19
]. LHTS can employ phase change materials (PCMs),
which absorb and release energy during phase transitions. These PCMs are categorized
into three types: solid–liquid, solid–gas, and liquid–gas. Solid–liquid PCMs, particularly
organic PCMs like paraffin, are most commonly used for hot water generation due to
their suitability for low-temperature applications [
10
,
20
–
22
]. Organic PCMs (paraffins
and fatty acids) exhibit extended operating lifespans, enduring thousands of freeze/melt
cycles [
23
–
25
]. Paraffins, in particular, can maintain their functionality for up to 30 years
without degradation [
26
,
27
]. For hot water generation, PCMs with a melting temperature
range of 50 to 60
◦
C are recommended to ensure optimal efficiency and performance [
28
].
The application of PCMs in water heating has been documented since 2003, experiencing a
notable increase in research and implementation between 2018 and 2022 [29,30].
PCMs provide significant benefits, including a high energy storage capacity, decreased
corrosion, and thermal stability [
8
,
31
–
33
], making them highly suitable for hot water gen-
eration systems (HWGS). Such systems experience enhanced efficiency and prolonged
operational periods [
34
,
35
]. At present, there are patents for TES [
36
], SWHS [
37
], and
also for integrating PCM into aforementioned systems [
38
–
40
]. SWHS typically comprises
three key components: the solar collector, storage tank (optional in some systems), and
heat transfer fluid (HTF—with good thermal conductivity) [
41
]. HTF serves as a medium
for energy transfer in heat exchange systems, whether PCM is employed or not [
42
,
43
].
Typically used in hot water generation, HTF, such as water [
44
], facilitates human con-
sumption in various applications [
45
]. PCMs demonstrate efficient heat transfer during
their molten phase, primarily facilitated by natural convection. However, as they solidify,
due to their low thermal conductivity, a reduced heat transfer and performance between
the PCM and the HTF is shown [
3
,
46
]. Consequently, charging and discharging times are
prolonged, and the energy storage and release capacity of PCMs are reduced [
22
,
33
,
47
,
48
].
Lastly, convective boundary conditions in heat transfer occur due to forced convection
from/to the HTF, allowing energy release or absorption [
33
]. Researchers have developed
various techniques to enhance the heat transfer system between PCM and HTF in TES
systems [
22
,
49
]. These include improving PCM properties, optimizing collector design for
better heat transfer, enhancing HTF, and incorporating larger surfaces [13,50–53].
Harris et al. [
16
] emphasize that improving heat transfer in water solar heaters (WSH)
with PCM presents a promising avenue for research, supported by numerous studies
confirming its efficacy in achieving system autonomy. Furthermore, the authors suggest
expanding this research to encompass investigations into diverse climatic conditions, eco-
nomic implications, and health considerations related to heat transfer enhancements (HTEs)
or PCMs. A growing body of research is dedicated to finding innovative ways to store more
energy in less time using PCMs alongside other materials and techniques like nanoparticles
and fins [
54
–
57
]. Some of these HTEs involve integrating various methods to enhance
efficiency and storage capacity while reducing the duration of charging and discharging
periods [
12
,
22
] or using PCM encapsulation to increase the stratification capacity of a
TES tank and have hot water available for longer. This is achieved as the temperature
difference between the HTF and PCM increases [
58
]. There are various patents on HTE,
including encapsulation [
59
], porous media [
60
], coils [
61
], and nanoparticles [
62
]. This
research exclusively concentrates on the advancements in LHTS and explores potential
enhancements that can be implemented in this type of storage.
Energies 2024,17, 2350 3 of 35
This paper presents a comprehensive review and bibliometric analysis of HTEs appli-
cable to HWGS using PCMs or other HTFs. Previous literature reviews have demonstrated
significant progress in various HTE methods across different applications, including those
relevant to this study. However, this new review offers a more focused approach, highlight-
ing the most commonly used techniques and those with potential for future research in this
field. As such, our analysis categorizes advancements into three primary groups, active,
passive, and hybrid methods employing PCMs, while also exploring the use of nanofluids
in solar collectors as an innovative heat storage solution. The main objective is to chart a
course for HTEs that have seen widespread use or potential for future application in HWGS
incorporating PCMs. Figure 1illustrates the structural framework of this review article.
Energies 2024, 17, x FOR PEER REVIEW 3 of 38
This research exclusively concentrates on the advancements in LHTS and explores poten-
tial enhancements that can be implemented in this type of storage.
This paper presents a comprehensive review and bibliometric analysis of HTEs ap-
plicable to HWGS using PCMs or other HTFs. Previous literature reviews have demon-
strated significant progress in various HTE methods across different applications, includ-
ing those relevant to this study. However, this new review offers a more focused approach,
highlighting the most commonly used techniques and those with potential for future re-
search in this field. As such, our analysis categorizes advancements into three primary
groups, active, passive, and hybrid methods employing PCMs, while also exploring the
use of nanofluids in solar collectors as an innovative heat storage solution. The main ob-
jective is to chart a course for HTEs that have seen widespread use or potential for future
application in HWGS incorporating PCMs. Figure 1 illustrates the structural framework
of this review article.
Figure 1. The structural framework of this review.
2. Methodology
This article employs bibliometric analysis, using the Scopus scientific database as its
primary methodology. The search was conducted until December 2023 to identify leading
countries and influential institutions that have significantly contributed to this topic. Ini-
tially, the focus was on advancements in heat transfer using PCMs for energy storage.
Consequently, the initial search was conducted using the keyword “heat transfer enhance-
ment” without any year or document type restrictions, resulting in 33,489 documents. To
refine the search, two specific keywords, “Domestic hot water” and “Phase Change Mate-
rial*” were added to narrow down the search to more relevant articles. The asterisk (*)
within the word facilitated our incorporation of the terms “Phase Change Material” and
“Phase Change Materials”. This refined approach ultimately led to the identification of
262 pertinent articles. Additionally, an exclusion criterion was implemented, specifically
targeting documents detailing methods of heat transfer enhancement (HTE) applicable to
domestic or residential hot water generation. Figure 2 visually represents the proposed
methodology, which will be employed in the subsequent sections.
Figure 1. The structural framework of this review.
2. Methodology
This article employs bibliometric analysis, using the Scopus scientific database as its
primary methodology. The search was conducted until December 2023 to identify lead-
ing countries and influential institutions that have significantly contributed to this topic.
Initially, the focus was on advancements in heat transfer using PCMs for energy storage.
Consequently, the initial search was conducted using the keyword “heat transfer enhance-
ment” without any year or document type restrictions, resulting in 33,489 documents.
To refine the search, two specific keywords, “Domestic hot water” and “Phase Change
Material*” were added to narrow down the search to more relevant articles. The asterisk (*)
within the word facilitated our incorporation of the terms “Phase Change Material” and
“Phase Change Materials”. This refined approach ultimately led to the identification of
262 pertinent articles. Additionally, an exclusion criterion was implemented, specifically
targeting documents detailing methods of heat transfer enhancement (HTE) applicable to
domestic or residential hot water generation. Figure 2visually represents the proposed
methodology, which will be employed in the subsequent sections.
Energies 2024,17, 2350 4 of 35
Energies 2024, 17, x FOR PEER REVIEW 4 of 38
Figure 2. Methodology used to search for information in Scopus.
3. Bibliometric Analysis
Following the methodology outlined in Figure 2, the search resulted in 130 final doc-
uments, forming the basis for the bibliometric analysis. In the initial analysis phase, re-
search trends were analyzed over the years to create a comprehensive overview.
3.1. Keyword Analysis
The co-occurrence of keywords in the documents was explored using VOSviewer
software, version 1.6.18. Figure 3 illustrates the frequency of keyword appearances, drawn
from a pool of 466 keywords. Only those mentioned at least five times were included in
the mapping, culminating in 24 distinct keywords. Notably, terms such as Phase Change
Materials, heat storage, heat transfer, thermal conductivity, and heat transfer en-
hancement aracted aention are illustrated by larger circles in Figure 3, indicating their
frequent recurrence in the studied documents.
Figure 3. Keyword co-occurrence network in heat transfer enhancement literature for latent heat
thermal storage.
Figure 2. Methodology used to search for information in Scopus.
3. Bibliometric Analysis
Following the methodology outlined in Figure 2, the search resulted in 130 final
documents, forming the basis for the bibliometric analysis. In the initial analysis phase,
research trends were analyzed over the years to create a comprehensive overview.
3.1. Keyword Analysis
The co-occurrence of keywords in the documents was explored using VOSviewer
software, version 1.6.18. Figure 3illustrates the frequency of keyword appearances, drawn
from a pool of 466 keywords. Only those mentioned at least five times were included
in the mapping, culminating in 24 distinct keywords. Notably, terms such as ‘Phase
Change Materials’, ‘heat storage’, ‘heat transfer’, ‘thermal conductivity’, and ‘heat transfer
enhancement’ attracted attention are illustrated by larger circles in Figure 3, indicating their
frequent recurrence in the studied documents.
Energies 2024, 17, x FOR PEER REVIEW 4 of 38
Figure 2. Methodology used to search for information in Scopus.
3. Bibliometric Analysis
Following the methodology outlined in Figure 2, the search resulted in 130 final doc-
uments, forming the basis for the bibliometric analysis. In the initial analysis phase, re-
search trends were analyzed over the years to create a comprehensive overview.
3.1. Keyword Analysis
The co-occurrence of keywords in the documents was explored using VOSviewer
software, version 1.6.18. Figure 3 illustrates the frequency of keyword appearances, drawn
from a pool of 466 keywords. Only those mentioned at least five times were included in
the mapping, culminating in 24 distinct keywords. Notably, terms such as Phase Change
Materials, heat storage, heat transfer, thermal conductivity, and heat transfer en-
hancement aracted aention are illustrated by larger circles in Figure 3, indicating their
frequent recurrence in the studied documents.
Figure 3. Keyword co-occurrence network in heat transfer enhancement literature for latent heat
thermal storage.
Figure 3. Keyword co-occurrence network in heat transfer enhancement literature for latent heat
thermal storage.
As illustrated in Figure 3, the interrelationships among keywords delineate a compre-
hensive network, suggesting that each keyword is intricately connected to others identified
Energies 2024,17, 2350 5 of 35
in the study. Furthermore, it is notable that terms such as ‘Phase Change Materials’ and
‘heat transfer enhancement’ exhibit frequent associations with concepts such as ‘fin’, ‘solar
energy’, ‘solar water heaters’, ‘latent heat thermal energy storage’, and ‘solar heating’.
3.2. Growth Trend of Documents on the Topic
Figure 4depicts the number of documents indexed in Scopus regarding the topic,
offering a glimpse into the progression of this topic over time. This figure reveals a
significant uptick in research and publications in the last three years (2021 to 2023). This
notable surge implies a growing interest in the topic, potentially driven by advancements
in PCMs for heat transfer applications, hot water generation, and building efficiency.
Energies 2024, 17, x FOR PEER REVIEW 5 of 38
As illustrated in Figure 3, the interrelationships among keywords delineate a com-
prehensive network, suggesting that each keyword is intricately connected to others iden-
tified in the study. Furthermore, it is notable that terms such as Phase Change Materials
and heat transfer enhancement exhibit frequent associations with concepts such as fin,
solar energy, solar water heaters, latent heat thermal energy storage, and solar heat-
ing.
3.2. Growth Trend of Documents on the Topic
Figure 4 depicts the number of documents indexed in Scopus regarding the topic,
offering a glimpse into the progression of this topic over time. This figure reveals a signif-
icant uptick in research and publications in the last three years (2021 to 2023). This notable
surge implies a growing interest in the topic, potentially driven by advancements in PCMs
for heat transfer applications, hot water generation, and building efficiency.
Figure 4. The trend of annual document publication in Scopus.
3.3. Number of Publications per Country
To investigate the global influence of the topic under investigation, a mapping was
conducted using the VOSviewer program (version 1.6.18), identifying contributions from
47 countries. Figure 5 showcases India in the lead with 38 documents, followed by China
with 34, and Iran with 17, underscoring their substantial research output. The nations
populations may contribute to their prominent positions in publication volume within this
domain [63]. Furthermore, VOSviewers analysis delves into the collaborative relation-
ships between countries, as evidenced by their joint research efforts. A notable partnership
between India and the United Kingdom is depicted by a sky-blue thicker line in Figure 5,
symbolizing their robust research collaboration. Additionally, the United Kingdom leads
in the number of citations with 2 953, followed by China with 2 476, and India with 1 614,
indicating the widespread global impact and recognition of their scientific contributions.
Figure 4. The trend of annual document publication in Scopus.
3.3. Number of Publications per Country
To investigate the global influence of the topic under investigation, a mapping was
conducted using the VOSviewer program (version 1.6.18), identifying contributions from
47 countries. Figure 5showcases India in the lead with 38 documents, followed by China
with 34, and Iran with 17, underscoring their substantial research output. The nations’
populations may contribute to their prominent positions in publication volume within this
domain [
63
]. Furthermore, VOSviewer’s analysis delves into the collaborative relationships
between countries, as evidenced by their joint research efforts. A notable partnership
between India and the United Kingdom is depicted by a sky-blue thicker line in Figure 5,
symbolizing their robust research collaboration. Additionally, the United Kingdom leads
in the number of citations with 2953, followed by China with 2476, and India with 1614,
indicating the widespread global impact and recognition of their scientific contributions.
3.4. Global Research Institutions Specializing in Heat Transfer Enhancement for LHTS
The analysis aimed to identify institutions distinguished for their prolific output or
trending productivity in publications. Consequently, a total of 334 entities were delineated,
both in higher education institutions and research organizations. Noteworthy entities
leading the list with a minimum of three publications include the Department of Refriger-
ation and Cryogenic Engineering at Xi’an Jiaotong University in China, the Department
of Mechanical Engineering at Babol Noshirvani University of Technology in Iran, and the
Center for Advanced Studies in Energy (USP-CAS-E) at the National University of Sciences
and Technology (NUST) in the U.S.–Pakistan collaboration. This investigation underscores
the pivotal role of academic institutions in driving research within this domain.
Energies 2024,17, 2350 6 of 35
Energies 2024, 17, x FOR PEER REVIEW 6 of 38
Figure 5. Global co-authorship network map in heat transfer enhancement for latent heat thermal
storage research.
3.4. Global Research Institutions Specializing in Heat Transfer Enhancement for LHTS
The analysis aimed to identify institutions distinguished for their prolific output or
trending productivity in publications. Consequently, a total of 334 entities were deline-
ated, both in higher education institutions and research organizations. Noteworthy enti-
ties leading the list with a minimum of three publications include the Department of Re-
frigeration and Cryogenic Engineering at Xian Jiaotong University in China, the Depart-
ment of Mechanical Engineering at Babol Noshirvani University of Technology in Iran,
and the Center for Advanced Studies in Energy (USP-CAS-E) at the National University
of Sciences and Technology (NUST) in the U.S.–Pakistan collaboration. This investigation
underscores the pivotal role of academic institutions in driving research within this do-
main.
3.5. Journals with More Documents
Table 1 shows the scientific journal articles that the authors used to disseminate their
research findings. Initially, 64 journals were identified through the analysis, but the table
has been refined to feature only those with at least two publications. Notably, the Journal
of Energy Storage emerges as the leading publication venue for articles on the topic, based
on author contributions. Furthermore, the analysis indicates a prevalent focus on engi-
neering and energy across most journals. Additional thematic areas encompass environ-
mental science, materials science, and social sciences, especially in research that intersects
sustainability with implementing HTEs in systems.
Table 1. Impactful journals on heat transfer enhancement for latent heat thermal storage research.
Journals Total Quantity
Journal of energy storage 22
Applied thermal engineering 11
Renewable and sustainable energy reviews 9
Renewable energy 6
Energy conversion and management 5
Energies 3
Figure 5. Global co-authorship network map in heat transfer enhancement for latent heat thermal
storage research.
3.5. Journals with More Documents
Table 1shows the scientific journal articles that the authors used to disseminate
their research findings. Initially, 64 journals were identified through the analysis, but the
table has been refined to feature only those with at least two publications. Notably, the
‘Journal of Energy Storage’ emerges as the leading publication venue for articles on the
topic, based on author contributions. Furthermore, the analysis indicates a prevalent focus
on engineering and energy across most journals. Additional thematic areas encompass
environmental science, materials science, and social sciences, especially in research that
intersects sustainability with implementing HTEs in systems.
Table 1. Impactful journals on heat transfer enhancement for latent heat thermal storage research.
Journals Total Quantity
Journal of energy storage 22
Applied thermal engineering 11
Renewable and sustainable energy reviews 9
Renewable energy 6
Energy conversion and management 5
Energies 3
Applied energy 3
International journal of heat and mass transfer 3
Solar energy 3
International journal of energy research 3
International communications in heat and mass transfer
3
Energy 2
Environmental science and pollution research 2
Journal of cleaner production 2
Materials today: proceedings 2
Case studies in thermal engineering 2
Progress in energy and combustion science 2
After conducting the bibliometric analysis, it was possible to examine bibliometric
data from documents identified as relevant according to the applied methodology. The
Energies 2024,17, 2350 7 of 35
techniques from various methods for enhancing heat transfer, as used in the field of potable
hot water generation, are analyzed based on the works of other authors, as illustrated
in Figure 1.
4. Heat Transfer Enhancements (HTEs) in Hot Water Generation Systems (HWGS)
The literature describes various methods to enhance heat transfer in HWGS. These
enhancements may involve modifications to the properties of the PCM [
64
] and alterations
to the generation system itself [
65
]. Figure 6illustrates various techniques for enhancing
heat transfer in LHTS systems based on the conducted study. Other authors classify these
techniques based on enhancements in thermal conductivity (such as carbon materials,
nanoparticles, metal foams, and graphite foams), enhancements in heat transfer efficiency
through convection (related to geometry), and optimization of the structure of phase change
devices (including fins, heat pipes, geometric configuration, and materials) [
20
,
28
,
66
,
67
]. In
addition to the methods and classifications detailed above, various other techniques exist,
including bubble agitation, metal rings, multitubes, carbon brushes, metal matrix, graphite
flakes, module beam, polypropylene flat panel, and compact flat panel. These methods
enhance heat transfer and find application across diverse contexts [68].
Energies 2024, 17, x FOR PEER REVIEW 7 of 38
Applied energy 3
International journal of heat and mass transfer 3
Solar energy 3
International journal of energy research 3
International communications in heat and mass transfer 3
Energy 2
Environmental science and pollution research 2
Journal of cleaner production 2
Materials today: proceedings 2
Case studies in thermal engineering 2
Progress in energy and combustion science 2
After conducting the bibliometric analysis, it was possible to examine bibliometric
data from documents identified as relevant according to the applied methodology. The
techniques from various methods for enhancing heat transfer, as used in the field of pota-
ble hot water generation, are analyzed based on the works of other authors, as illustrated
in Figure 1.
4. Heat Transfer Enhancements (HTEs) in Hot Water Generation Systems (HWGS)
The literature describes various methods to enhance heat transfer in HWGS. These
enhancements may involve modifications to the properties of the PCM [64] and alterations
to the generation system itself [65]. Figure 6 illustrates various techniques for enhancing
heat transfer in LHTS systems based on the conducted study. Other authors classify these
techniques based on enhancements in thermal conductivity (such as carbon materials, na-
noparticles, metal foams, and graphite foams), enhancements in heat transfer efficiency
through convection (related to geometry), and optimization of the structure of phase
change devices (including fins, heat pipes, geometric configuration, and materials)
[20,28,66,67]. In addition to the methods and classifications detailed above, various other
techniques exist, including bubble agitation, metal rings, multitubes, carbon brushes,
metal matrix, graphite flakes, module beam, polypropylene flat panel, and compact flat
panel. These methods enhance heat transfer and find application across diverse contexts
[68].
Figure 6. Heat transfer enhancement methods employed in this review.
Furthermore, an unconventional technique involving microorganisms has been iden-
tified [69]. However, this approach is considered somewhat inappropriate due to its asso-
ciation with water intended for human consumption, posing potential health risks. Nev-
ertheless, integrating it with other techniques to develop a safe heat storage system with-
out contaminating the water remains a subject for further exploration.
Figure 6. Heat transfer enhancement methods employed in this review.
Furthermore, an unconventional technique involving microorganisms has been iden-
tified [
69
]. However, this approach is considered somewhat inappropriate due to its
association with water intended for human consumption, posing potential health risks.
Nevertheless, integrating it with other techniques to develop a safe heat storage system
without contaminating the water remains a subject for further exploration.
In order to implement these enhancements in HWGS employing PCM, a wide range
of PCM options must be considered, as this selection significantly influences the effec-
tiveness of the heat storage system. Therefore, the primary properties to be evaluated
during this selection process include the temperature range, density, thermal conductiv-
ity, specific heat capacity, cost, and latent heat of fusion. Various approaches have been
used to customize the selection of materials according to specific requirements. These
approaches encompass multi-criteria decision-making methods (MCDM), such as the Ana-
lytic Hierarchy Process (AHP), TOPSIS (Technique for Order Performance by Similarity to
Ideal Solution), COPRAS (Complex Proportional Assessment), VIKOR (Vise Kriterijumska
Optimizacija Kompromisno Resenje), and others, serving as methodologies for material
selection [
3
,
5
,
70
]. When choosing a PCM, volume variation is another crucial criterion, as
it can significantly impact system efficiency. The PCM needs to exhibit minimal volume
changes [
35
,
68
,
71
,
72
]. While organic PCMs are often suggested for their potential to min-
imize volume changes [
12
,
20
,
67
,
73
], thorough verification is necessary to ensure future
operational integrity. In examining the volume variation of PCMs across different HTE
techniques, only a limited number of studies were discovered that illustrate PCM volume
changes as per the employed methodology. These studies indicate the following:
Energies 2024,17, 2350 8 of 35
•
PCM volume fluctuations during a phase change can potentially harm composite
PCMs (Graphite + PCM), yet they do not impair the heat transfer surface of the system
during solidification/melting cycles [74].
•
To mitigate pressure drops resulting from PCM volume changes, leaving a void space
within the tubes to accommodate PCM volume fluctuations is essential. Typically, only
90% of the evacuated tube solar collector’s tube is filled for this purpose [75].
•
When employing porous media, ensuring sufficient impregnation of PCM within
the foam facilitates the filling of empty pores during PCM volume alterations. This
safeguards the TES capacity from being compromised [12,66,76].
•
PCM encapsulation can mitigate volume changes resulting from phase transitions.
Macroencapsulation, in particular, is employed to increase the heat transfer area, thus
offsetting PCM volume changes [44].
•
Holes in PCM capsules can act as buffers for PCM volume expansion, typically used
in spherical encapsulation designs [20,77].
•
Due to PCM volume changes, high stresses occur in the annular fins after a certain
number of cycles. However, further research is needed on fluid–structure interaction
in TES systems with annular fins [71].
The subsequent subsections explore the methods that have been used or have the
potential to be employed in hot water generation, whether within storage tanks, shell-and-
tube TES units, solar collectors, or other relevant systems. These methods were selected
based on the articles reviewed in the bibliometric analysis.
4.1. Passive Methods
Passive methods are extensively embraced due to their reliance on surface modifica-
tions rather than external sources, resulting in simpler experimental development. These
methods are cost-effective compared to active approaches and provide versatility for many
applications [
69
]. Below, various techniques identified in the analysis of the selected articles
are outlined.
4.1.1. Fins
Fins represent a common method for enhancing the thermal conductivity heat transfer
coefficient and achieving a faster solidification process in heat exchangers [
78
,
79
]. Their
popularity stems from their simplicity, ease of manufacture, and cost-effectiveness [
80
].
Fins are typically extended on the PCM rather than the HTF side to enhance efficiency [
42
].
Fins facilitate heat transfer within these systems, and increasing their number and size can
significantly enhance system performance [
43
,
81
,
82
]. This assertion is supported by studies
such as Hosseine et al. [
83
], which propose that fin length is a critical parameter capable of
augmenting absorbed energy and reducing melting temperatures. Additionally, Kalbasi
and Salimbur [
84
] observe that a greater number of fins can lead to a more uniform temper-
ature distribution, optimizing the time required to reach peak temperature. Khan et al. [
85
]
corroborate these findings. Conversely, Al-Abidi et al. [
49
] suggest that fin thickness, length,
number, and the geometry of PCM units in Triplex Tube Heat Exchangers (TTHX), as well
as TTHX material and Stefan number, are pivotal parameters for hastening PCM fusion.
Tavakoli et al. [
86
] and Mao et al. [
87
] indicate that various geometric parameters can
influence the PCM melting time, along with the TES model in which the fins are situated.
However, Dinker et al. [
10
] note that reducing the fusion time may inversely impact the
overall system efficiency. Therefore, it is imperative to consider various parameters such as
inlet temperature, shape, and HTF flow rate during the charging period to mitigate PCM
melting time [88,89].
Fins can be manufactured in various shapes, including flat rectangular fins, rod-shaped
fins, and other irregular configurations, as illustrated in Figure 7. Research conducted
by Zhang et al. [
71
] indicates that longitudinal and annular fins have acquired the most
attention in the past decade. However, helical and topologically optimized fins (depicted in
Figure 7d) demonstrate exceptional potential due to their superior performance compared
Energies 2024,17, 2350 9 of 35
to traditional fins. This observation suggests that fins can be further improved using
various active and passive techniques for HTE.
Hosseini and Rahimi [
90
] highlight in their research that the position and size of
rectangular fins can significantly influence heat transfer distribution within energy storage
systems. So, to have a shorter melting time of the PCM, one must consider these parameters
in rectangular fins and possibly in other configurations. Amagour et al. [
91
] present a
three-dimensional numerical study of a fin-tube heat exchanger to assess HTE performance.
The findings indicate that increasing the HTF (water) flow rate reduces both charging and
discharging times. Conversely, elevating the HTF temperature accelerates the melting
process by up to 30% when there is a 10
◦
C temperature difference between the HTF and
the PCM; however, this also prolongs the solidification process.
Moreover, augmenting the number of fins decreases the heat transfer time and en-
hances the energy storage capacity. Nonetheless, the study suggests an upper limit to
the number of fins for effective enhancement. Additionally, the authors recommend po-
sitioning the fins in the middle of the heat exchanger, increasing fin thickness, and using
copper material, as these measures reduce the total melting time. In another study, Am-
agour et al. [
92
] indicate that a minimum of 8 h of hot water is required for residential
construction. Conversely, Chow and Lyu [
27
] propose a minimum requirement of 18 h
(from 7:00 am to 12:00 am) for residential applications.
Energies 2024, 17, x FOR PEER REVIEW 9 of 38
by studies such as Hosseine et al. [83], which propose that fin length is a critical parameter
capable of augmenting absorbed energy and reducing melting temperatures. Addition-
ally, Kalbasi and Salimbur [84] observe that a greater number of fins can lead to a more
uniform temperature distribution, optimizing the time required to reach peak tempera-
ture. Khan et al. [85] corroborate these findings. Conversely, Al-Abidi et al. [49] suggest
that fin thickness, length, number, and the geometry of PCM units in Triplex Tube Heat
Exchangers (TTHX), as well as TTHX material and Stefan number, are pivotal parameters
for hastening PCM fusion. Tavakoli et al. [86] and Mao et al. [87] indicate that various
geometric parameters can influence the PCM melting time, along with the TES model in
which the fins are situated. However, Dinker et al. [10] note that reducing the fusion time
may inversely impact the overall system efficiency. Therefore, it is imperative to consider
various parameters such as inlet temperature, shape, and HTF flow rate during the charg-
ing period to mitigate PCM melting time [88,89].
Fins can be manufactured in various shapes, including flat rectangular fins, rod-
shaped fins, and other irregular configurations, as illustrated in Figure 7. Research con-
ducted by Zhang et al. [71] indicates that longitudinal and annular fins have acquired the
most aention in the past decade. However, helical and topologically optimized fins (de-
picted in Figure 7d) demonstrate exceptional potential due to their superior performance
compared to traditional fins. This observation suggests that fins can be further improved
using various active and passive techniques for HTE.
Hosseini and Rahimi [90] highlight in their research that the position and size of rec-
tangular fins can significantly influence heat transfer distribution within energy storage
systems. So, to have a shorter melting time of the PCM, one must consider these parame-
ters in rectangular fins and possibly in other configurations. Amagour et al. [91] present a
three-dimensional numerical study of a fin-tube heat exchanger to assess HTE perfor-
mance. The findings indicate that increasing the HTF (water) flow rate reduces both charg-
ing and discharging times. Conversely, elevating the HTF temperature accelerates the
melting process by up to 30% when there is a 10 °C temperature difference between the
HTF and the PCM; however, this also prolongs the solidification process.
Moreover, augmenting the number of fins decreases the heat transfer time and en-
hances the energy storage capacity. Nonetheless, the study suggests an upper limit to the
number of fins for effective enhancement. Additionally, the authors recommend position-
ing the fins in the middle of the heat exchanger, increasing fin thickness, and using copper
material, as these measures reduce the total melting time. In another study, Amagour et
al. [92] indicate that a minimum of 8 h of hot water is required for residential construction.
Conversely, Chow and Lyu [27] propose a minimum requirement of 18 h (from 7:00 am
to 12:00 am) for residential applications.
(a) (b) (c) (d)
Energies 2024, 17, x FOR PEER REVIEW 10 of 38
(e)
Figure 7. Different shapes of fins: (a) branch-shaped fins [78] (CC by 4.0); (b) annular fins [43] (CC
by 4.0); (c) rectangular fins [93] (Copyright © 2013 Elsevier Ltd.); (d) twisted fins [94] (Copyright ©
2013 Elsevier Ltd.); (e) different fins of various researchers [95] (CC by 4.0).
Moreover, using copper strips shows promising potential for conduction HTE,
thereby reducing melting time by 16% [96]. Authors conducting numerical simulations
employ various methods to analyze fins in heat storage systems, including the Finite Vol-
ume and Enthalpy-Porosity methods [94]. Table 2 summarizes selected research studies
employing fins as an HTE technique.
Table 2. Most relevant research on fins in latent heat thermal storage.
Author PCM/HTF
Heat Exchanger
(HE)
Type
Study 3 Focus Study Results
Rahimi et
al. [97] RT35/H2O Rectangular tubu-
lar heat exchanger E Melting and solidifi-
cation process
• Solidification time is more affected than melting time.
• Increasing the flow rate can decrease both times.
• A better benefit is generated by using an inlet temperature of 50 to
60 °C.
Patel and
Rathod [98] RT50/H2O Triplex tube heat
exchanger (TTHX) N Melting and solidifi-
cation process
• Numerical study proves that the melting process can
b
e enhanced,
since conduction is dominant.
• Using internal and external fins (Figure 7c) can further help to re-
duce the melting time.
Shank et
al.[43] RT55/H2O
Latent Heat Ther-
mal Energy Stor-
age (LHTES) sys-
tem
E
Fins behavior in a
LHTS using two
configurations (10
annular fins and 20
annular fins).
• Shorter charging time and higher stored energy occur when the
charging temperature is high. If the flow rate increases, the charg-
ing and discharging period decreases (10 annular fins).
• Shorter charging and discharging time compared to the anterior
configuration due to the larger heat transfer area (20 annular fins).
Yang et al.
[99] PCM 1,2 Horizontal shell-
and-tube TES unit N Melting process
• PCM melting time can be significantly reduced from 6 to 52 fins in
a specific volume (Figure 8).
Kirincic et
al. [100] RT25/H2O Shell-and-tube N/E Melting and solidifi-
cation process
• The fins significantly enhance radial heat transfer, reducing melt-
ing time by 52% and solidification time by 43%.
• Faster storage rate.
Irbai et al.
[101]
Paraffin
wax/H2O -- N Melting process
• The novel geometry enhanced the melting process of a TES sys-
tem. PCM can melt in 900 s, three times faster than a conventional
longitudinal fin system.
Youssef et
al. [25]
A-16/A
mixture
of glycol
(25%)—wa-
ter
Indirect solar-as-
sisted heat pump
test system
N/E
Enhancing a solar
thermal system per-
formance
• The spiral-wired tubes can enhance thermal conductivity and al-
low free movement of the PCM during the melting process.
• In the numerical study, the charging times are faster than the dis-
charging times because of the contributions of convection and the
buoyancy effect generated on the PCM side.
• HTF charging temperature and flow rate can affect the charging
and discharging processes.
Rana et al.
[102] Gallium 2
HE with multiple
elliptical and circu-
lar tubes
N Thermal perfor-
mance of a HE
• Enhanced thermal performance.
• Melting time is reduced with the use of fins. The more fins, the
better the melting time.
• Cylindrical tubes can have better heat transfer than elliptical tubes.
Figure 7. Different shapes of fins: (a) branch-shaped fins [
78
] (CC by 4.0); (b) annular fins [
43
]
(
CC by 4.0
); (c) rectangular fins [
93
] (Copyright © 2013 Elsevier Ltd.); (d) twisted fins [
94
] (Copyright
© 2013 Elsevier Ltd.); (e) different fins of various researchers [95] (CC by 4.0).
Moreover, using copper strips shows promising potential for conduction HTE, thereby
reducing melting time by 16% [
96
]. Authors conducting numerical simulations employ
various methods to analyze fins in heat storage systems, including the Finite Volume and
Enthalpy-Porosity methods [
94
]. Table 2summarizes selected research studies employing
fins as an HTE technique.
Energies 2024,17, 2350 10 of 35
Table 2. Most relevant research on fins in latent heat thermal storage.
Author PCM/HTF Heat Exchanger (HE) Type Study 3Focus Study Results
Rahimi et al. [97] RT35/H2ORectangular tubular heat
exchanger EMelting and solidification
process
•Solidification time is more affected than melting time.
•Increasing the flow rate can decrease both times.
•
A better benefit is generated by using an inlet temperature of 50 to 60
◦
C.
Patel and Rathod [
98
]
RT50/H2OTriplextube heat exchanger
(TTHX) NMelting and solidification
process
•
Numerical study proves that the melting process can be enhanced, since
conduction is dominant.
•
Using internal and external fins (Figure 7c) can further help to reduce the
melting time.
Shank et al. [43] RT55/H2OLatent Heat Thermal Energy
Storage (LHTES) system E
Fins behavior in a LHTS
using two configurations
(10 annular fins and
20 annular fins).
•
Shorter charging time and higher stored energy occur when the charging
temperature is high. If the flow rate increases, the charging and
discharging period decreases (10 annular fins).
•Shorter charging and discharging time compared to the anterior
configuration due to the larger heat transfer area (20 annular fins).
Yang et al. [99]PCM 1,2 Horizontal shell-and-tube
TES unit N Melting process
•PCM melting time can be significantly reduced from 6 to 52 fins in a
specific volume (Figure 8).
Kirincic et al. [100] RT25/H2O Shell-and-tube N/E Melting and solidification
process
•
The fins significantly enhance radial heat transfer, reducing melting time
by 52% and solidification time by 43%.
•Faster storage rate.
Irbai’ et al. [101] Paraffin wax/H2O -- N Melting process
•
The novel geometry enhanced the melting process of a TES system. PCM
can melt in 900 s, three times faster than a conventional longitudinal
fin system.
Youssef et al. [25]A-16/A mixture
f glycol (25%)—water
Indirect solar-assisted heat
pump test system N/E Enhancing a solar thermal
system performance
•
The spiral-wired tubes can enhance thermal conductivity and allow free
movement of the PCM during the melting process.
•
In the numerical study,the charging times are faster than the discharging
times because of the contributions of convection and the buoyancy effect
generated on the PCM side.
•HTF charging temperature and flow rate can affect the charging and
discharging processes.
Rana et al. [102]Gallium 2
HE with multiple elliptical and
circular tubes NThermal performance
of a HE
•Enhanced thermal performance.
•
Melting time is reduced with the use of fins. The more fins, the better the
melting time.
•Cylindrical tubes can have better heat transfer than elliptical tubes.
Liu and Groulx [103] Lauric acid/H2O
Horizontal cylindrical latent
heat energy storage
system (LHESS)
EMelting and solidification
process
•HTF inlet temperature can affect the complete PCM melting time, while
HTF flow rates are the least affected.
•Angled fins show a lower melting time than straight fins when the HTF
inlet temperature is 50 ◦C.
•If the temperature rises, neither fin has a significant
enhancement difference.
1
PCM is not specified/disclosed.
2
HTF is no specified/disclosed.
3
Type of study: N = numerical; and
E = experimental.
Energies 2024, 17, x FOR PEER REVIEW 11 of 38
Liu and
Groulx
[103]
Lauric
acid/H
2
O
Horizontal cylin-
drical latent heat
energy storage sys-
tem (LHESS)
E Melting and solidifi-
cation process
• HTF inlet temperature can affect the complete PCM melting time,
while HTF flow rates are the least affected.
• Angled fins show a lower melting time than straight fins when the
HTF inlet temperature is 50 °C.
• If the temperature rises, neither fin has a significant enhancement
difference.
1
PCM is not specified/disclosed.
2
HTF is no specified/disclosed.
3
Type of study: N = numerical; and
E = experimental.
The literature review underscores the widespread utilization of rectangular fins for
HTE across various applications. Their simplicity in design and low manufacturing com-
plexity renders them highly favored. The findings of these studies highlight a significant
potential for improving heat transfer in LHTESS. Notably, the methodology employed
revealed a paucity of studies addressing the real-world application of hot water, with most
being either numerical or laboratory-scale investigations. Consequently, a research gap
exists regarding both simple and complex-shaped fins ability to enhance heat transfer in
these systems. In addition to numerical analyses, experimental studies are imperative to
validate the efficacy of this technique in HWGS. The outcomes of these studies underscore
the pivotal role of the number of fins in LHTESS. While some studies suggest a progressive
improvement in heat transfer efficiency with an increased number of fins, others indicate
that this relationship has a finite range beyond which further enhancement ceases. There-
fore, it is crucial to corroborate this information, as only numerical data are available on
this aspect (see Figure 8). Moreover, investigating the use of various fin shapes in LHTESS
is essential, as it can explain which of the shapes studied in the literature yield superior
results.
Figure 8. Total melting time for various fin numbers [99] (Copyright © 2021 Elsevier B.V.).
4.1.2. Turbulators
Turbulators represent passive methods characterized by spiral inserts elevating fluid
velocity within tubes. Turbulators use discs, twisted tapes, wire coils, and others. Turbu-
lators look like fins but differ in their twisted geometry [104]. Typically composed of car-
bon steel, stainless steel, or copper, turbulators promote HTE and increase flow turbulence
[105,106]. Research indicates that this method of heat enhancement surpasses the efficacy
of using simple-shaped tubes in SWHS [107]. The subsequent section outlines selected
studies from the literature pertaining to this topic.
Twisted tapes and turbulators can potentially increase heat transfer and performance,
contingent upon the type of solar collector employed. Nevertheless, this passive technique
exhibits somewhat restricted applicability in hot water generation or solar collectors
[108,109]. Jaisankar et al. [110] undertook a study to investigate the impact of heat transfer
from a collector enhanced with a helically twisted tape. Their findings revealed that using
Figure 8. Total melting time for various fin numbers [99] (Copyright © 2021 Elsevier B.V.).
The literature review underscores the widespread utilization of rectangular fins for
HTE across various applications. Their simplicity in design and low manufacturing com-
plexity renders them highly favored. The findings of these studies highlight a significant
potential for improving heat transfer in LHTESS. Notably, the methodology employed
revealed a paucity of studies addressing the real-world application of hot water, with most
being either numerical or laboratory-scale investigations. Consequently, a research gap
exists regarding both simple and complex-shaped fins’ ability to enhance heat transfer
in these systems. In addition to numerical analyses, experimental studies are imperative
to validate the efficacy of this technique in HWGS. The outcomes of these studies un-
derscore the pivotal role of the number of fins in LHTESS. While some studies suggest
a progressive improvement in heat transfer efficiency with an increased number of fins,
Energies 2024,17, 2350 11 of 35
others indicate that this relationship has a finite range beyond which further enhancement
ceases. Therefore, it is crucial to corroborate this information, as only numerical data are
available on this aspect (see Figure 8). Moreover, investigating the use of various fin shapes
in LHTESS is essential, as it can explain which of the shapes studied in the literature yield
superior results.
4.1.2. Turbulators
Turbulators represent passive methods characterized by spiral inserts elevating fluid
velocity within tubes. Turbulators use discs, twisted tapes, wire coils, and others. Tur-
bulators look like fins but differ in their twisted geometry [
104
]. Typically composed of
carbon steel, stainless steel, or copper, turbulators promote HTE and increase flow turbu-
lence [
105
,
106
]. Research indicates that this method of heat enhancement surpasses the
efficacy of using simple-shaped tubes in SWHS [
107
]. The subsequent section outlines
selected studies from the literature pertaining to this topic.
Twisted tapes and turbulators can potentially increase heat transfer and perfor-
mance, contingent upon the type of solar collector employed. Nevertheless, this pas-
sive technique exhibits somewhat restricted applicability in hot water generation or solar
collectors [108,109].
Jaisankar et al. [
110
] undertook a study to investigate the impact of heat
transfer from a collector enhanced with a helically twisted tape. Their findings revealed
that using a helically twisted tape can elevate the heat transfer rate, pressure drop, and
thermal efficiency by enhancing the tape’s solar radiation and twist ratio.
Li et al. [
94
] conducted a similar study, only that they are called twisted fins or helical
fins since these are located outside the tube through which the HTF (water) passes. In
their numerical investigation, they examined the application of shell-and-tube-based heat
storage with twisted fins to enhance the performance of this storage type. Their study
encompassed various configurations of twisted fins, ranging from 0 to 4 fins positioned
around the base tube, and was conducted in two orientations: vertical and horizontal.
Their findings indicate that the configuration featuring three twisted fins enhances the
melting time of the PCM in the vertical orientation, while in the horizontal orientation, the
configuration with two twisted fins yielded the most favorable melting time. Consequently,
the authors concluded that increasing the number of twisted fins does not necessarily
correspond to a performance enhancement.
Not all researchers confirm the efficacy of turbulator-based enhancement methods.
For instance, Hobbi et al. [
111
] explored the influence of various passive devices (including
twisted strips, coil-spring wires, and conical ridges) on a flat plate solar collector. Their
findings suggest that these turbulence enhancement techniques fail to significantly increase
heat transfer, as evidenced by the absence of discernible differences in the heat flow to
the fluid.
The use of turbulators in LHTESS remains limited. Nevertheless, considering their
association with fins, it represents an area warranting further investigation and expansion.
The literature review reveals divergent viewpoints regarding the effectiveness of turbu-
lators, which may stem from variations in methodology, collector size, or experimental
setups adopted by researchers. The studies identified in this review primarily focused
on systems employing tubes or solar collectors, as turbulators are commonly deployed to
augment fluid velocity within the tubes. Notably, no explicit investigations were found
about using coils in storage tanks. This presents a research opportunity to enhance HTF
velocity within the coils, potentially improving the melting efficiency.
4.1.3. Porous Media (PM) or Foams
PCMs represent a promising avenue for enhancing energy efficiency and sustainability
within systems. Researchers have explored various methodologies to augment thermal con-
ductivity, among which the utilization of PM or metal foams stands out. These materials are
favored for their robust, highly conductive, and permeable structures. The literature reveals
a diversity of models, materials, pore densities, and porosities employed in fabricating
Energies 2024,17, 2350 12 of 35
foams or PM. However, the efficacy of this technique is compromised by the inherent natural
convection of the material [
12
,
44
]. Moreover, numerous numerical methods are available for
modeling this technique, with the Lattice Boltzmann method emerging as the most preva-
lent [
112
,
113
]. Alternatively, Habibishandiz et al. [
69
] demonstrate several models capable
of simulating velocity within the PM, including the Darcy model,
Darcy–Forchheimer (DF)
model, Darcy–Brinkman (DB) model, and Darcy–Brinkman–Forchheimer (DBF) model.
Majdi et al. [
114
] indicate that incorporating PM within a tank can significantly extend
the thermal storage duration compared to systems lacking such media. Furthermore, the
thermal conductivity of PCMs can be substantially augmented through metallic foams,
with copper foam exhibiting a 44-fold increase and aluminum foam exhibiting a remarkable
218-fold increase when configured with 89% and 71% porosities, respectively. Additionally,
employing the impregnation method proves beneficial in minimizing empty pores within
the PCM, thereby mitigating undesired thermal resistance [
76
]. It is important to acknowl-
edge that these enhancements may vary based on several factors inherent to the system;
nonetheless, experimental investigations have demonstrated HTEs of up to 400% [
115
,
116
].
Conversely, Zhang et al. [
117
] illustrate that the effectiveness of metallic foam in HTE is
contingent upon factors such as porosity, pore density, and thermal conductivity.
The utilization of metallic foams in various applications has acquired significant
interest. In a study by Xiao et al. [
118
], two types of metallic foams, copper and nickel, were
compared for their effectiveness in creating a composite PCM. Their findings revealed that
the copper metal foam exhibited a superior enhancement in thermal conductivity compared
to its nickel counterpart. Similarly, Aramesh and Shabani [
75
] conducted a comparative
analysis involving different setups: (a) no PCM, (b) pure PCM, (c) PCM with fins, and
(d) PCM
with metal foam in an evacuated tube solar collector. While the absence of PCMs
(setup a) resulted in a higher outlet temperature, it lacked the energy storage capability
observed in setups involving PCM (b, c, d). Notably, setup (d) incorporating PCM with
metal foam exhibited a reduced temperature drop, enhanced heat storage, improved heat
transfer performance within the tubes, and higher overall efficiency. Further investigations
exploring the application of this technique can be found in Table 3.
The remarkable thermal conductivity of metallic foams facilitates the solidification and
melting processes of PCMs. However, choosing an appropriate position when placing the
PCM is necessary, as this will allow for a more efficient heat transfer. This observation was
only made in LHTESS with tubes. Regarding the application of this technique, few current
studies validate the results in hot water generation, whether using solar collectors or storage
tanks. Nevertheless, the collective evidence from reviewed studies consistently highlights
the exceptional performance of copper metallic foams. Therefore, it is recommended to
prioritize investigations focusing on copper metallic foams as a foundational starting point
for future research endeavors in this domain.
Table 3. Research about porous media in the literature.
Author PCM/HTF Porous Media Type Study 3Focus Study Results
Zhu et al. [65]Paraffin wax 2Copper metal foam N/E Melting process
•
Increasing the proportion of metal foam decreased the melting time of the material.
•Heat storage rate increased.
•Enhanced thermal conductivity.
•
Weakening of natural convection heat transfer because the metal foam restrictsthe
natural convection of the PCM.
Zhu et al. [119]Paraffin wax 2Copper metal foam E Melting process
•Increased PCM melting time.
•Increasing the proportion of metal foam can increase heat transfer by conduction.
Alam et al. [120] n-eicosane/H2O Copper metal foam N Solidification process
•Decreased porosity in the PM can favor solidification by decreasing it, thanks to
the thermal conductivity of PM.
•Performance improvements are observed during the discharging phase when
using PM, particularly when the PCM is in direct contact with the HTF.
•Using the M-11 configuration has a solidification time reduction of up to 91.1%
compared to M-1 (Figure 9), but the cost can be high.
Wang et al. [121]Paraffin wax 2Copper metal foam
(Porosity 95%, pore
density 5PPI)
E Melting process
•Increasing the PM proportion decreases the discharging time and
temperature gradient.
•Heat storage rate and integrated heat transfer coefficient increased.
•Heat conduction plays an important role in this HTE method.
Energies 2024,17, 2350 13 of 35
Table 3. Cont.
Author PCM/HTF Porous Media Type Study 3Focus Study Results
Yang et al. [122] Paraffin/H2O Open-cell metal foam E Melting process
•Under the use of different inlet velocities, the efficiency of TES increased.
•Melting time was reduced by 64%, and there was better temperature distribution
due to foam conduction.
Baruah et al. [123]PCM 1,2 Capsules of metal foam N Melting process
•The metal foam can increase heat transfer and thus enhance the melting process.
•By reducing the capsule’s size and the metal foam’s porosity,a higher cover
thickness is achieved, and thus, better melting time results are achieved.
1
PCM is not specified/disclosed.
2
HTF is not specified/disclosed.
3
Type of study: N = numerical and
E = experimental.
Energies 2024, 17, x FOR PEER REVIEW 14 of 38
Figure 9. Different configurations about the use of porous media [120] (Copyright © 2013 Elsevier
Ltd.).
4.1.4. Encapsulation
Encapsulation involves enveloping a material with a protective coating, which is cru-
cial in LHTESS. Various types of coatings, including metallic, inorganic, and plastic, ne-
cessitate careful selection for optimal performance [21]. Encapsulation serves several key
purposes, including isolating the PCM from the external environment, preventing direct
contact with the HTF, mitigating external volume change reactions, enhancing system ef-
ficiency, and augmenting the heat transfer surface [85]. Different integration methods for
PCM encapsulation exist, such as macroencapsulation (approximately 1 mm), microen-
capsulation (0–1000 µm), nanoencapsulation (0–1000 nm), immersion, and direct incorpo-
ration [44,72,124]. While various PCMs can be encapsulated, paraffin wax and sodium ac-
etate trihydrate are commonly employed in this context. Among the available encapsula-
tion materials, plastic, aluminum, and stainless steel are frequently used for macroencap-
sulation [125]. In contrast, although more intricate in manufacturing, microencapsulation
offers superior heat transfer capabilities [126]. Encapsulation with metallic materials like
copper, aluminum, and steel presents an aractive option for enhancing thermal conduc-
tivity. However, it poses manufacturing challenges [85]. Figure 10 illustrates diverse ways
of PCM encapsulation.
Figure 10. Various configurations of PCM encapsulation [126] (Copyright © 2012 Elsevier Ltd.).
Different parameters must be considered when encapsulating a PCM, as they can
affect or enhance heat transfer. These parameters are the shell material, geometry, and
core-to-coating ratio (decides the encapsulated PCMs mechanical strength and thermal
stability). Additionally, factors such as the Stefan number, the temperature range of the
PCM, and the volumetric concentration of the microcapsule can exert a significant
Figure 9. Different configurations about the use of porous media [
120
] (Copyright © 2013 Elsevier Ltd.).
4.1.4. Encapsulation
Encapsulation involves enveloping a material with a protective coating, which is
crucial in LHTESS. Various types of coatings, including metallic, inorganic, and plastic,
necessitate careful selection for optimal performance [
21
]. Encapsulation serves several key
purposes, including isolating the PCM from the external environment, preventing direct
contact with the HTF, mitigating external volume change reactions, enhancing system
efficiency, and augmenting the heat transfer surface [
85
]. Different integration methods
for PCM encapsulation exist, such as macroencapsulation (approximately 1 mm), mi-
croencapsulation (0–1000
µ
m), nanoencapsulation (0–1000 nm), immersion, and direct
incorporation [
44
,
72
,
124
]. While various PCMs can be encapsulated, paraffin wax and
sodium acetate trihydrate are commonly employed in this context. Among the available
encapsulation materials, plastic, aluminum, and stainless steel are frequently used for
macroencapsulation [
125
]. In contrast, although more intricate in manufacturing, microen-
capsulation offers superior heat transfer capabilities [
126
]. Encapsulation with metallic
materials like copper, aluminum, and steel presents an attractive option for enhancing ther-
mal conductivity. However, it poses manufacturing challenges [
85
]. Figure 10 illustrates
diverse ways of PCM encapsulation.
Different parameters must be considered when encapsulating a PCM, as they can
affect or enhance heat transfer. These parameters are the shell material, geometry, and
core-to-coating ratio (decides the encapsulated PCM’s mechanical strength and thermal
stability). Additionally, factors such as the Stefan number, the temperature range of the
PCM, and the volumetric concentration of the microcapsule can exert a significant influence
on heat transfer [
126
]. One of the significant challenges associated with encapsulating
materials is the risk of leakage. Therefore, conducting leakage analysis on the PCM during
encapsulation is essential to ensure its reliability before deploying it in practical applica-
Energies 2024,17, 2350 14 of 35
tions. Leakage analysis involves subjecting the encapsulated PCM to thermal cycling and
thorough cleaning procedures to assess its integrity and performance [127].
Energies 2024, 17, x FOR PEER REVIEW 14 of 38
Figure 9. Different configurations about the use of porous media [120] (Copyright © 2013 Elsevier
Ltd.).
4.1.4. Encapsulation
Encapsulation involves enveloping a material with a protective coating, which is cru-
cial in LHTESS. Various types of coatings, including metallic, inorganic, and plastic, ne-
cessitate careful selection for optimal performance [21]. Encapsulation serves several key
purposes, including isolating the PCM from the external environment, preventing direct
contact with the HTF, mitigating external volume change reactions, enhancing system ef-
ficiency, and augmenting the heat transfer surface [85]. Different integration methods for
PCM encapsulation exist, such as macroencapsulation (approximately 1 mm), microen-
capsulation (0–1000 µm), nanoencapsulation (0–1000 nm), immersion, and direct incorpo-
ration [44,72,124]. While various PCMs can be encapsulated, paraffin wax and sodium ac-
etate trihydrate are commonly employed in this context. Among the available encapsula-
tion materials, plastic, aluminum, and stainless steel are frequently used for macroencap-
sulation [125]. In contrast, although more intricate in manufacturing, microencapsulation
offers superior heat transfer capabilities [126]. Encapsulation with metallic materials like
copper, aluminum, and steel presents an aractive option for enhancing thermal conduc-
tivity. However, it poses manufacturing challenges [85]. Figure 10 illustrates diverse ways
of PCM encapsulation.
Figure 10. Various configurations of PCM encapsulation [126] (Copyright © 2012 Elsevier Ltd.).
Different parameters must be considered when encapsulating a PCM, as they can
affect or enhance heat transfer. These parameters are the shell material, geometry, and
core-to-coating ratio (decides the encapsulated PCMs mechanical strength and thermal
stability). Additionally, factors such as the Stefan number, the temperature range of the
PCM, and the volumetric concentration of the microcapsule can exert a significant
Figure 10. Various configurations of PCM encapsulation [126] (Copyright © 2012 Elsevier Ltd.).
Microencapsulation presents an opportunity to improve the energy storage efficiency
and enhance various thermal properties in direct absorption solar collectors [
128
]. This is
because there is no change in the velocity of water and microencapsulated PCM product of
microencapsulation; a diameter of 5
µ
m is recommended to enhance the performance [
129
].
Nanoencapsulation of PCM offers benefits such as improved thermal conductivity, leak-
age prevention, reduced overcooling, and increased suspension capacity at the melting
temperature [124,130].
Certain investigations into cylindrical macroencapsulation have demonstrated its
potential to increase energy storage density and prolong the storage duration. However,
simply increasing the PCM amount does not necessarily improve the system’s thermal
performance, as a critical threshold exists for PCM quantity [
131
,
132
]. In a study by Sun
et al. [
133
], an experimental–numerical analysis was conducted to evaluate the impact of
integrating encapsulated PCMs into a water storage tank linked to four unglazed monocrys-
talline photovoltaic–thermal (PVT) modules. Their findings indicated a slight increase in
average and overall electrical efficiency; however, the authors caution that alterations may
influence these values in the flow rate.
Other studies have explored spherical encapsulation, such as the investigation by
Nallusamy et al. [
15
], who employed spherically encapsulated paraffin with high-density
polyethylene in a hybrid storage system combining sensible and latent heat. Their findings
indicated a faster discharge period, suggesting this hybrid system is well-suited for inter-
mittent hot water discharge systems. In a separate study, Shin et al. [
77
] compared elliptical
and spherical capsules with the elliptical capsule, composed of polyethylene, aimed at en-
hancing heat transfer. The results demonstrated that the elliptical geometry could increase
the Nusselt number by fivefold, reducing the charging and discharging times by 50% and
35%, respectively. Moreover, this experiment, conducted on a large scale, exhibited favorable
charge and discharge times, suggesting its potential as a thermal battery.
PCM encapsulation is common in storage tanks, particularly for prolonged hot wa-
ter generation. Macroencapsulation, owing to its affordability, has garnered significant
attention, especially in mixed heat storage systems like LHTS-SHTS. However, real-world
applications of encapsulation in solar collectors remain largely unexplored, predominantly
confined to laboratory-scale investigations, thus presenting a promising avenue for future
research. Additionally, exploring diverse macroencapsulation geometries can enhance heat
transfer efficiency by augmenting the surface area for heat transfer. Nonetheless, while
microencapsulation demonstrates promising outcomes, its high manufacturing cost poses
a significant limitation, rendering it less accessible for LHTESS applications.
Furthermore, a techno-economic analysis was conducted to investigate the casing cost
and encapsulation methods [
47
]. Findings revealed that PCM encapsulated with aluminum
alloy, titanium, and carbonate tubes offer a cost-effective solution for their deployment.
Moreover, the overall cost of encapsulation is contingent upon the casing material and
encapsulation technique employed, with due consideration to the minimal cost associated
with PCM itself.
Energies 2024,17, 2350 15 of 35
4.1.5. Geometry and Orientation Variation
The geometry and orientation of TES systems play a crucial role in determining their
performance. Therefore, it is essential to select a geometry that ensures uniform temperature
distribution within the TES system and to consider the container orientation, which can
influence heat transfer [
85
]. Various LHTS geometries are available, including circular,
cylindrical shell and tube, rectangular, and triplex tube configurations (which consist of
a cylinder with two tubes of different sizes inside, facilitating the exchange of HTF and
PCM) [
6
]. This method offers long-term viability compared to alternative techniques like
nanoparticles and fins. Notably, the container’s inclination angle can impact melting and
solidification rates [
134
]. Additionally, the TES system can be enhanced by modifying the
container geometry or the tubes through which the HTF flows.
Yan et al. [
135
] conducted a numerical study investigating the impact of altering the
shape of a cylindrical latent heat storage unit (CLHSU) on both the charging and discharging
times. Figure 11 illustrates the CLHSU before and after the geometry modification. The
study focused on varying the wavelength (Lw) and wavelength amplitude (aw) to assess
their effects on the charging and discharging times. Results indicated significant changes
in the heat transfer coefficient and the velocity of PCM during these processes. During
discharging, the heat transfer coefficient experienced a slight 2% decrease due to the
corrugated wall but remained higher than that of the CLHU-S model.
E ne r gies 2 0 2 4 , 1 7, x F O R P E E R R E VI E W 1 6 of 3 8
P C M) [ 6]. T his m et h o d o ff e r s l o n g-t er m vi a bilit y c o m p ar e d t o alt e r n ati v e t e c h ni q u es li ke
n a n o p arti cl es a n d fi ns. N ot a bl y, t h e c o nt ai n er s i ncli n ati o n a n gl e c a n i m p a ct m elti n g a n d
s oli difi c ati o n r at e s [ 1 3 4]. A d diti o n all y, t h e T E S s y st e m c a n b e e n h a n c e d b y m o dif yi n g t h e
c o nt ai n er g e o m et r y or t he t u be s t hr o u g h w hic h t he H T F fl o w s.
Ya n et al. [ 1 3 5] c o n d uct e d a n u m e ri c al st u d y i n vesti g ati n g t h e i m p a ct of alt eri n g t he
s h a p e of a c yli n dri c al l at e nt h e at st or a g e u nit ( C L H S U) o n b ot h t h e c h ar gi n g a n d di s c h a r g-
i n g ti m e s. Fi g ur e 1 1 ill ustr at es t h e C LH S U b ef or e a n d aft er t h e g e o m etr y m o di fi c ati o n.
T h e st u d y f oc us e d o n v a r yi n g t h e w a v el e n gt h ( L w) a n d w a v el e n gt h a m plit u d e ( a w) t o
as s e s s t h eir e ff e ct s o n t h e c h ar gi n g a n d di s c h ar gi n g ti m e s. R e s ult s i n dic at e d si g ni fi c a nt
c h a n g es i n t h e h e at t r a nsf e r c o e ffi ci e nt a n d t h e v el o cit y of P C M d uri n g t h es e pr oc e ss es.
D uri n g di s c h ar gi n g, t h e h e at tr a nsf er c o e ffi ci e nt e x p eri e n c e d a sli g ht 2 % d e c r e a s e d u e t o
t h e c orr u g at e d w all b ut r e m ai n e d hi g h e r t h a n t h at of t h e C L H U- S m o del.
(a ) (b )
Fi g ur e 1 1. G e o m etr y c h a n ge d b y Y a n et al. [ 1 3 5] ( C o p yri g ht © 2 0 2 3 Els e vi e r Lt d.): ( a ) c yli n dri c al
l at e nt h e at st or a ge u nit wit h o ut wa v e s ( C L H S U- S) a n d wit h o ut wa ve s ( C L H S U- W); (b ) c o m p ut a-
ti o nal d o m ai n of t h e C L H S U- W.
M or e o v er, it w a s n ot e d t h at t h e p ar a m et er s L w a n d a w pl a y e d a mi n or r ol e i n t h e
dis c h ar gi n g pr oc ess b u t h a d a m or e pr o n o u nc e d i m p a ct d uri n g c h ar gi n g. A d diti o n all y,
A g g ar w al et al. [ 1 7] hi g hli g ht e d i n t h eir r es e ar c h t h e si g nifi c a n c e of t h e tilt a n gl e of e v a c-
u at e d t u b e s ol a r c olle ct or s ( E T S C s) i n e n h a n ci n g e ff e cti v e n e s s a n d c ost e ffi ci e n c y ac r o s s
di ff e r e nt g e o gr a p hi c al r e gi o ns. T h u s, it i s i m p e r ati v e t o c o nsi d er t his f act or w h e n pl a n ni n g
t h e i nst all ati o n of a H W G S b a s e d o n t h e s p ecifi c l oc ati o n of t h e st u d y.
Alt h o u g h t h e n u m e ri c al i n vesti g ati o n c o n d u ct e d b y Q uiti a q u e z et al. [ 1 3 6] f o c u s es o n
e n h a n ci n g he at tr a nsf er wit hi n a s ol ar c oll e ct or/ e v a p or at or pri m aril y u s e d i n h e ati n g s ys-
t e ms, it r e ve al s a n ot a bl e i m pr o v e me nt i n h eat g e n e r ati o n w h e n m o dif yi n g t h e cr os s- s e c-
ti o n of t h e t u be s, as ill ustr at e d i n Fi g ur e 1 2. As a r e s ult, alt er n ati v e g e o m et ri es ar e bei n g
c o nsi d er e d f or H W G S. H o w e v er, a n e c o n o mic a n al ysis is i m p e r ati v e t o d et e r mi n e
w h et h e r t his e n h a n c e me nt is ec o n o mi c all y vi a bl e f or e n h a n ci n g s yst e m p erf or m a n c e. A d-
diti o n all y, e x p e ri me nt al vali d ati o n is e s s e nti a l t o a s c e rt ai n w h et h er alt e ri n g t u be or st or-
a g e t a n k ge o m et r y c a n e n h a n c e e ffi ci e nc y a n d r e d uc e t h e c h ar gi n g a n d dis c h ar gi n g ti m e s
of L H T E S S.
Figure 11. Geometry changed by Yan et al. [
135
] (Copyright © 2023 Elsevier Ltd.): (a) cylindrical
latent heat storage unit without waves (CLHSU-S) and without waves (CLHSU-W); (b) computational
domain of the CLHSU-W.
Moreover, it was noted that the parameters Lw and aw played a minor role in the
discharging process but had a more pronounced impact during charging. Additionally,
Aggarwal et al. [
17
] highlighted in their research the significance of the tilt angle of evac-
uated tube solar collectors (ETSCs) in enhancing effectiveness and cost efficiency across
different geographical regions. Thus, it is imperative to consider this factor when planning
the installation of a HWGS based on the specific location of the study.
Although the numerical investigation conducted by Quitiaquez et al. [
136
] focuses
on enhancing heat transfer within a solar collector/evaporator primarily used in heating
systems, it reveals a notable improvement in heat generation when modifying the cross-
section of the tubes, as illustrated in Figure 12. As a result, alternative geometries are being
considered for HWGS. However, an economic analysis is imperative to determine whether
this enhancement is economically viable for enhancing system performance. Additionally,
experimental validation is essential to ascertain whether altering tube or storage tank
geometry can enhance efficiency and reduce the charging and discharging times of LHTESS.
Energies 2024,17, 2350 16 of 35
Energies 2024, 17, x FOR PEER REVIEW 17 of 38
(a) (b) (c)
(d) (e)
Figure 12. Different geometries [136] (CC by 4.0). (a) Three-leaf clover; (b) hexagonal; (c) flower; (d)
internal circular section with a flower shape in the external profile; (e) four-leaf clover.
4.1.6. Composite Phase Change Materials (CPCMs)
CPCMs are favored for energy storage due to their exceptional thermal conductivity,
low cost, enhanced productivity, chemical stability, corrosion resistance, and thermal dif-
fusivity [81]. Certain CPCMs incorporate nanofillers like graphite, graphene oxide (GO),
and hexagonal boron nitride (HBN), which significantly augment the thermal properties
of the PCM, thereby benefiting solar energy storage systems [137]. Additionally, CPCMs
with additives or nanoparticles such as expanded graphite (EG) and carbon fiber (CF) ex-
hibit favorable thermochemical properties, high thermal conductivity, and remarkable
heat storage capacity [44].
Nanoparticles, characterized by their dimensions smaller than 100 nm, exhibit ther-
mal conductivity influenced by several factors such as concentration, temperature, particle
size, pH, shape, material composition, and potentially the manufacturing process [1]. The
literature highlights diverse methods for synthesizing nanoparticles from disposable ma-
terials, as delineated in Table 4. However, exploring the feasibility of producing nanopar-
ticles from waste materials remains relatively unexplored. Conversely, limited research
delves into the cost-effectiveness of incorporating nanoparticles in PCM preparation, par-
ticularly regarding implementation expenses for specific applications. While some studies
demonstrate the enhancement of PCM thermal conductivity by adding expanded graphite
or graphite nanoparticles, it is noteworthy that this augmentation affects thermal conduc-
tivity, melting time, and overall thermal performance positively [138–140].
Table 4. Nanoparticles consisting of industrial waste materials [141].
Author Waste Materials Nanoparticle
Hu et al. [142] Waste plastic bags Carbon nanoparticles
Hassan et al. [143] Eggshell powder Biobased calcium carbonate nanoparticles
Biswas et al. [144] Waste iron Magnetic iron oxide nanoparticles
Rajarao et al. [145] Silicon dioxide and electronic waste compact discs Silicon carbide nanoparticles
Rangari et al. [146] Egg, mussel, and quahog shells Biobased nanoparticles
DOliveira et al. [141] demonstrated the capacity of highly conductive nanoparticles
to augment the thermal conductivity of PCM with low melting temperatures (ranging
from 20 to 70 °C). The literature underscores the potential of carbon-based nanoparticles
to supplant conventional metallic nanoparticles due to their commendable stability and
ability to enhance PCM thermal conductivity [45,147,148]. In comparison, H.M Teamah
and M. Teamah [149] agree on carbon-based nanoparticles but indicate that metallic foams
are also strong candidates. In a study by Cabeza et al. [150], a CPCM comprising 10%
Figure 12. Different geometries [
136
] (CC by 4.0). (a) Three-leaf clover; (b) hexagonal; (c) flower;
(d) internal circular section with a flower shape in the external profile; (e) four-leaf clover.
4.1.6. Composite Phase Change Materials (CPCMs)
CPCMs are favored for energy storage due to their exceptional thermal conductivity,
low cost, enhanced productivity, chemical stability, corrosion resistance, and thermal
diffusivity [
81
]. Certain CPCMs incorporate nanofillers like graphite, graphene oxide (GO),
and hexagonal boron nitride (HBN), which significantly augment the thermal properties
of the PCM, thereby benefiting solar energy storage systems [
137
]. Additionally, CPCMs
with additives or nanoparticles such as expanded graphite (EG) and carbon fiber (CF)
exhibit favorable thermochemical properties, high thermal conductivity, and remarkable
heat storage capacity [44].
Nanoparticles, characterized by their dimensions smaller than 100 nm, exhibit thermal
conductivity influenced by several factors such as concentration, temperature, particle size,
pH, shape, material composition, and potentially the manufacturing process [
1
]. The litera-
ture highlights diverse methods for synthesizing nanoparticles from disposable materials,
as delineated in Table 4. However, exploring the feasibility of producing nanoparticles from
waste materials remains relatively unexplored. Conversely, limited research delves into the
cost-effectiveness of incorporating nanoparticles in PCM preparation, particularly regard-
ing implementation expenses for specific applications. While some studies demonstrate
the enhancement of PCM thermal conductivity by adding expanded graphite or graphite
nanoparticles, it is noteworthy that this augmentation affects thermal conductivity, melting
time, and overall thermal performance positively [138–140].
Table 4. Nanoparticles consisting of industrial waste materials [141].
Author Waste Materials Nanoparticle
Hu et al. [142] Waste plastic bags Carbon nanoparticles
Hassan et al. [143] Eggshell powder Biobased calcium carbonate nanoparticles
Biswas et al. [144] Waste iron Magnetic iron oxide nanoparticles
Rajarao et al. [145] Silicon dioxide and electronic waste compact discs Silicon carbide nanoparticles
Rangari et al. [146] Egg, mussel, and quahog shells Biobased nanoparticles
D’Oliveira et al. [
141
] demonstrated the capacity of highly conductive nanoparticles
to augment the thermal conductivity of PCM with low melting temperatures (ranging
from 20 to 70
◦
C). The literature underscores the potential of carbon-based nanoparticles
to supplant conventional metallic nanoparticles due to their commendable stability and
ability to enhance PCM thermal conductivity [
45
,
147
,
148
]. In comparison, H.M Teamah and
M. Teamah [
149
] agree on carbon-based nanoparticles but indicate that metallic foams are
also strong candidates. In a study by Cabeza et al. [
150
], a CPCM comprising 10% volume
Energies 2024,17, 2350 17 of 35
of graphite and 90% volume of sodium acetate was investigated for hot water generation.
Their findings revealed that employing this CPCM could extend the duration of hot water
availability, contingent upon the number of bottles used. Although their study assessed
2, 4, and 6 bottles, it clarified that the energy storage density surged to 40%, 57.2%, and
66.7%, respectively.
In contrast, Xie et al. [
151
] present a study demonstrating the feasibility of utilizing
environmentally sustainable materials in creating CPCMs. They employed coconut shell
charcoal (CSC) as the primary material in their investigation. Focused on optimizing the
PCM charging process, they augmented the PCM with CSC, modified the supporting mate-
rial (H
2
O
2
), and evaluated its thermal characteristics in domestic solar energy applications.
Their findings revealed that the CPCM exhibited a nearly threefold increase in thermal
conductivity compared to non-CSC variants. Moreover, the CPCM displayed altered phase
change temperatures, reduced latent heat, and improved efficiency. Furthermore, they
evaluated the material’s performance in a tankless solar water heater, demonstrating its
ability to store energy for subsequent use after sunset effectively. Additional significant
studies are cataloged in Table 5.
Table 5. Research covering composite phase change materials in the literature.
Author PCM/Nanoparticle/HTF Type Study 1Heat Exchanger Results
Haillot et al. [152]RT65/Compressed expanded natural
graphite (CENG)/H2ON/E Flat plate solar collector
•The system’s efficiency is maximized during the summer
compared to the winter.
•Adding the CPCM can maximize the benefits to the system
despite the winter losses.
Sadiq et al. [153]Paraffin/Hybrid nanoparticle of CuO y
Al2O3/H2ON/E Triplex tube heat storage
•By increasing the inlet temperature, the melting time
decreases; the same happens when the mass flow rate of the
system is increased.
•Increasing the fraction of nano-additives
(0.4–3.2%) can reduce the system’s charging period (10–19%,
respectively).
•Theoretical efficiency also increases with increasing
inlet temperature.
Nedjem et al. [55]1-tetradecanol/Graphene nanoplatelets
(GNP)/H2ON Shell and Tube Latent Thermal Storage Unit
•The melting time is reduced at higher GNP concentrations.
•In the discharge process, the solidification time decreases at
lower GNP amounts.
•The stored energy decreases with increasing
nanoparticle concentration.
Mandal et al. [154]Paraffin/Nano-cupric oxide (CuO)
nanoparticles/H2ON Flat plate solar collector
•CPCM can efficiently increase heat transfer by its
thermal conductivity.
•Adding the nanoparticles in PCM enhanced the thermal
conductivity and thermal diffusivity.
Gorzin et al. [155] RT50/Coopernanoparticles/H2O N Multi-shell and tube exchanger
•Nanoparticles significantly reduce the solidification time.
•
Increasing the mass fraction of Cu can enhance the reduction
of solidification time.
Al-Kayiem et al. [156] Paraffin wax/Cooper nanoparticles/H2O E Flat plate solar collector with built-in TES
•
The system’s performance using a 10
◦
collector tilt angle and
nanoparticles enhanced by 0.9% compared to PCM alone
after 24 h. However, they recommend experimenting with
various flow rates.
1Type of study: N = numerical and E = experimental.
This approach can be combined with other methodologies like microencapsulation,
thereby augmenting the thermal characteristics of the PCM and promoting uniform tem-
perature dispersion [
157
]. The utilization of CPCMs is highly prevalent in hot water
generation. Consequently, there is a proposition to fabricate CPCMs incorporating nanopar-
ticles sourced from both organic and inorganic waste materials. Despite the extensive
literature review, only limited instances of CPCMs formulated from organic waste have
been identified. Moreover, no numerical or experimental studies have been encountered
that validate their application in LHTESS.
It is important to acknowledge that this observation might stem from the relatively low
conductivity of these materials, unlike the case with metallic nanoparticles. However, this
inference remains speculative due to the absence of supporting studies. A thorough exami-
nation of the literature reveals that most authors have primarily combined nanoparticles
with paraffin waxes. This highlights a potential way for further investigation to explore the
utilization of nanoparticles with alternative PCMs. Such exploration could yield significant
advancements in properties and heat transfer mechanisms.
Energies 2024,17, 2350 18 of 35
4.1.7. Multiple PCMs (M-PCMs) or Cascade LHTES System
TES systems employing M-PCMs offer a promising solution to mitigate thermal distortion
during the charging and discharging phases. Numerous studies suggest that these systems
can significantly improve efficiency and expedite charging processes, contingent upon the
specific thermal properties of the PCMs used, such as the phase change temperature, latent
heat, thermal conductivity, and mass ratio [
158
,
159
]. Therefore, carefully selecting materials
is imperative to realize performance enhancements [
160
]. This advancement can potentially
optimize heat transfer during latent heat storage periods, offering superior efficiency and
flexibility in energy storage and delivery [160–162]. The position of PCMs within the system
is dictated by their respective melting temperatures, as illustrated in Figure 13. As depicted in
Figure 13a, for heat storage, PCMs should be positioned in decreasing order along the flow
direction of the HTF, while during discharge, the HTF flows in the opposite direction [
158
].
Figure 13b showcases various shapes applicable to U-tube TES systems, demonstrating
potential up to 30% enhancements in the charging process [163].
Paraffin waxes (such as paraffin wax, RT60, and others) and fatty acids (including
myristic acid, stearic acid, lauric acid, and others) are commonly used for energy storage.
Moreover, several studies have carried out investigations using two to five PCMs to achieve
expedited charging and discharging cycles and heightened thermal storage efficiency [
48
].
However, it is worth noting that a study suggests a limit of three stages, as stages after this
threshold produce negligible performance improvements [164].
One notable study employing this technique is conducted by Wang et al. [
165
], wherein
an experimental investigation involving a cylindrical capsule with three distinct PCMs
(stearic acid, paraffin, and lauric acid) demonstrates that employing a cascade system can
augment both the charging period and velocity. Similarly, Mazman et al. [
166
] explore the
utilization of three CPCMs (paraffin–palmitic acid, paraffin–stearic acid, and stearic acid–
myristic acid) and report favorable outcomes regarding the average water temperature
throughout the full charging cycle of a storage tank. They note that during the tank’s
complete discharging phase, the average water temperature remains below the PCM’s flow
temperature, with the stearic acid–paraffin CPCM exhibiting superior thermal performance.
Conversely, Lim et al. [
167
] show findings from their experimental study, highlighting a
28% increase in thermal performance when employing two distinct PCMs within a storage
unit compared to just using one.
Energies 2024, 17, x FOR PEER REVIEW 19 of 38
explore the utilization of nanoparticles with alternative PCMs. Such exploration could
yield significant advancements in properties and heat transfer mechanisms.
4.1.7. Multiple PCMs (M-PCMs) or Cascade LHTES System
TES systems employing M-PCMs offer a promising solution to mitigate thermal dis-
tortion during the charging and discharging phases. Numerous studies suggest that these
systems can significantly improve efficiency and expedite charging processes, contingent
upon the specific thermal properties of the PCMs used, such as the phase change temper-
ature, latent heat, thermal conductivity, and mass ratio [158,159]. Therefore, carefully se-
lecting materials is imperative to realize performance enhancements [160]. This advance-
ment can potentially optimize heat transfer during latent heat storage periods, offering
superior efficiency and flexibility in energy storage and delivery [160–162]. The position
of PCMs within the system is dictated by their respective melting temperatures, as illus-
trated in Figure 13. As depicted in Figure 13a, for heat storage, PCMs should be positioned
in decreasing order along the flow direction of the HTF, while during discharge, the HTF
flows in the opposite direction [158]. Figure 13b showcases various shapes applicable to
U-tube TES systems, demonstrating potential up to 30% enhancements in the charging
process [163].
(a) (b)
Figure 13. Operation of energy storage for various phase change materials by (a) Christopher et al.
[158] (Copyright © 2021 Elsevier Ltd.); (b) Kurnia et al. [163] (Copyright © 2012 Elsevier Ltd.).
Paraffin waxes (such as paraffin wax, RT60, and others) and fay acids (including
myristic acid, stearic acid, lauric acid, and others) are commonly used for energy storage.
Moreover, several studies have carried out investigations using two to five PCMs to
achieve expedited charging and discharging cycles and heightened thermal storage effi-
ciency [48]. However, it is worth noting that a study suggests a limit of three stages, as
stages after this threshold produce negligible performance improvements [164].
One notable study employing this technique is conducted by Wang et al. [165],
wherein an experimental investigation involving a cylindrical capsule with three distinct
PCMs (stearic acid, paraffin, and lauric acid) demonstrates that employing a cascade sys-
tem can augment both the charging period and velocity. Similarly, Mazman et al. [166]
explore the utilization of three CPCMs (paraffin–palmitic acid, paraffin–stearic acid, and
stearic acid–myristic acid) and report favorable outcomes regarding the average water
temperature throughout the full charging cycle of a storage tank. They note that during
the tanks complete discharging phase, the average water temperature remains below the
PCMs flow temperature, with the stearic acid–paraffin CPCM exhibiting superior thermal
performance. Conversely, Lim et al. [167] show findings from their experimental study,
highlighting a 28% increase in thermal performance when employing two distinct PCMs
within a storage unit compared to just using one.
Figure 13. Operation of energy storage for various phase change materials by (a) Christopher et al. [
158
]
(Copyright © 2021 Elsevier Ltd.); (b) Kurnia et al. [163] (Copyright © 2012 Elsevier Ltd.).
Khor et al. [
168
] investigated the charging process of three different PCMs configura-
tions, revealing a reduction in charging time with this setup. Their findings underscore
an effective arrangement for positioning various PCMs within a LHTESS. Conversely,
Pu et al. [169]
conducted a numerical study, corroborated by experimental validation, to as-
sess whether employing M-PCMs could augment heat transfer efficiency and expedite PCM
melting. Their investigation employed a shell-and-tube TES unit featuring three PCMs
Energies 2024,17, 2350 19 of 35
arranged radially alongside copper foam. A comparison was drawn with the utilization
of a single PCM. Contrary to expectations, the results indicated that employing M-PCMs
did not yield significantly higher HTE compared to using a single PCM. Additionally, the
authors suggested optimizing thermal performance by adjusting the porosity distribution
within the copper foam.
In this technique, careful PCM selection is imperative, as the integration of cascading
PCMs that do not contribute to smooth heat transfer may adversely impact the system’s
HTE. Hence, consideration of the thermal properties of the PCM is vital in this regard. It is
noteworthy that, for the effective implementation of this method, PCMs with phase change
temperatures not surpassing 60
◦
C are recommended. However, this recommendation
depends on the prevailing climatic conditions in the desired hot water generation setting,
as it necessitates a progressive phase change within the system. Numerous experimental
studies validating HTE were identified for this technique, involving blending various
PCMs such as fatty acids and paraffin waxes or using only paraffin waxes. Furthermore,
it was observed that while this technique is commonly employed in TES tanks, it is less
prevalent in solar collectors or shell-and-tube TES units. Determination of the optimal
quantity of PCM modules for this technique is crucial, as divergent opinions exist regarding
the maximum amount of PCMs to be employed.
4.1.8. Coils
Based on previous observations, researchers tend to prioritize the augmentation of sur-
face area in storage systems. Hence, one viable approach is adopting coil or spiral/helical
tube configurations. Such arrangements can potentially improve system performance,
elevate energy efficiency, and decrease the PCM’s melting duration [170].
Based on the investigation conducted by Rogowski and Andrzejczyk [
95
], various
research studies are delving into the coil geometry to augment the solidification and melting
characteristics of PCMs. Primarily experimental, these studies predominantly focus on
low-temperature PCMs, commonly employed in hot water generation. Figure 14 illustrates
some examples of used coils, while Table 6presents a compilation of research efforts
concerning coil utilization in LHTESS.
Energies 2024, 17, x FOR PEER REVIEW 20 of 38
Khor et al. [168] investigated the charging process of three different PCMs configura-
tions, revealing a reduction in charging time with this setup. Their findings underscore an
effective arrangement for positioning various PCMs within a LHTESS. Conversely, Pu et
al. [169] conducted a numerical study, corroborated by experimental validation, to assess
whether employing M-PCMs could augment heat transfer efficiency and expedite PCM
melting. Their investigation employed a shell-and-tube TES unit featuring three PCMs
arranged radially alongside copper foam. A comparison was drawn with the utilization
of a single PCM. Contrary to expectations, the results indicated that employing M-PCMs
did not yield significantly higher HTE compared to using a single PCM. Additionally, the
authors suggested optimizing thermal performance by adjusting the porosity distribution
within the copper foam.
In this technique, careful PCM selection is imperative, as the integration of cascading
PCMs that do not contribute to smooth heat transfer may adversely impact the systems
HTE. Hence, consideration of the thermal properties of the PCM is vital in this regard. It
is noteworthy that, for the effective implementation of this method, PCMs with phase
change temperatures not surpassing 60 °C are recommended. However, this recommen-
dation depends on the prevailing climatic conditions in the desired hot water generation
seing, as it necessitates a progressive phase change within the system. Numerous exper-
imental studies validating HTE were identified for this technique, involving blending var-
ious PCMs such as fay acids and paraffin waxes or using only paraffin waxes. Further-
more, it was observed that while this technique is commonly employed in TES tanks, it is
less prevalent in solar collectors or shell-and-tube TES units. Determination of the optimal
quantity of PCM modules for this technique is crucial, as divergent opinions exist regard-
ing the maximum amount of PCMs to be employed.
4.1.8. Coils
Based on previous observations, researchers tend to prioritize the augmentation of
surface area in storage systems. Hence, one viable approach is adopting coil or spiral/hel-
ical tube configurations. Such arrangements can potentially improve system performance,
elevate energy efficiency, and decrease the PCMs melting duration [170].
Based on the investigation conducted by Rogowski and Andrzejczyk [95], various
research studies are delving into the coil geometry to augment the solidification and melt-
ing characteristics of PCMs. Primarily experimental, these studies predominantly focus
on low-temperature PCMs, commonly employed in hot water generation. Figure 14 illus-
trates some examples of used coils, while Table 6 presents a compilation of research efforts
concerning coil utilization in LHTESS.
(a) (b) (c)
Energies 2024, 17, x FOR PEER REVIEW 21 of 38
(d)
Figure 14. Different geometries coils. (a) Simple helicoidal coil; (b) non-equidistantly spaced helical
coil; (c) helical coil with a variable pitch; (d) complex helicoidal coils, red (hot fluid) and blue (cold
fluid) [95] (CC by 4.0).
This approach circumvents health concerns by averting direct contact between the
PCM or any fluid and the HTF within LHTESS. Its applicability extends to SHTS systems,
ensuring the storage material remains isolated from the HTF. Multiple experimental in-
vestigations in this methodology corroborate its efficacy in enhancing heat transfer, albeit
most of these studies are conducted at the laboratory scale. Therefore, validating this tech-
nique for hot water generation in real-world scenarios is advisable to ascertain its potential
for efficiently improving heat transfer in such systems.
4.1.9. Nanofluids
Nanofluids offer distinct advantages in solar systems or collectors compared to tra-
ditional fluids. They can augment heat transfer rates and find utility across various appli-
cations [171,172]. Nanofluids are derived from nanoparticles (Al, Au, Ag, Cu) with sizes
below 100 nm dispersed in water or other fluids [173]. Hybrid nanofluids are also preva-
lent, containing two types of nanoparticles within a fluid. Employing stable hybrid
nanofluids with reduced viscosity and heightened thermal conductivity can elevate the
efficacy of solar collectors [1]. These fluids serve as a potential alternative to enhance heat
transfer efficiency in PCMs, alter thermal conductivity, boost the effectiveness of heat stor-
age systems, or serve as substitutes for HTF [106,174]. Nanofluids can be integrated with
other methodologies like encapsulations or used independently to amplify the thermal
performance of solar collectors [1,108,175–177].
Table 6. Use of coil in latent heat storage systems according to the literature.
Aut ho r Type of
Study 1 Overview
Kabbara
et al. [42] E
The systems performance was analyzed by incorporating a helical coil into a storage tank with lauric acid
PCM. Temperature variations were notable during charging and discharging. However, the authors empha-
size the need to explore different coil geometries and flow rates to fully grasp the systems dynamics.
Anish et
al. [178] E
Using a double helix coil consisting of a tube, a significant difference in the temperatures of the top and bot-
tom of the tank was obtained in the melting process. Moreover, the solidification process occurred uniformly
in the tank.
Korti and
Tle ms ani
[179]
E
Using a copper helical coil with various PCM types, charging temperatures and flow rates revealed a higher
efficiency during the charging process compared to discharging. This discrepancy is due to convection domi-
nance during melting. Additionally, charging temperatures notably impacted the results.
Dinker et
al. [180] E
A study was conducted in a rectangular storage tank with PCM (beeswax) and HTF (water) flowing in a heli-
cal coil with different temperatures and flow rates. Their results show that temperature can significantly influ-
ence the efficiency of the solidification and melting processes.
Saydam et
al. [181] E
A study investigated the solidification and melting processes of a PCM (Paraffin wax) in a storage tank with a
helical coil. Findings revealed faster melting of the PCM on the tanks periphery and slower near the axis dur-
ing both processes. However, the authors suggest adding more coils at the tanks boom for improved dis-
charge efficiency. It was found that the flow direction of the HTF (ethylene glycol (EG)–water mixture) had a
Figure 14. Different geometries coils. (a) Simple helicoidal coil; (b) non-equidistantly spaced helical
coil; (c) helical coil with a variable pitch; (d) complex helicoidal coils, red (hot fluid) and blue (cold
fluid) [95] (CC by 4.0).
Energies 2024,17, 2350 20 of 35
This approach circumvents health concerns by averting direct contact between the
PCM or any fluid and the HTF within LHTESS. Its applicability extends to SHTS systems,
ensuring the storage material remains isolated from the HTF. Multiple experimental inves-
tigations in this methodology corroborate its efficacy in enhancing heat transfer, albeit most
of these studies are conducted at the laboratory scale. Therefore, validating this technique
for hot water generation in real-world scenarios is advisable to ascertain its potential for
efficiently improving heat transfer in such systems.
4.1.9. Nanofluids
Nanofluids offer distinct advantages in solar systems or collectors compared to tra-
ditional fluids. They can augment heat transfer rates and find utility across various ap-
plications [
171
,
172
]. Nanofluids are derived from nanoparticles (Al, Au, Ag, Cu) with
sizes below 100 nm dispersed in water or other fluids [
173
]. Hybrid nanofluids are also
prevalent, containing two types of nanoparticles within a fluid. Employing stable hybrid
nanofluids with reduced viscosity and heightened thermal conductivity can elevate the
efficacy of solar collectors [
1
]. These fluids serve as a potential alternative to enhance
heat transfer efficiency in PCMs, alter thermal conductivity, boost the effectiveness of heat
storage systems, or serve as substitutes for HTF [
106
,
174
]. Nanofluids can be integrated
with other methodologies like encapsulations or used independently to amplify the thermal
performance of solar collectors [1,108,175–177].
Table 6. Use of coil in latent heat storage systems according to the literature.
Author Type of Study 1Overview
Kabbara et al. [42] E
The system’s performance was analyzed by incorporating a helical coil into a storage tank with lauric acid PCM.
Temperature variations were notable during charging and discharging. However, the authors emphasize the
need to explore different coil geometries and flow rates to fully grasp the system’s dynamics.
Anish et al. [178] E
Using a double helix coil consisting of a tube, a significant difference in the temperatures of the top and bottom of
the tank was obtained in the melting process. Moreover, the solidification process occurred uniformly in the tank.
Korti and Tlemsani [179] E Using a copper helical coil with various PCM types, charging temperatures and flow rates revealed a higher
efficiency during the charging process compared to discharging. This discrepancy is due to convection
dominance during melting. Additionally, charging temperatures notably impacted the results.
Dinker et al. [180] E A study was conducted in a rectangular storage tank with PCM (beeswax) and HTF (water) flowing in a helical
coil with different temperatures and flow rates. Their results show that temperature can significantly influence
the efficiency of the solidification and melting processes.
Saydam et al. [181] E
A study investigated the solidification and melting processes of a PCM (Paraffin wax) in a storage tank with a
helical coil. Findings revealed faster melting of the PCM on the tank’s periphery and slower near the axis during
both processes. However, the authors suggest adding more coils at the tank’s bottom for improved discharge
efficiency. It was found that the flow direction of the HTF (ethylene glycol (EG)–water mixture) had a negligible
impact on the charging and discharging period but did influence the temperature fluctuations of the PCM within
the energy storage unit.
Rahimi et al. [182] E The impact of charging temperature on the coil storage tank’s performance was assessed alongside the
introduction of a dimensionless parameter known as the Stefan number. The findings indicate that a specific
Stefan number can decrease the PCM’s melting time.
1Type of study: E = experimental.
Using nanofluids in solar systems offers several advantages, including reducing the
required heat transfer area, high density, conductivity, and thermal properties, along
with favorable optical characteristics and stability [
183
]. When combined with PCMs
possessing good HTE and thermal stability, nanofluids can extend operational time and
decrease energy consumption [
184
]. However, their main disadvantages include high
costs, thermal instability, chemical compatibility issues, and complexities in the manu-
facturing process [
183
]. Over the years, nanofluid technology has advanced, as depicted
in
Figures 15 and 16,
showcasing the diverse fluids and nanoparticles used in preparing
nanofluids or hybrid nanofluids. Commonly employed nanoparticles in solar collectors en-
compass CeO
2
, SiO
2
, Al
2
O
3
, CuO, graphene, and TiO
2
[
4
,
17
,
108
,
185
]. Additionally, carbon-
based nanomaterials exhibit superior thermal conductivity for such applications [
141
,
176
].
Nonetheless, a primary challenge lies in selecting appropriate nanoparticles and fluids for
specific applications [
52
]. Aggarwal et al. [
17
] have demonstrated that PCMs and nanoflu-
ids can synergize to enhance heat transfer in solar water heaters, including evacuated tube
Energies 2024,17, 2350 21 of 35
solar collectors (ETSCs) and flat plate solar collectors (FPSCs), leveraging the manifold
advantages offered by nanofluids.
Energies 2024, 17, x FOR PEER REVIEW 22 of 38
negligible impact on the charging and discharging period but did influence the temperature fluctuations of
the PCM within the energy storage unit.
Rahimi et
al. [182] E
The impact of charging temperature on the coil storage tanks performance was assessed alongside the intro-
duction of a dimensionless parameter known as the Stefan number. The findings indicate that a specific Stefan
number can decrease the PCMs melting time.
1 Type of study: E = experimental.
Using nanofluids in solar systems offers several advantages, including reducing the
required heat transfer area, high density, conductivity, and thermal properties, along with
favorable optical characteristics and stability [183]. When combined with PCMs pos-
sessing good HTE and thermal stability, nanofluids can extend operational time and de-
crease energy consumption [184]. However, their main disadvantages include high costs,
thermal instability, chemical compatibility issues, and complexities in the manufacturing
process [183]. Over the years, nanofluid technology has advanced, as depicted in Figures
15 and 16, showcasing the diverse fluids and nanoparticles used in preparing nanofluids
or hybrid nanofluids. Commonly employed nanoparticles in solar collectors encompass
CeO2, SiO2, Al2O3, CuO, graphene, and TiO2 [4,17,108,185]. Additionally, carbon-based na-
nomaterials exhibit superior thermal conductivity for such applications [141,176]. None-
theless, a primary challenge lies in selecting appropriate nanoparticles and fluids for spe-
cific applications [52]. Aggarwal et al. [17] have demonstrated that PCMs and nanofluids
can synergize to enhance heat transfer in solar water heaters, including evacuated tube
solar collectors (ETSCs) and flat plate solar collectors (FPSCs), leveraging the manifold
advantages offered by nanofluids.
Figure 15. Published articles about nanofluids in the literature by Muhamude et al. [1] (CC by 4.0).
Figure 16. Different nanoparticles and fluids used to create hybrid nanofluids [1] (CC by 4.0).
Figure 15. Published articles about nanofluids in the literature by Muhamude et al. [1] (CC by 4.0).
Energies 2024, 17, x FOR PEER REVIEW 22 of 38
negligible impact on the charging and discharging period but did influence the temperature fluctuations of
the PCM within the energy storage unit.
Rahimi et
al. [182] E
The impact of charging temperature on the coil storage tanks performance was assessed alongside the intro-
duction of a dimensionless parameter known as the Stefan number. The findings indicate that a specific Stefan
number can decrease the PCMs melting time.
1 Type of study: E = experimental.
Using nanofluids in solar systems offers several advantages, including reducing the
required heat transfer area, high density, conductivity, and thermal properties, along with
favorable optical characteristics and stability [183]. When combined with PCMs pos-
sessing good HTE and thermal stability, nanofluids can extend operational time and de-
crease energy consumption [184]. However, their main disadvantages include high costs,
thermal instability, chemical compatibility issues, and complexities in the manufacturing
process [183]. Over the years, nanofluid technology has advanced, as depicted in Figures
15 and 16, showcasing the diverse fluids and nanoparticles used in preparing nanofluids
or hybrid nanofluids. Commonly employed nanoparticles in solar collectors encompass
CeO2, SiO2, Al2O3, CuO, graphene, and TiO2 [4,17,108,185]. Additionally, carbon-based na-
nomaterials exhibit superior thermal conductivity for such applications [141,176]. None-
theless, a primary challenge lies in selecting appropriate nanoparticles and fluids for spe-
cific applications [52]. Aggarwal et al. [17] have demonstrated that PCMs and nanofluids
can synergize to enhance heat transfer in solar water heaters, including evacuated tube
solar collectors (ETSCs) and flat plate solar collectors (FPSCs), leveraging the manifold
advantages offered by nanofluids.
Figure 15. Published articles about nanofluids in the literature by Muhamude et al. [1] (CC by 4.0).
Figure 16. Different nanoparticles and fluids used to create hybrid nanofluids [1] (CC by 4.0).
Figure 16. Different nanoparticles and fluids used to create hybrid nanofluids [1] (CC by 4.0).
Figure 17 displays various models for simulating nanofluids, with the mixture model
being the most prevalent due to its ability to simulate different velocities across phases
and its applicability in interpenetrating phases [
186
]. Solar collectors are commonly
used for low-temperature systems, particularly in hot water generation [
187
]. Figure 18
showcases examples of solar collectors in the literature, providing insight into where
nanofluids have been employed for enhancement. Subsequently, this paper will outline
research conducted with nanofluids in solar collectors, structured into three sections to
facilitate comprehension.
Energies 2024, 17, x FOR PEER REVIEW 23 of 38
Figure 17 displays various models for simulating nanofluids, with the mixture model
being the most prevalent due to its ability to simulate different velocities across phases
and its applicability in interpenetrating phases [186]. Solar collectors are commonly used
for low-temperature systems, particularly in hot water generation [187]. Figure 18 show-
cases examples of solar collectors in the literature, providing insight into where nanofluids
have been employed for enhancement. Subsequently, this paper will outline research con-
ducted with nanofluids in solar collectors, structured into three sections to facilitate com-
prehension.
Figure 17. Different approaches are used to simulate nanofluids in various applications [69] (Copy-
right © 2022 Elsevier Ltd.).
(a) (b) (c)
Figure 18. Types of solar collectors: (a) flat plate solar collector [188] (Copyright © 2010 Elsevier
Ltd.); (b) evacuated tube solar collectors [189] (Copyright © 2016 Elsevier Ltd.); (c) photovoltaic/ther-
mal solar collector [190] (Copyright © 2016 Elsevier B.V.).
1. Flat plate solar collectors (FPSCs)
Using PCMs in FPSCs can extend hot water availability and enhance system effi-
ciency. However, outcomes are contingent on factors such as the degree of inclination,
PCM–collector contact, solar radiation, and thermal stratification in the storage tank [191].
FPSCs are frequently employed in research due to their accessibility and affordability,
leading to numerous studies aimed at improving heat transfer (via nanofluids), maintain-
ing stable temperatures (with PCMs), or enhancing system thermal capacity (through
nanofluid–PCM integration) [177,184]. Table 7 presents a selection of studies conducted
with FPSCs.
Figure 17. Different approaches are used to simulate nanofluids in various applications [
69
]
(Copyright © 2022 Elsevier Ltd.).
Energies 2024,17, 2350 22 of 35
Energies 2024, 17, x FOR PEER REVIEW 23 of 38
Figure 17 displays various models for simulating nanofluids, with the mixture model
being the most prevalent due to its ability to simulate different velocities across phases
and its applicability in interpenetrating phases [186]. Solar collectors are commonly used
for low-temperature systems, particularly in hot water generation [187]. Figure 18 show-
cases examples of solar collectors in the literature, providing insight into where nanofluids
have been employed for enhancement. Subsequently, this paper will outline research con-
ducted with nanofluids in solar collectors, structured into three sections to facilitate com-
prehension.
Figure 17. Different approaches are used to simulate nanofluids in various applications [69] (Copy-
right © 2022 Elsevier Ltd.).
(a) (b) (c)
Figure 18. Types of solar collectors: (a) flat plate solar collector [188] (Copyright © 2010 Elsevier
Ltd.); (b) evacuated tube solar collectors [189] (Copyright © 2016 Elsevier Ltd.); (c) photovoltaic/ther-
mal solar collector [190] (Copyright © 2016 Elsevier B.V.).
1. Flat plate solar collectors (FPSCs)
Using PCMs in FPSCs can extend hot water availability and enhance system effi-
ciency. However, outcomes are contingent on factors such as the degree of inclination,
PCM–collector contact, solar radiation, and thermal stratification in the storage tank [191].
FPSCs are frequently employed in research due to their accessibility and affordability,
leading to numerous studies aimed at improving heat transfer (via nanofluids), maintain-
ing stable temperatures (with PCMs), or enhancing system thermal capacity (through
nanofluid–PCM integration) [177,184]. Table 7 presents a selection of studies conducted
with FPSCs.
Figure 18. Types of solar collectors: (a) flat plate solar collector [
188
] (Copyright © 2010 Elsevier Ltd.);
(b) evacuated tube solar collectors [
189
] (Copyright © 2016 Elsevier Ltd.); (c) photovoltaic/thermal
solar collector [190] (Copyright © 2016 Elsevier B.V.).
1. Flat plate solar collectors (FPSCs)
Using PCMs in FPSCs can extend hot water availability and enhance system effi-
ciency. However, outcomes are contingent on factors such as the degree of inclination,
PCM–collector
contact, solar radiation, and thermal stratification in the storage tank [
191
].
FPSCs are frequently employed in research due to their accessibility and affordability,
leading to numerous studies aimed at improving heat transfer (via nanofluids), main-
taining stable temperatures (with PCMs), or enhancing system thermal capacity (through
nanofluid–PCM integration) [
177
,
184
]. Table 7presents a selection of studies conducted
with FPSCs.
Table 7. Studies on the use of nanofluids in flat plate solar collectors.
Author Nanofluid Based on Type of Study Results
Kunwer et al. [172] Titanium dioxide (TiO2)/Therminol Numerical/Experimental
■It increases the thermal efficiency and
friction factor by 4% of the TiO2proportion.
■The thermal efficiency can be increased
depending on the working fluid as used
and the Reynolds number increase.
Ahmadlouydarab et al. [192] TiO2/Purified water Lab-scale
■
Significant increase in efficiency for different
volume fractions of TiO2nanoparticles
(0.1% to 5%). For a volume fraction of 5%,
there was an efficiency increase of 45%.
■
Increased volume fraction allowed for better
heat absorption.
Said et al. [193] Al2O3/H2O Experimental
■Fifty percent increase in heat transfer
coefficient for nanoparticle concentrations
of 0.1 and 0.3% by volume (size 13 nm).
■At a mass flow rate of 1.5 kg/min, energy
efficiency can be increased to 83.5%.
Chaji et al. [194] TiO2/H2O Experimental
■Nanoparticles enhanced efficiency
compared to the base fluid.
■Efficiency decreases with increasing mass
flow rate.
2 Evacuated tube solar collectors (ETSCs)
ETSCs feature parallel tubes designed to withstand reflection and absorb high so-
lar radiation with specialized glass coatings, enhancing efficiency, thermal conductivity,
and energy storage [
177
,
195
]. Hence, they are extensively employed in domestic applica-
tions [
196
]. As of 2020, thermosyphon-type ETSCs are the most commonly utilized [
183
].
Table 8showcases notable studies conducted with ETSCs.
3 Photovoltaic–thermal collectors
Kezemian et al. [
197
] conducted a 3D numerical study to enhance solar collector
performance using various hybrid nanofluids: MWCNT–aluminum oxide, MWCNT–silicon
carbide, graphene–aluminum oxide, and graphene–silicon carbide. Their findings reveal
that the MWCNT–silicon carbide hybrid nanofluid exhibits superior electrical and thermal
Energies 2024,17, 2350 23 of 35
energy efficiency compared to others. Similarly, Khodadadi and Sheikholeslami [
198
]
demonstrated that incorporating nanoparticles such as MWCNT, SiC, Cu, Ag, Al
2
O
3
, and
ZnO in water and PCM boosts the charging rate while marginally reducing unit and
coolant temperatures. Additionally, they observed changes in the PCM’s liquid fraction
with alterations in the system’s flow rate.
Table 8. Studies on the use of nanofluids in evacuated tube solar collectors.
Author Nanofluid Based on Type of Study 1Results
Tabarhoseini et al. [199] Nanoparticles of CuO/pure H2O N
■Irreversibility of heat transfer caused sudden
increases in fluid viscosity and pressure change.
■Nano-sized powders within the fluid
are suspended.
■Entropy generation decreased by 6.3% with the
use of nanofluids.
Ghaderian et al. [200] Nanoparticles of CuO/H2O E
■At a volume concentration of 0.05% of
nanoparticles and a flow rate of 60 l/h, efficiency
increased by 51.4%. This boost stemmed from
heightened thermal conductivity attributable to
the nanoparticles’ high density.
Al-Mashat and Hasan et al. [201] Al2O3/water N/E
■If the volume fraction of Al2O3increases, the
efficiency can increase proportionally.
■The recommended angle of inclination of the
evacuated tube is 41◦annually.
Eltaweel et al. [196] MWCNT/water E
■
Increased flow rate and nanofluid concentrations
can increase efficiencies.
Mahbubul et al. [202]Single-walled carbon nanotubes
(SWCNT)/water E■Efficiency increased by almost 10%.
Daghigh and Zandi [203]water/TiO2, water/CuO and
water/MWCNT T/E
■A nanofluid composite with MWCNT
nanoparticles obtained a higher
performance increase.
Kumar and Kaushal [204]Nanoparticles of graphene- ethylene
glycol/water E
■
Variations in graphene concentrations revealed a
proportional increase in thermal conductivity
and efficiency, particularly evident when fluid
inlet temperature aligns with
ambient conditions.
Ghaderian and Sidik [205] Al2O3/distilled water E
■The collector’s efficiency rises with nanofluid
use, further increasing with higher volume
fractions of nanoparticles.
1Type of study: N = numerical, T = theorical, and E = experimental.
In conclusion, passive methods, including nanofluids, encapsulation, fins, M-PCMs,
and porous media, are deemed most effective for hot water generation applications. Among
these, fins are considered practical, especially with simple configurations during system
installation. Additionally, M-PCMs are seen as advantageous when proper PCM selection
is used. These techniques are commonly employed due to their low costs, except for
nanofluids, which incur higher manufacturing costs. However, it is essential to note that
the literature does not have data on the construction, creation, or operational costs of
these methods in energy storage systems; thus, our perspective is solely based on selected
document readings.
4.2. Active Methods
Active methods, unlike passive ones, employ external sources or auxiliary tools to
enhance heat transfer [
69
]. Shank and Tiari [
46
] highlighted various approaches to improve
HTE in PCM systems, such as mechanical aids, vibration, jet impingement, injection, and
external fields. Three of these techniques stand out as potential starting points for further
research in hot water generation. Below are summarized conclusions regarding each
method as indicated by these authors.
•
Mechanical aids, such as rotating cylinders, rotary systems, and scraped surfaces, play
a significant role in the charging and discharging processes of PCM systems, reducing
the solidification time and enhancing heat transfer. However, their use entails complex
Energies 2024,17, 2350 24 of 35
system designs, increased manufacturing and maintenance requirements, and safety
risks due to the constant movement of the liquid PCM during operation.
•
Vibration: Although vibration has shown promise in enhancing PCM fusion during
the charging process, further investigation is needed, particularly regarding its effec-
tiveness during discharge. It is important to note that this technique operates with
high amplitudes and frequencies, posing potential safety risks during operation.
•
External fields: This method introduces a novel approach to improve the thermal
behavior of LHTES systems. However, it may encounter conflicts with system com-
ponents due to the involvement of magnetic, electric, and ultrasonic fields. Further
studies across various fields (electric, magnetic, and ultrasonic) are necessary to deter-
mine its potential for enhancing heat transfer in HWGS with PCMs.
Alternatively, Yan et al. [
8
] performed an experimental investigation employing ultra-
sound to improve heat transfer. Their study aimed to assess the impact of ultrasound on the
charging process of PCMs. Results demonstrated a significant reduction in charging time
(60.69%) and a substantial increase in the heat transfer coefficient (250.97%) at a constant
temperature of 60
◦
C and a flow rate of 3 L/min. Additionally, enhanced natural convection
within the PCM was observed. Thus, ultrasound demonstrates the potential for enhancing
PCM utilization in hot water systems.
A notable disparity in operational cost and safety risk arises when comparing active
and passive methods, particularly without adequate installation measures. Consequently,
many researchers lean towards passive methods, which is evident in the abundance of
results observed in Section 4.1 and this section. However, given the lack of research
validating a fair comparison, investigations with existing setups tailored to active methods
are recommended. This is crucial to ascertain the potential of these methods for residential
or industrial hot water generation. Furthermore, economic studies are essential to evaluate
the long-term benefits of employing active methods, considering the financial investment.
4.3. Hybrid Methods
A hybrid approach combines at least two active or passive techniques, offering po-
tentially higher efficiency than individual methods. Recent studies have underscored the
significance of exploring these hybrid methods [
26
,
72
]. Below, various combined techniques
found in the analysis of this work are presented.
Asgari et al. [
78
] conducted numerical research on fin utilization for improving heat
transfer and PCM solidification, exploring various synthetic forms of Al
2
O
3
-Cu nanoparti-
cles (brick, cylindrical, platelet, and lamina). They concluded that increasing the volume
fraction of hybrid nanoparticles accelerates solidification and enhances heat transfer. The
study suggests that nanoparticles are essential for faster solidification in a finned system.
Conversely, Kazaz et al. [175] demonstrated that nano-encapsulation of paraffin PCM can
boost energy storage, varying efficacy based on the type of nanoparticles used.
Zhu et al. [
206
] propose evaluating the energy storage efficiency of a composite consist-
ing of PCM with metal foam, finned metal foam with graded porosity (PCM-FFGP), and fin.
Their numerical study demonstrates that PCM-FFGP significantly improves system perfor-
mance and reduces the PCM melting time by facilitating the PCM melting sequence with the
fin and enhancing heat transfer between the heat source and PCM through the metal foam.
They suggest that increasing the number of pores per inch may reduce natural convection
heat transfer in PCM-FFGP. Therefore, they recommend a 3% porosity gradient along with
a 5 mm thickness of the fins for better energy storage capacity. Conversely,
Cui et al. [12]
suggest that porous media can achieve higher heat transfer enhancement based on research
conducted until early 2022. Lastly, although the work of
Sathyamurthy et al. [207]
is not
directly related to hot water generation, it suggests a potential application of a hybrid
method by using soda cans encapsulated with black paint and carbon soot nanoparticles
to enhance thermal conductivity and heat absorption of the PCM. Other hybrid methods
from the literature are summarized in Table 9.
Energies 2024,17, 2350 25 of 35
Table 9. Different hybrid methods found in the literature review.
Hybrid Method Author Materials Type Study 3PCM/HTF Results
Fins and nanoparticles
Ghalambaz et al. [208]
Copper fins/GO, Al2O3,
TiO2, Cu and
Ag nanoparticles
NCoconut oil 2
■The shell’s aspect ratio and the fin tilt degree can
significantly influence the charging time.
■Reversing the conical shell shape and incorporating a
4% nanoparticle volume fraction can further improve
charging time.
Nakhchi et al. [209]Stair fins/CuO
nanoparticles NLauric acid 2
■Incorporating PCM with nanoparticles and fins
enhanced heat transfer and melting process efficiency.
■
Nanoparticles augment thermal conductivity,while fins
enhance energy storage capacity.
Nanoparticles and encapsulation Li et al. [210]Sphere glass
shall/aluminum powder E Paraffin/Water Bath
■
The presence of powder sediments facilitates significant
enhancements in thermal conductivity,melting, and
solidification processes, thereby accelerating heat
transfer at the bottom.
■The sphere allows a melting of the material at the top.
Encapsulation and porous media Li et al. [130]
Polystyrene
nanoencapsulation/cooper
metal foam
N/E Octadecane 2
■The metallic foam helps enhance heat transfer through
heat conduction.
■Nano-encapsulation allows for better heat storage.
M-PCMs and fins Asker et al. [211] Aluminum fins N RT30, RT40 and RT50 2■Fin spacing and length play a key role in the melting
time of M-PCMs.
Porous media and nanoparticles
Fan et al. [212]
Melamine
foam/multi-walled carbon
nanotube
N/E
Polyethylene glycol (PEG)
2
■Light absorption is enhanced due to the system’s
output temperature of 79 ◦C.
■Heat storage and efficiency were increased.
■The fins facilitate rapid heat transfer in the CPCM,
enhancing energy storage efficiency by 89.2%. This
surpasses the efficiency of flat plate and
tubular collectors.
Li et al. [213]Cooper
nanoparticles/metal foam NPCM 1/H2O
■Incorporating 5% nanoparticles reduced solidification
and melting times by 25.9% and 28.2%, respectively.
■Introducing 95% porosity further decreased charging
and discharging times by 83.7% and 88.2%, respectively.
■Combining both techniques resulted in negligible time
reductions compared to PM.
Mhiri et al. [214]Graphite
nanoparticles/carbon foam N/E RT60 2
■It improves PCM’s thermal reliability and conductivity
while preventing material leakage and increasing the
melting speed.
Fins, nanoparticles, encapsulation,
and geometry variation Yu et al. [64] Fin/expanded graphite N PCM 1,2
■
The melting time is reduced, and performance increases
when using an inverted conical vessel compared to a
typical cylindrical vessel.
■Combining both vessels (conical and inverted conical)
can enhance heat storage capacity.
1
PCM is not specified/disclosed.
2
HTF is not specified/disclosed.
3
Type of study: N = numerical and
E = experimental.
Combining different techniques in LHTESS can significantly enhance heat transfer
efficiency by improving multiple parameters simultaneously, such as increasing the heat
transfer surface area and the thermal conductivity of the PCM. Table 9highlights various
combinations, with nanoparticles being prevalent in most cases, aligning with the findings
of Asgari et al. [
78
] and underscoring the importance of nanoparticles in systems employ-
ing diverse techniques. Exploring combinations involving more than two techniques or
integrating passive and active techniques presents promising research possibilities for
further investigation.
5. Challenges and Prospective Directions
The review indicates a scarcity of studies focusing on enhancing hot water generation
applications. Nonetheless, this study serves as a guide for advancements in HTE within this
domain. While most HTE investigations in domestic settings center on fins, porous media,
and encapsulation techniques, further research is needed to explore other methods and
their efficacy across different global climates. Moreover, there is a lack of experimental data
documenting the economic and health implications of employing the various techniques
discussed in this paper.
Regarding active methods, only a single study has been undertaken using ultrasound
on a laboratory scale. While its outcomes appear promising, further assessment within a
full-scale system is imperative to ascertain its efficacy in hot water generation. Conversely,
hybrid methods present a broad research method, as numerous combinations of techniques
can be explored, encompassing both passive–passive and passive–active approaches. No-
tably, the literature exploration yielded no information on mixtures of active–active and
passive–active methods.
Energies 2024,17, 2350 26 of 35
Despite the promising potential of nanofluids, further studies are needed to evaluate
their performance under various climatic conditions and to assess their environmental
impact at the end of their lifecycle. These investigations are essential for validating their
use or substitution for traditional refrigerants in solar collectors.
6. Conclusions
This document provides a bibliographic study of numerical, experimental, and laboratory-
scale research on HTE in LHTESS that may be useful for hot water generation through low-
temperature PCMs. Firstly, the bibliometric analysis of the selected documents revealed a
trend over the years towards improving heat transfer in energy storage systems, providing
a global overview of the topic. Additionally, extensive research by academic institutions
and predominant article publications in Asian countries was observed. Despite the selected
documents being related to PCMs and domestic hot water, there was limited connection
with solar energy or solar water heaters. This could indicate the need for further studies on
various techniques presented using solar water heaters. Based on the analysis of the selected
documents, the main conclusions are summarized below:
•
The most dominant phenomena in the solidification and melting processes are natu-
ral convection and conduction, so improving the thermal conductivity of PCM can
contribute to these two phenomena.
•
HTE enables better solidification and melting processes of PCM, in addition to increas-
ing the efficiency and performance of the heat exchanger. According to the literature,
passive methods are the most commonly used due to their simple application and
low cost.
•
Microencapsulation with a metallic coating has promising potential in various appli-
cations, such as hot water generation.
•
More simulations were conducted on the geometric variation technique, indicating
that, in some cases, manufacturing processes may be difficult to validate experimen-
tally, even if the results are promising.
•
When using various PCMs, the predominant parameters are PCM selection, and the
amount of PCM used. Poor selection of the quantity and type of PCM can lead to
unpromising results in energy storage.
•
Carbon-based nanoparticles could have a promising future in TES, but the use of recy-
clable or organic media cannot be ruled out, as it may positively impact
the environment.
•
According to the literature found on hot water generation, there is a lack of under-
standing of how these HTE techniques behave under user demand. This contributes to
a new research point, as it would provide a better estimate for real-world applications.
In particular, most HTE studies applied to hot water generation were conducted at the
laboratory scale, with constant flow rates.
•
No research was found comparing various HTE techniques in a single heat storage
model. Therefore, it is recommended that studies focused on these comparisons
be conducted to determine which technique yields better results in terms of system
efficiency improvement and solidification and melting processes.
•
According to the applied methodology, few documents were found on using active
methods in hot water generation. However, this article presents new techniques that
could help initiate new research through active methods or even generate new hybrid
methods by combining passive and active ones.
•
When comparing methods (active, passive, and hybrid) primarily used in hot water
generation applications, passive methods prevail due to their lower complexity. How-
ever, hybrid methods may provide a good option for a more efficient system and have
gained significant popularity recently. Currently, only hybrid methods combining
passive techniques have been found.
•
Nanofluids can enhance PCM’s properties or replace HTF in solar energy applications.
Nanofluids have made substantial advancements over the last decade due to their
ability to improve efficiency, thermal conductivity, and the geometry of solar collectors.
Energies 2024,17, 2350 27 of 35
•
Few studies were found discussing economic studies to assess the viability or prof-
itability of using different techniques. This could create a new research point, as it
would allow for comparing scientific results with creation and operation costs, thereby
determining which techniques are promising and cost-effective to apply in the field of
hot water generation.
Ultimately, this research opens up new opportunities for study and a deeper under-
standing of the techniques commonly used for HTE in HWGS.
Author Contributions: Conceptualization D.I.B., J.B.R., M.D.L.A.O.D.R., A.M.J.R. and I.H.; Method-
ology, and draft preparation, D.I.B.; review and editing, J.B.R., M.D.L.A.O.D.R. and A.M.J.R. All
authors have read and agreed to the published version of the manuscript.
Funding: This research was partially funded by Secretaría Nacional de Ciencia, Tecnología e In-
novación (SENACYT) in support of the Master of Science in Mechanical Engineering program,
VI Cohort.
Data Availability Statement: Not applicable.
Acknowledgments: The authors express their gratitude for the financial support provided by the
Master of Science Program in Mechanical Engineering at the Faculty of Mechanical Engineering
(https://fim.utp.ac.pa/ accessed on 11 February 2024), the Universidad Tecnológica de Panamá
(https://utp.ac.pa/ accessed on 11 February 2024), along with the Secretaría Nacional de Ciencia,
Tecnología e Innovación (SENACYT) and The National Research System (Sistema Nacional de
Investigación, SNI) of the Panamanian Government. Furthermore, special acknowledgment is given
to SENACYT for granting access to the Scientific Bibliography Access Platform (Plataforma de
Acceso a Bibliografía Científica, ABC), which facilitated the retrieval of information from the Scopus
database. Finally, we extend our gratitude to the biosolids laboratory at the Centro de Investigaciones
Hidráulicas e Hidrotécnicas (CIHH—https://codigestion.utp.ac.pa/ accessed on 10 May 2024), and
specifically acknowledge the invaluable assistance rendered by its researchers, Daniel Nieto, Marian
Ramírez, and Euclides Deago, during the course of this investigation.
Conflicts of Interest: The authors declare no conflicts of interest.
References
1.
Mahamude, A.S.F.; Kamarulzaman, M.K.; Harun, W.S.W.; Kadirgama, K.; Ramasamy, D.; Farhana, K.; Bakar, R.A.; Yusaf, T.;
Subramanion, S.; Yousif, B. A Comprehensive Review on Efficiency Enhancement of Solar Collectors Using Hybrid Nanofluids.
Energies 2022,15, 1391. [CrossRef]
2.
Quitiaquez, W.; Estupinán-Campos, J.; Nieto-Londoño, C.; Isaza-Roldán, C.A.; Quitiaquez, P.; Toapanta-Ramos, F. CFD Analysis
of Heat Transfer Enhancement in a Flat-Plate Solar Collector with Different Geometric Variations in the Superficial Section. Int. J.
Adv. Sci. Eng. Inf. Technol. 2021,11, 2039–2045. [CrossRef]
3.
Sikiru, S.; Oladosu, T.L.; Amosa, T.I.; Kolawole, S.Y.; Soleimani, H. Recent advances and impact of phase change materials on
solar energy: A comprehensive review. J. Energy Storage 2022,53, 105200. [CrossRef]
4.
Senthil, R.; Madurai Elavarasan, R.; Pugazhendhi, R.; Premkumar, M.; Vengadesan, E.; Navakrishnan, S.; Islam, M.R.; Natarajan,
S.K. A holistic review on the integration of heat pipes in solar thermal and photovoltaic systems. Sol. Energy 2021,227, 577–605.
[CrossRef]
5.
Harris Bernal, I.A.; James Rivas, A.M.; Ortega Del Rosario, M.D.L.A.; Saghir, M.Z. A Redesign Methodology to Improve the
Performance of a Thermal Energy Storage with Phase Change Materials: A Numerical Approach. Energies 2022,15, 960. [CrossRef]
6.
Suresh, C.; Saini, R.P. Review on solar thermal energy storage technologies and their geometrical configurations. Int. J. Energy Res.
2020,44, 4163–4195. [CrossRef]
7.
Prasad, D.M.R.; Senthilkumar, R.; Lakshmanarao, G.; Krishnan, S.; Naveen Prasad, B.S. A critical review on thermal energy
storage materials and systems for solar applications. AIMS Energy 2019,7, 507–526. [CrossRef]
8.
Yan, Z.; Yu, Z.J.; Yang, T.; Li, S.; Zhang, G. Impact of ultrasound on the melting process and heat transfer of phase change material.
Energy Procedia 2019,158, 5014–5019. [CrossRef]
9.
Arunachalam, S. Latent Heat Storage: Container Geometry, Enhancement Techniques, and Applications—A Review. J. Sol. Energy
Eng. 2019,141, 050801. [CrossRef]
10.
Dinker, A.; Agarwal, M.; Agarwal, G.D. Heat storage materials, geometry and applications: A review. J. Energy Inst. 2017,
90, 1–11.
[CrossRef]
11.
El Habib Amagour, M.; Rachek, A.; Bennajah, M.; Touhami, M.E. Numerical investigation and performance analysis of a compact
finned-tube heat exchanger uniformly filled with a phase change material for solar hot water production. In Proceedings of the
2019 International Conference of Computer Science and Renewable Energies (ICCSRE), Agadir, Morocco, 22–24 July 2019.
Energies 2024,17, 2350 28 of 35
12.
Cui, W.; Si, T.; Li, X.; Li, X.; Lu, L.; Ma, T.; Wang, Q. Heat transfer enhancement of phase change materials embedded with metal
foam for thermal energy storage: A review. Renew. Sustain. Energy Rev. 2022,169, 112912. [CrossRef]
13. Saxena, A.; Verma, P. Potential Techniques for Thermal Performance Enhancement for Solar Water Heaters; Department of Mechanical
Engineering, Moradabad Institute of Technology, Nova Science Publishers, Inc.: Moradabad, India, 2021.
14.
Frazzica, A.; Manzan, M.; Sapienza, A.; Freni, A.; Toniato, G.; Restuccia, G. Experimental testing of a hybrid sensible-latent heat
storage system for domestic hot water applications. Appl. Energy 2016,183, 1157–1167. [CrossRef]
15.
Nallusamy, N.; Sampath, S.; Velraj, R. Experimental investigation on a combined sensible and latent heat storage system integrated
with constant/varying (solar) heat sources. Renew. Energy 2007,32, 1206–1227. [CrossRef]
16.
Harris, I.; James Rivas, A.; Ortega Del Rosario, M.D.L.A.; Saghir, M.Z. Recent developments in phase change material-based solar
water heating systems: Insights on research trends and opportunities. Int. J. Thermofluids 2023,20, 100359. [CrossRef]
17.
Aggarwal, S.; Kumar, R.; Lee, D.; Kumar, S.; Singh, T. A comprehensive review of techniques for increasing the efficiency of
evacuated tube solar collectors. Heliyon 2023,9, e15185. [CrossRef] [PubMed]
18.
Gadhave, P.; Pathan, F.; Kore, S.; Prabhune, C. Comprehensive review of phase change material based latent heat thermal energy
storage system. Int. J. Ambient Energy 2022,43, 4181–4206. [CrossRef]
19.
Murali, G.; Mayilsamy, K. Effect of Latent Thermal Energy storage and inlet locations on enhancement of stratification in a solar
water heater under discharging mode. Appl. Therm. Eng. 2016,106, 354–360. [CrossRef]
20.
Zhang, N.; Yuan, Y.; Cao, X.; Du, Y.; Zhang, Z.; Gui, Y. Latent Heat Thermal Energy Storage Systems with Solid–Liquid Phase
Change Materials: A Review. Adv. Eng. Mater. 2018,20, 1700753. [CrossRef]
21.
Reddy, K.S.; Mudgal, V.; Mallick, T.K. Review of latent heat thermal energy storage for improved material stability and effective
load management. J. Energy Storage 2018,15, 205–227. [CrossRef]
22.
Sivasamy, P.; Devaraju, A.; Harikrishnan, S. Review on Heat Transfer Enhancement of Phase Change Materials (PCMs). Mater.
Today Proc. 2018,5, 14423–14431. [CrossRef]
23.
PCM Products Ltd. Types of Phase Change Materials. 2024. Available online: https://www.pcmproducts.net/Phase-Change-
Material-Solutions.htm (accessed on 4 May 2024).
24.
Huang, J.; Weng, M.; Yu, J.; Sun, L.; Zeng, H.; Liu, Y.; Zeng, W.; Min, Y.; Guo, Z. Advances and Applications of Phase Change
Materials (PCMs) and PCMs-based Technologies. ES Mater. Manuf. 2021,13, 23–39. [CrossRef]
25.
Youssef, W.; Ge, Y.T.; Tassou, S.A. CFD modelling development and experimental validation of a phase change material (PCM)
heat exchanger with spiral-wired tubes. Energy Convers. Manag. 2018,157, 498–510. [CrossRef]
26.
NematpourKeshteli, A.; Iasiello, M.; Langella, G.; Bianco, N. Thermal enhancement techniques for a lobed-double pipe PCM
thermal storage system. Appl. Therm. Eng. 2023,233, 121139. [CrossRef]
27.
Chow, T.-T.; Lyu, Y. Numerical analysis on the advantage of using PCM heat exchanger in liquid-flow window. Appl. Therm. Eng.
2017,125, 1218–1227. [CrossRef]
28.
Abokersh, M.H.; Osman, M.; El-Baz, O.; El-Morsi, M.; Sharaf, O. Review of the phase change material (PCM) usage for solar
domestic water heating systems (SDWHS). Int. J. Energy Res. 2018,42, 329–357. [CrossRef]
29.
Goel, V.; Saxena, A.; Kumar, M.; Thakur, A.; Sharma, A.; Bianco, V. Potential of phase change materials and their effective use in
solar thermal applications: A critical review. Appl. Therm. Eng. 2023,219, 119417. [CrossRef]
30.
Berrocal, D.; Blandon, J.; De Los Angeles, M.; Del Rosario, O.; Harris, I.; James, A. Phase Change Materials in Hot Water
Generation Systems: A Review. In Proceedings of the 2022 8th International Engineering, Sciences and Technology Conference
(IESTEC), Panama City, Panama, 19–21 October 2022; pp. 620–626. [CrossRef]
31.
Kumari, P.; Ghosh, D. A comparative numerical analysis of concentric and hairpin heat exchanger for efficient energy storage
using phase-change material. J. Therm. Anal. Calorim. 2023,148, 12211–12224. [CrossRef]
32.
Chen, X.; Yang, X. Heat transfer enhancement for U-pipe evacuated tube solar absorber by high-emissivity coating on metal fin.
J. Build. Eng. 2022,50, 104213. [CrossRef]
33.
Yang, M.; Moghimi, M.A.; Loillier, R.; Markides, C.N.; Kadivar, M. Design of a latent heat thermal energy storage system under
simultaneous charging and discharging for solar domestic hot water applications. Appl. Energy 2023,336, 120848. [CrossRef]
34.
Xiao, Y.; Huang, P.; Wei, G.; Cui, L.; Xu, C.; Du, X. State-of-the-art review on performance enhancement of photovoltaic/thermal
system integrated with phase change materials. J. Energy Storage 2022,56, 106073. [CrossRef]
35.
Muzhanje, A.T.; Hassan, M.A.; Ookawara, S.; Hassan, H. An overview of the preparation and characteristics of phase change
materials with nanomaterials. J. Energy Storage 2022,51, 104353. [CrossRef]
36.
Mohammed Sarhan, A.A.; Cornelis Metselaar, H.S.; Paria, S.; Baradaran, S.; Newaz, K.S.; Zalnehzad, E. Horizontal Heat Exchanger
for Thermal Energy Storage. Patent PCT/MY2015/050005, 27 August 2015.
37.
Ramarao, M.; Senthil Kumar, S.; Jayakrishna, S.; SUBBIAH, R.; Pushpanathan, D.P.; Babu, M.N.; Gopal, M.; Raju, M.M.;
Thillaivanan, D.A.; Srikanth, G.B.; et al. Solar Thermal and PV-T Systems for Domestic Applications. Patent 202141010836,
26 March 2021.
38. Mier Ruiz, J.M. Sistema de Calentamiento de Agua Por Energia Solar. Patent 200601705, 27 October 2009.
39.
Narayanan, S.S.; Kardam, A.; Kumar, V.; Verma, A.; Bhardwaj, N.; Madhwal, D.; Shukla, P.; Kumar, A.; Jain, V.K. Design
and Fabrication of Instant Solar Thermal Water Heating System Based on Phase Change Material-Nanocomposite. Patent
201611024244, 19 January 2018.
Energies 2024,17, 2350 29 of 35
40.
Iyengar, V.N.; Badkoobeh, O. Thermally Regulated Modular Energy Storage Device and Methods. Patent PCT/US2018/025886,
11 October 2018.
41.
Jamar, A.; Majid, Z.A.A.; Azmi, W.H.; Norhafana, M.; Razak, A.A. A review of water heating system for solar energy applications.
Int. Commun. Heat Mass Transf. 2016,76, 178–187. [CrossRef]
42.
Kabbara, M.; Groulx, D.; Joseph, A. Experimental Study of a Latent Heat Storage Unit with a Helical Coil Heat Exchanger. 2014.
Available online: https://www.researchgate.net/publication/263423590 (accessed on 28 January 2024).
43.
Shank, K.; Bernat, J.; Regal, E.; Leise, J.; Ji, X.; Tiari, S. Experimental Study of Varying Heat Transfer Fluid Parameters within a
Latent Heat Thermal Energy Storage System Enhanced by Fins. Sustainability 2022,14, 8920. [CrossRef]
44.
Liu, W.; Bie, Y.; Xu, T.; Cichon, A.; Królczyk, G.; Li, Z. Heat transfer enhancement of latent heat thermal energy storage in solar
heating system: A state-of-the-art review. J. Energy Storage 2022,46, 103727. [CrossRef]
45.
Qiu, L.; Ouyang, Y.; Feng, Y.; Zhang, X. Review on micro/nano phase change materials for solar thermal applications. Renew.
Energy 2019,140, 513–538. [CrossRef]
46.
Shank, K.; Tiari, S. A Review on Active Heat Transfer Enhancement Techniques within Latent Heat Thermal Energy Storage
Systems. Energies 2023,16, 4165. [CrossRef]
47.
Jacob, R.; Saman, W.; Belusko, M.; Bruno, F. Techno-Economic Analysis of Phase Change Material Thermal Energy Storage
Systems in High Temperature Concentrated Solar Power Plants. In Proceedings of the Asia-Pacific Solar Research Conference,
Sydney, Australia, 8–10 December 2014. Available online: http://apvi.org.au/solar-research-conference/wp-content/uploads/
2015/04/6-R-Jacob_peer_reviewed.pdf (accessed on 20 January 2024).
48.
Panchal, J.M.; Modi, K.V.; Patel, V.J. Development in multiple-phase change materials cascaded low-grade thermal energy storage
applications: A review. Clean. Eng. Technol. 2022,8, 100465. [CrossRef]
49.
Al-Abidi, A.A.; Mat, S.; Sopian, K.; Sulaiman, M.Y.; Mohammad, A.T. Internal and external fin heat transfer enhancement
technique for latent heat thermal energy storage in triplex tube heat exchangers. Appl. Therm. Eng. 2013,53, 147–156. [CrossRef]
50.
He, N.; Feng, G.; Wang, T. Research progress on solar energy storage water tanks based on phase-change materials. Gongcheng
Kexue Xuebao/Chin. J. Eng. 2023,45, 1795–1806. [CrossRef]
51. Joybari, M.M.; Seddegh, S.; Wang, X.; Haghighat, F. Experimental investigation of multiple tube heat transfer enhancement in a
vertical cylindrical latent heat thermal energy storage system. Renew. Energy 2019,140, 234–244. [CrossRef]
52.
Venkateswarlu, K.; Varma, K.P.V.K.; Nutakki, U.K. Synthesis, characterization and application of mono-, hybrid and ternary
nanofluids in hybrid photovoltaic thermal (PV/T) solar systems—A review. J. Braz. Soc. Mech. Sci. Eng. 2022,44, 550. [CrossRef]
53.
Sharma, M.K. Alternative designs and technological advancements of phase change material integrated photovoltaics: A
state-of-the-art review. J. Energy Storage 2022,48, 104020. [CrossRef]
54.
Maridurai, T.; Harrish Ahamed, K.; Loganathan, K. Performance enhancement with different geometry of thermal energy storage
systems. Int. J. Mech. Prod. Eng. Res. Dev. 2018,8, 1210–1213. Available online: https://www.scopus.com/record/display.uri?
eid=2-s2.0-85063215440&origin=inward&txGid=6ad7e3e4efc0468132df399a6ef057b9 (accessed on 6 February 2024).
55.
Nedjem, K.; Teggar, M.; Ismail, K.A.R.; Nehari, D. Numerical investigation of charging and discharging processes of a shell and
tube nano-enhanced latent thermal storage unit. J. Therm. Sci. Eng. Appl. 2020,12, 021021. [CrossRef]
56.
Kumar, A.; Kumar, A. Heat transfer analysis in thermal energy storage—A comprehensive review-based latent heat storage
system. Energy Storage 2023,5, est2.434. [CrossRef]
57.
Sundaramahalingam, A.; Jegadheeswaran, S.; Ponmurugan, M.; Sasikumar, C. Review on Thermal Energy Storage with Phase
Change Materials and Its Applications. In Advances in Materials Research: Select Proceedings of ICAMR 2019; Springer: Singapore,
2021; Volume 5, pp. 543–554.
58.
Kumar, G.S.; Nagarajan, D.; Chidambaram, L.A.; Kumaresan, V.; Ding, Y.; Velraj, R. Role of PCM addition on stratification
behaviour in a thermal storage tank—An experimental study. Energy 2016,115, 1168–1178. [CrossRef]
59.
Langarón Cabello, J.M.; Pérez Masía, R.; López Rubio, A. Procedimiento de Encapsulación de PCMs. Patent PCT/ES2012/070456,
27 December 2012.
60.
Hashim, D.P. Three-Dimensional Carbon Nanotube Sponge Materials as Absorbers of Phase Change Materials.
Patent 20220234895
,
28 July 2022.
61. Kirschner, T. System and Method for Producing Domestic Hot Water. Patent 20240110708, 4 April 2024.
62.
Singh, D.; Cingarapu, S.; Moravek, M.; Timofeeva, E.V. Nanoparticles for Heat Transfer and Thermal Energy Storage.
Patent 20150307763, 29 October 2015.
63.
United Nations Population Division Countries in the World by Population (2024). Worldometer, 2023. Available online:
https://www.worldometers.info/world-population/population-by-country/ (accessed on 2 May 2024).
64.
Yu, Z.; Wang, J.; Yan, Z.; Tuo, X.; Li, S.; Zhagn, G. Study on Improvement and Melting Performance of Phase Change Material
Encapsulated Structure in Domestic Hot Water Tank. Hunan Daxue Xuebao/J. Hunan Univ. Nat. Sci. 2021,48, 215–222. [CrossRef]
65.
Zhu, M.; Wang, Z.; Qi, H.; Sun, X.; Zhou, X. Experimental research and numerical simulation on the enhanced heat transfer
mechanism of foamed copper to paraffin. Gongneng Cailiao/J. Funct. Mater. 2021,52, 11195–11201. [CrossRef]
66.
Zhang, P.; Xiao, X.; Ma, Z.W. A review of the composite phase change materials: Fabrication, characterization, mathematical
modeling and application to performance enhancement. Appl. Energy 2016,165, 472–510. [CrossRef]
67.
Lin, Y.; Jia, Y.; Alva, G.; Fang, G. Review on thermal conductivity enhancement, thermal properties and applications of phase
change materials in thermal energy storage. Renew. Sustain. Energy Rev. 2018,82, 2730–2742. [CrossRef]
Energies 2024,17, 2350 30 of 35
68.
Agyenim, F.; Hewitt, N.; Eames, P.; Smyth, M. A review of materials, heat transfer and phase change problem formulation for
latent heat thermal energy storage systems (LHTESS). Renew. Sustain. Energy Rev. 2010,14, 615–628. [CrossRef]
69.
Habibishandiz, M.; Saghir, M.Z. A critical review of heat transfer enhancement methods in the presence of porous media,
nanofluids, and microorganisms. Therm. Sci. Eng. Prog. 2022,30, 101267. [CrossRef]
70.
Gadhave, P.; Prabhune, C.; Pathan, F. Selection of phase change material for domestic water heating using multi criteria decision
approach. Aust. J. Mech. Eng. 2020,21, 295–315. [CrossRef]
71.
Zhang, S.; Mancin, S.; Pu, L. A review and prospective of fin design to improve heat transfer performance of latent thermal
energy storage. J. Energy Storage 2023,62, 106825. [CrossRef]
72.
Khademi, A.; Shank, K.; Mehrjardi, S.A.A.; Tiari, S.; Sorrentino, G.; Said, Z.; Chamkha, A.J.; Ushak, S. A brief review on different
hybrid methods of enhancement within latent heat storage systems. J. Energy Storage 2022,54, 105362. [CrossRef]
73.
Kamkari, B.; Groulx, D. Experimental investigation of melting behaviour of phase change material in finned rectangular enclosures
under different inclination angles. Exp. Therm. Fluid Sci. 2018,97, 94–108. [CrossRef]
74.
Merlin, K.; Delaunay, D.; Soto, J.; Traonvouez, L. Heat transfer enhancement in latent heat thermal storage systems: Comparative
study of different solutions and thermal contact investigation between the exchanger and the PCM. Appl. Energy 2016,
166, 107–116
.
[CrossRef]
75.
Aramesh, M.; Shabani, B. Experimental evaluation of a self storage integrated evacuated tube solar thermal collector. J. Energy
Storage 2023,62, 106920. [CrossRef]
76.
Aramesh, M.; Shabani, B. Metal foams application to enhance the thermal performance of phase change materials: A review of
experimental studies to understand the mechanisms. J. Energy Storage 2022,50, 104650. [CrossRef]
77.
Shin, D.H.; Park, J.; Choi, S.H.; Ko, H.S.; Karng, S.W.; Shin, Y. A new type of heat storage system using the motion of phase
change materials in an elliptical-shaped capsule. Energy Convers. Manag. 2019,182, 508–519. [CrossRef]
78.
Asgari, M.; Javidan, M.; Nozari, M.; Asgari, A.; Ganji, D.D. Simulation of solidification process of phase change materials in a
heat exchanger using branch-shaped fins. Case Stud. Therm. Eng. 2021,25, 100835. [CrossRef]
79.
El-Sebaey, M.S.; El-Din, S.S.; El-Kholy, M.K. Heat transfer and fluid flow performance of an internally longitudinal finned tube:
Numerical study and experimental validation. Int. J. Therm. Sci. 2024,201, 109025. [CrossRef]
80.
Joybari, M.M.; Haghighat, F.; Seddegh, S.; Al-Abidi, A.A. Heat transfer enhancement of phase change materials by fins under
simultaneous charging and discharging. Energy Convers. Manag. 2017,152, 136–156. [CrossRef]
81.
Das, P.; Kar, S.P.; Sarangi, R.K. Review on thermal performance of heat exchanger using phase change material. Int. J. Energy Res.
2022,46, 16208–16240. [CrossRef]
82.
Acır, A.; Emin Canlı, M. Investigation of fin application effects on melting time in a latent thermal energy storage system with
phase change material (PCM). Appl. Therm. Eng. 2018,144, 1071–1080. [CrossRef]
83.
Hosseini, M.J.; Ranjbar, A.A.; Rahimi, M.; Bahrampoury, R. Experimental and numerical evaluation of longitudinally finned
latent heat thermal storage systems. Energy Build. 2015,99, 263–272. [CrossRef]
84.
Kalbasi, R.; Salimpour, M.R. Constructal design of horizontal fins to improve the performance of phase change material rectangular
enclosures. Appl. Therm. Eng. 2015,91, 234–244. [CrossRef]
85.
Khan, Z.; Khan, Z.; Ghafoor, A. A review of performance enhancement of PCM based latent heat storage system within the
context of materials, thermal stability and compatibility. Energy Convers. Manag. 2016,115, 132–158. [CrossRef]
86.
Tavakoli, A.; Farzaneh-Gord, M.; Ebrahimi-Moghadam, A. Using internal sinusoidal fins and phase change material for
performance enhancement of thermal energy storage systems: Heat transfer and entropy generation analyses. Renew. Energy
2023,205, 222–237. [CrossRef]
87.
Mao, Q.; Li, Y.; Li, G.; Badiei, A. Study on the influence of tank structure and fin configuration on heat transfer performance of
phase change thermal storage system. Energy 2021,235, 121382. [CrossRef]
88.
Kabbara, M.; Groulx, D.; Joseph, A. Experimental investigations of a latent heat energy storage unit using finned tubes. Appl.
Therm. Eng. 2016,101, 601–611. [CrossRef]
89.
Hassan, A.K.; Abdulateef, J.; Mahdi, M.S.; Hasan, A.F. Experimental evaluation of thermal performance of two different finned
latent heat storage systems. Case Stud. Therm. Eng. 2020,21, 100675. [CrossRef]
90.
Hosseini, M.M.; Rahimi, A.B. Improving heat transfer in a triplex tube heat exchanger containing phase-change materials by
modifications of length and position of fins. Sci. Iran. 2020,27, 239–251. [CrossRef]
91.
Amagour, M.E.H.; Bennajah, M.; Rachek, A. Numerical investigation and experimental validation of the thermal performance
enhancement of a compact finned-tube heat exchanger for efficient latent heat thermal energy storage. J. Clean. Prod. 2021,
280, 124238. [CrossRef]
92.
Amagour, M.E.H.; Rachek, A.; Bennajah, M.; Ebn Touhami, M. Experimental investigation and comparative performance analysis
of a compact finned-tube heat exchanger uniformly filled with a phase change material for thermal energy storage. Energy
Convers. Manag. 2018,165, 137–151. [CrossRef]
93.
Mat, S.; Al-Abidi, A.A.; Sopian, K.; Sulaiman, M.Y.; Mohammad, A.T. Enhance heat transfer for PCM melting in triplex tube with
internal–external fins. Energy Convers. Manag. 2013,74, 223–236. [CrossRef]
94.
Li, J.; Abdulghani, Z.R.; Alghamdi, M.N.; Sharma, K.; Niyas, H.; Moria, H.; Arsalanloo, A. Effect of twisted fins on the melting
performance of PCM in a latent heat thermal energy storage system in vertical and horizontal orientations: Energy and exergy
analysis. Appl. Therm. Eng. 2023,219, 119489. [CrossRef]
Energies 2024,17, 2350 31 of 35
95.
Rogowski, M.; Andrzejczyk, R. Recent advances of selected passive heat transfer intensification methods for phase change
material-based latent heat energy storage units: A review. Int. Commun. Heat Mass Transf. 2023,144, 106795. [CrossRef]
96.
Zaidan, M.J.; Alhamdo, M.H. Effect of perforated and smooth fins on thermal performance of a latent heat energy system. J. Eng.
Sustain. Dev. 2019,23, 109–128. [CrossRef]
97.
Rahimi, M.; Ranjbar, A.A.; Ganji, D.D.; Sedighi, K.; Hosseini, M.J.; Bahrampoury, R. Analysis of geometrical and operational
parameters of PCM in a fin and tube heat exchanger. Int. Commun. Heat Mass Transf. 2014,53, 109–115. [CrossRef]
98.
Patel, J.R.; Rathod, M.K. Thermal performance enhancement of melting and solidification process of phase-change material in
triplex tube heat exchanger using longitudinal fins. Heat Transf. 2019,48, 483–501. [CrossRef]
99.
Yang, X.; Wang, X.; Liu, Z.; Luo, X.; Yan, J. Effect of fin number on the melting phase change in a horizontal finned shell-and-tube
thermal energy storage unit. Sol. Energy Mater. Sol. Cells 2022,236, 111527. [CrossRef]
100.
Kirincic, M.; Trp, A.; Lenic, K. Numerical evaluation of the latent heat thermal energy storage performance enhancement by
installing longitudinal fins. J. Energy Storage 2021,42, 103085. [CrossRef]
101.
Irbai’, A.S.I.; Najjar, Y.S.H. Enhancement of the melting process in the thermal energy storage system by using novel geometry.
Numer. Heat Transf. Part A Appl. 2019,76, 1006–1022. [CrossRef]
102.
Rana, S.; Zunaid, M.; Kumar, R. Enhancement of thermal energy storage in a phase change material heat exchanger having
elliptical and circular tubes with & without fins. J. Energy Storage 2022,56, 105856. [CrossRef]
103.
Liu, C.; Groulx, D. Experimental study of the phase change heat transfer inside a horizontal cylindrical latent heat energy storage
system. Int. J. Therm. Sci. 2014,82, 100–110. [CrossRef]
104.
Sekhar, Y.R.; Sharma, K.V.; Karupparaj, R.T.; Chiranjeevi, C. Heat transfer enhancement with Al
2
O
3
nanofluids and twisted tapes
in a pipe for solar thermal applications. Procedia Eng. 2013,64, 1474–1484. [CrossRef]
105.
Castle, A. Twisted Tape Turbulators. Fuel Efficiency. 2024. Available online: https://www.fuelefficiencyllc.com/twisted-tape-
turbulators/ (accessed on 6 February 2024).
106.
Sakhaei, S.A.; Valipour, M.S. Performance enhancement analysis of The flat plate collectors: A comprehensive review. Renew.
Sustain. Energy Rev. 2019,102, 186–204. [CrossRef]
107.
Sadhishkumar, S.; Balusamy, T. Performance improvement in solar water heating systems—A review. Renew. Sustain. Energy Rev.
2014,37, 191–198. [CrossRef]
108.
Zaboli, M.; Saedodin, S.; Ajarostaghi, S.S.M.; Karimi, N. Recent Progress on Flat Plate Solar Collectors Equipped with Nanofluid and
Turbulator: State of the Art; Springer: Berlin/Heidelberg, Germany, 2023; Volume 30.
109.
Khargotra, R.; Alam, T.; Thu, K.; András, K.; Siddiqui, T.U.; Singh, T. Influence of heat enhancement technique on the thermal
performance of solar water heater for sustainable built environment. Start-of-the-art review. Sustain. Energy Technol. Assess. 2023,
57, 103293. [CrossRef]
110.
Jaisankar, S.; Radhakrishnan, T.K.; Sheeba, K.N. Experimental studies on heat transfer and friction factor characteristics of forced
circulation solar water heater system fitted with helical twisted tapes. Sol. Energy 2009,83, 1943–1952. [CrossRef]
111.
Hobbi, A.; Siddiqui, K. Experimental study on the effect of heat transfer enhancement devices in flat-plate solar collectors. Int. J.
Heat Mass Transf. 2009,52, 4650–4658. [CrossRef]
112.
Hamidia, E.; Ganesan, P.B.; Sharma, R.K.; Yong, K.W. Computational study of heat transfer enhancement using porous foams
with phase change materials: A comparative review. Renew. Sustain. Energy Rev. 2023,176, 113196. [CrossRef]
113.
Gaedtke, M.; Abishek, S.; Mead-Hunter, R.; King, A.J.C.; Mullins, B.J.; Nirschl, H.; Krause, M.J. Total enthalpy-based lattice
Boltzmann simulations of melting in paraffin/metal foam composite phase change materials. Int. J. Heat Mass Transf. 2020,
155, 119870. [CrossRef]
114.
Majdi, H.S.; Abed, A.M.; Habeeb, L.J. Performance evaluation of a solar water heater integrated with built-In thermal energy
storage via porous media. Front. Heat Mass Transf. 2021,17, 1–10. [CrossRef]
115.
Zhao, C.Y.; Lu, W.; Tian, Y. Heat transfer enhancement for thermal energy storage using metal foams embedded within phase
change materials (PCMs). Sol. Energy 2010,84, 1402–1412. [CrossRef]
116.
Tian, Y.; Zhao, C.Y. A numerical investigation of heat transfer in phase change materials (PCMs) embedded in porous metals.
Energy 2011,36, 5539–5546. [CrossRef]
117.
Zhang, S.; Pu, L.; Mancin, S.; Ma, Z.; Xu, L. Experimental study on heat transfer characteristics of metal foam/paraffin composite
PCMs in large cavities: Effects of material types and heating configurations. Appl. Energy 2022,325, 119790. [CrossRef]
118.
Xiao, X.; Zhang, P.; Li, M. Effective thermal conductivity of open-cell metal foams impregnated with pure paraffin for latent heat
storage. Int. J. Therm. Sci. 2014,81, 94–105. [CrossRef]
119.
Zhu, M.; Wang, Z.; Sun, X.; Zhou, X. Experimental research on effect of copper metal foam proportion on paraffin wax melting
and heat transfer mechanism under high cell density. Huagong Jinzhan/Chem. Ind. Eng. Prog. 2022,41, 3203–3211. [CrossRef]
120.
Alam, M.T.; Raj, A.; Singh, L.K.; Gupta, A.K. Configurational assessment of solidification performance in a triplex-tube heat
exchanger filled with composite phase change material. Appl. Therm. Eng. 2023,230, 120814. [CrossRef]
121.
Wang, Z.; Zhang, H.; Dou, B.; Zhang, G.; Wu, W.; Zhou, X. Effect of copper metal foam proportion on heat transfer enhancement
in the melting process of phase change materials. Appl. Therm. Eng. 2022,201, 117778. [CrossRef]
122.
Yang, X.; Wei, P.; Cui, X.; Jin, L.; He, Y.-L. Thermal response of annuli filled with metal foam for thermal energy storage: An
experimental study. Appl. Energy 2019,250, 1457–1467. [CrossRef]
Energies 2024,17, 2350 32 of 35
123.
Shankar Baruah, J.; Athawale, V.; Prasenjit, R.; Bhattacharya, A. Melting and energy storage characteristics of macro-encapsulated
PCM-metal foam system. Int. J. Heat Mass Transf. 2022,182, 121993. [CrossRef]
124.
Ghalambaz, M.; Chamkha, A.J.; Wen, D. Natural convective flow and heat transfer of Nano-Encapsulated Phase Change Materials
(NEPCMs) in a cavity. Int. J. Heat Mass Transf. 2019,138, 738–749. [CrossRef]
125.
Luo, K.; Ye, W.; Wang, Y.; Zeng, Z.; Liu, J.; Fei, H. Research progress of phase change energy storage in solar domestic hot water
system. Taiyangneng Xuebao/Acta Energiae Solaris Sin. 2022,43, 220–229. [CrossRef]
126.
Salunkhe, P.B.; Shembekar, P.S. A review on effect of phase change material encapsulation on the thermal performance of a
system. Renew. Sustain. Energy Rev. 2012,16, 5603–5616. [CrossRef]
127.
Navarro, L.; Barreneche, C.; Castell, A.; Redpath, D.A.G.; Griffiths, P.W.; Cabeza, L.F. High density polyethylene spheres with
PCM for domestic hot water applications: Water tank and laboratory scale study. J. Energy Storage 2017,13, 262–267. [CrossRef]
128.
Xu, B.; Chen, C.; Zhou, J.; Ni, Z.; Ma, X. Preparation of novel microencapsulated phase change material with Cu-Cu
2
O/CNTs as
the shell and their dispersed slurry for direct absorption solar collectors. Sol. Energy Mater. Sol. Cells 2019,200, 109980. [CrossRef]
129.
Xu, L.; Pu, L.; Zhang, S.; Ma, Z. Thermo-fluidic performance of microencapsulated phase change material slurry in thermal
energy storage. J. Energy Storage 2021,43, 103247. [CrossRef]
130.
Li, W.Q.; Guo, S.J.; Tan, L.; Liu, L.L.; Ao, W. Heat transfer enhancement of nano-encapsulated phase change material (NEPCM)
using metal foam for thermal energy storage. Int. J. Heat Mass Transf. 2021,166, 120737. [CrossRef]
131.
Ibáñez, M.; Cabeza, L.F.; Solé, C.; Roca, J.; Nogués, M. Modelization of a water tank including a PCM module. Appl. Therm. Eng.
2006,26, 1328–1333. [CrossRef]
132.
Mehling, H.; Cabeza, L.F.; Hippeli, S.; Hiebler, S. PCM-module to improve hot water heat stores with stratification. Renew. Energy
2003,28, 699–711. [CrossRef]
133.
Sun, V.; Asanakham, A.; Deethayat, T.; Kiatsiriroat, T. Performance analysis on combined heat and power of photovoltaic-thermal
module integrated with phase change material-water storage. J. Energy Storage 2022,47, 103614. [CrossRef]
134.
Punniakodi, B.M.S.; Senthil, R. A review on container geometry and orientations of phase change materials for solar thermal
systems. J. Energy Storage 2021,36, 102452. [CrossRef]
135.
Yan, Z.; Zhu, Y.; Liu, L.; Yu, Z.J.; Li, S.; Zhang, G. Performance enhancement of cylindrical latent heat storage units in hot water
tanks via wavy design. Renew. Energy 2023,218, 119282. [CrossRef]
136.
Quitiaquez, W.; Estupiñán-Campos, J.; Nieto-Londoño, C.; Quitiaquez, P. CFD Analysis of Heat Transfer Enhancement in a
Flat-Plate Solar Collector/Evaporator with Different Geometric Variations in the Cross Section. Energies 2023,16, 5755. [CrossRef]
137.
Wong, T.L.; Vallés, C.; Nasser, A.; Abeykoon, C. A critical experimental evaluation of hexagonal boron nitride, graphene oxide
and graphite as thermally conductive fillers in organic PCMs. J. Energy Storage 2023,72, 108523. [CrossRef]
138.
Hasib, A.M.M.G.; Rayegan, R.; Tao, Y.X. Investigation of using dispersed particle and branching heat exchanger in medium
temperature thermal energy storage system to achieve maximum utilization of solar power. In Proceedings of the ASME
International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), San Diego, CA, USA, 15–21 November
2013; American Society of Mechanical Engineers (ASME), University of North Texas: Denton, TX, USA, 2013; Volume 8B.
139.
Sett, K.Y.; Mon, M.S. The effect of expanded graphite on the charging time of stearic acid phase change material in a hot water
tank. ASEAN Eng. J. 2021,11, 14–24. [CrossRef]
140.
Li, C.; Zhang, B.; Xie, B.; Zhao, X.; Chen, J.; Chen, Z.; Long, Y. Stearic acid/expanded graphite as a composite phase change
thermal energy storage material for tankless solar water heater. Sustain. Cities Soc. 2019,44, 458–464. [CrossRef]
141.
D’Oliveira, E.J.; Pereira, S.C.C.; Groulx, D.; Azimov, U. Thermophysical properties of Nano-enhanced phase change materials for
domestic heating applications. J. Energy Storage 2022,46, 103794. [CrossRef]
142.
Hu, Y.; Yang, J.; Tian, J.; Jia, L.; Yu, J.-S. Green and size-controllable synthesis of photoluminescent carbon nanoparticles from
waste plastic bags. RSC Adv. 2014,4, 47169–47176. [CrossRef]
143.
Hassan, T.A.; Rangari, V.K.; Jeelani, S. Mechanical and thermal properties of bio-based CaCO
3
/soybean-based hybrid unsaturated
polyester nanocomposites. J. Appl. Polym. Sci. 2013,130, 1442–1452. [CrossRef]
144.
Biswas, A.; Patra, A.K.; Sarkar, S.; Das, D.; Chattopadhyay, D.; De, S. Synthesis of highly magnetic iron oxide nanomaterials from
waste iron by one-step approach. Colloids Surfaces A Physicochem. Eng. Asp. 2020,589, 124420. [CrossRef]
145.
Rajarao, R.; Ferreira, R.; Fahandej Sadi, S.H.; Khanna, R.; Sahajwalla, V. Synthesis of silicon carbide nanoparticles by using
electronic waste as a carbon source. Mater. Lett. 2014,120, 65–68. [CrossRef]
146.
Rangari, V.K.; Apalangya, V.; Biswas, M.; Jeelani, S. Preparation and microscopic characterization of biobased nanoparticles from
natural waste materials. Microsc. Microanal. 2017,23, 1938–1939. [CrossRef]
147.
Mehryan, S.A.M.; Ghalambaz, M.; Sasani Gargari, L.; Hajjar, A.; Sheremet, M. Natural convection flow of a suspension containing
nano-encapsulated phase change particles in an eccentric annulus. J. Energy Storage 2020,28, 101236. [CrossRef]
148.
Agrawal, R.; Singh, K.D.P.; Paswan, M.K. Review on Enhancement of Thermal Conductivity of Phase Change Materials with
Nano-Particle in Engineering Applications. Mater. Today Proc. 2020,22, 1617–1627. [CrossRef]
149.
Teamah, H.M.; Teamah, M. Integration of phase change material in flat plate solar water collector: A state of the art, opportunities,
and challenges. J. Energy Storage 2022,54, 105357. [CrossRef]
150.
Cabeza, L.F.; Ibáñez, M.; Solé, C.; Roca, J.; Nogués, M. Experimentation with a water tank including a PCM module. Sol. Energy
Mater. Sol. Cells 2006,90, 1273–1282. [CrossRef]
Energies 2024,17, 2350 33 of 35
151.
Xie, B.; Li, C.; Zhang, B.; Yang, L.; Xiao, G.; Chen, J. Evaluation of stearic acid/coconut shell charcoal composite phase change
thermal energy storage materials for tankless solar water heater. Energy Built Environ. 2020,1, 187–198. [CrossRef]
152.
Haillot, D.; Nepveu, F.; Goetz, V.; Py, X.; Benabdelkarim, M. High performance storage composite for the enhancement of solar
domestic hot water systems: Part 2: Numerical system analysis. Sol. Energy 2012,86, 64–77. [CrossRef]
153.
Sadiq, I.E.; Aljabai, S.; Karamallah, A.A. Effect of Al
2
O
3
/CuO Hybrid Nanoparticles Dispersion on Melting Process of PCM in a
Triplex Tube Heat Storage. FME Trans. 2023,51, 606–626. [CrossRef]
154.
Mandal, S.K.; Singh, P.K.; Kumar, S.; Mishra, S.K. Parametric investigation of CuO-doped charged nanofluid in solar water heater.
Int. J. Environ. Sci. Technol. 2021,18, 2855–2864. [CrossRef]
155.
Gorzin, M.; Hosseini, M.J.; Rahimi, M.; Bahrampoury, R. Nano-enhancement of phase change material in a shell and multi-PCM-
tube heat exchanger. J. Energy Storage 2019,22, 88–97. [CrossRef]
156.
Al-Kayiem, H.H.; Lin, S.C. Performance evaluation of a solar water heater integrated with a PCM nanocomposite TES at various
inclinations. Sol. Energy 2014,109, 82–92. [CrossRef]
157.
Rao, Z.; Wen, Y.; Liu, C. Enhancement of heat transfer of microcapsulated particles using copper particles and copper foam.
Particuology 2018,41, 85–93. [CrossRef]
158.
Christopher, S.; Parham, K.; Mosaffa, A.H.; Farid, M.M.; Ma, Z.; Thakur, A.K.; Xu, H.; Saidur, R. A critical review on phase change
material energy storage systems with cascaded configurations. J. Clean. Prod. 2021,283, 124653. [CrossRef]
159.
Gong, Z.-X.; Mujumdar, A.S. A New Solar Receiver Thermal Store for Space-Based Activities Using Multiple Composite
Phase-Change Materials. J. Sol. Energy Eng. 1995,117, 215–220. [CrossRef]
160.
Narasimhan, N.L. Assessment of latent heat thermal storage systems operating with multiple phase change materials. J. Energy
Storage 2019,23, 442–455. [CrossRef]
161. Ali, H.M.; Rehman, T.-U.; Arıcı, M.; Said, Z.; Durakovi´c, B.; Mohammed, H.I.; Kumar, R.; Rathod, M.K.; Buyukdagli, O.; Teggar,
M. Advances in thermal energy storage: Fundamentals and applications. Prog. Energy Combust. Sci. 2024,100, 101109. [CrossRef]
162.
Farid, M.M.; Kim, Y.; Kansawa, A. Thermal Performance of a Heat Storage Module Using PCM’s with Different Melting
Temperature: Experimental. J. Energy Resour. Technol. 1990,112, 125–131. [CrossRef]
163.
Kurnia, J.C.; Sasmito, A.P.; Jangam, S.V.; Mujumdar, A.S. Improved design for heat transfer performance of a novel phase change
material (PCM) thermal energy storage (TES). Appl. Therm. Eng. 2013,50, 896–907. [CrossRef]
164.
Aldoss, T.K.; Rahman, M.M. Comparison between the single-PCM and multi-PCM thermal energy storage design. Energy Convers.
Manag. 2014,83, 79–87. [CrossRef]
165.
Wang, J.; Ouyang, Y.; Chen, G. Experimental study on charging processes of a cylindrical heat storage capsule employing
multiple-phase-change materials. Int. J. Energy Res. 2001,25, 439–447. [CrossRef]
166.
Mazman, M.; Cabeza, L.F.; Mehling, H.; Nogues, M.; Evliya, H.; Paksoy, H.Ö. Utilization of phase change materials in solar
domestic hot water systems. Renew. Energy 2009,34, 1639–1643. [CrossRef]
167.
Lim, J.S.; Bejan, A.; Kim, J.H. Thermodynamic Optimization of Phase-Change Energy Storage Using Two or More Materials.
J. Energy Resour. Technol. 1992,114, 84–90. [CrossRef]
168.
Khor, J.O.; Sze, J.Y.; Li, Y.; Romagnoli, A. Overcharging of a cascaded packed bed thermal energy storage: Effects and solutions.
Renew. Sustain. Energy Rev. 2020,117, 109421. [CrossRef]
169.
Pu, L.; Zhang, S.; Xu, L.; Ma, Z.; Wang, X. Numerical study on the performance of shell-and-tube thermal energy storage using
multiple PCMs and gradient copper foam. Renew. Energy 2021,174, 573–589. [CrossRef]
170.
Rahimi, M.; Ardahaie, S.S.; Hosseini, M.J.; Gorzin, M. Energy and exergy analysis of an experimentally examined latent heat
thermal energy storage system. Renew. Energy 2020,147, 1845–1860. [CrossRef]
171.
Kasaeian, A.; Eshghi, A.T.; Sameti, M. A review on the applications of nanofluids in solar energy systems. Renew. Sustain. Energy
Rev. 2015,43, 584–598. [CrossRef]
172.
Kunwer, R.; Donga, R.K.; Kumar, R.; Singh, H. Thermal Characterization of Flat Plate Solar Collector Using Titanium Dioxide
Nanofluid. Process Integr. Optim. Sustain. 2023,7, 1333–1343. [CrossRef]
173.
Muhammad, M.J.; Muhammad, I.A.; Sidik, N.A.C.; Yazid, M.N.A.W.M.; Mamat, R.; Najafi, G. The use of nanofluids for enhancing
the thermal performance of stationary solar collectors: A review. Renew. Sustain. Energy Rev. 2016,63, 226–236. [CrossRef]
174.
Said, Z.; Hachicha, A.A.; Aberoumand, S.; Yousef, B.A.A.; Sayed, E.T.; Bellos, E. Recent advances on nanofluids for low to
medium temperature solar collectors: Energy, exergy, economic analysis and environmental impact. Prog. Energy Combust. Sci.
2021,84, 100898. [CrossRef]
175.
Kazaz, O.; Karimi, N.; Kumar, S.; Falcone, G.; Paul, M.C. Heat transfer characteristics of fluids containing paraffin core-metallic
shell nanoencapsulated phase change materials for advanced thermal energy conversion and storage applications. J. Mol. Liq.
2023,385, 122385. [CrossRef]
176.
Ali, N.; Bahman, A.M.; Aljuwayhel, N.F.; Ebrahim, S.A.; Mukherjee, S.; Alsayegh, A. Carbon-based nanofluids and their advances
towards heat transfer applications—A review. Nanomaterials 2021,11, 1628. [CrossRef] [PubMed]
177.
Said, Z.; Iqbal, M.; Mehmood, A.; Le, T.T.; Ali, H.M.; Cao, D.N.; Nguyen, P.Q.P.; Pham, N.D.K. Nanofluids-based solar collectors
as sustainable energy technology towards net-zero goal: Recent advances, environmental impact, challenges, and perspectives.
Chem. Eng. Process.-Process Intensif. 2023,191, 109477. [CrossRef]
178.
Anish, R.; Mariappan, V.; Suresh, S. Experimental investigation on melting and solidification behaviour of erythritol in a vertical
double spiral coil thermal energy storage system. Sustain. Cities Soc. 2019,44, 253–264. [CrossRef]
Energies 2024,17, 2350 34 of 35
179.
Korti, A.I.N.; Tlemsani, F.Z. Experimental investigation of latent heat storage in a coil in PCM storage unit. J. Energy Storage 2016,
5, 177–186. [CrossRef]
180.
Dinker, A.; Agarwal, M.; Agarwal, G.D. Experimental assessment on thermal storage performance of beeswax in a helical tube
embedded storage unit. Appl. Therm. Eng. 2017,111, 358–368. [CrossRef]
181.
Saydam, V.; Parsazadeh, M.; Radeef, M.; Duan, X. Design and experimental analysis of a helical coil phase change heat exchanger
for thermal energy storage. J. Energy Storage 2019,21, 9–17. [CrossRef]
182.
Rahimi, M.; Hosseini, M.J.; Gorzin, M. Effect of helical diameter on the performance of shell and helical tube heat exchanger: An
experimental approach. Sustain. Cities Soc. 2019,44, 691–701. [CrossRef]
183.
Olfian, H.; Ajarostaghi, S.S.M.; Ebrahimnataj, M. Development on evacuated tube solar collectors: A review of the last decade
results of using nanofluids. Sol. Energy 2020,211, 265–282. [CrossRef]
184.
Sankar, S.S.K.; Murugan, A.; Rahman, A.; Illyas, M.; Ramalingam, R.D.; Marquez, F.P.G.; Athikesavan, M.M. Recent advancements
in flat plate solar collector using phase change materials and nanofluid: A review. Environ. Sci. Pollut. Res. 2023,30, 88366–88386.
[CrossRef] [PubMed]
185.
Olfian, H.; Mousavi Ajarostaghi, S.S.; Ebrahimnataj, M.; Farhadi, M.; Arıcı, M. On the thermal performance of evacuated tube
solar collector integrated with phase change material. Sustain. Energy Technol. Assess. 2022,53, 20–23. [CrossRef]
186.
Mahian, O.; Kolsi, L.; Amani, M.; Estellé, P.; Ahmadi, G.; Kleinstreuer, C.; Marshall, J.S.; Majid, S. Recent advances in modeling
and simulation of nanofluid flows-Part I: Fundamentals and theory. Phys. Rep. 2019,790, 1–48. [CrossRef]
187.
Palacio, M.; Rincón, A.; Carmona, M. Experimental comparative analysis of a flat plate solar collector with and without PCM. Sol.
Energy 2020,206, 708–721. [CrossRef]
188.
Tang, R.; Cheng, Y.; Wu, M.; Li, Z.; Yu, Y. Experimental and modeling studies on thermosiphon domestic solar water heaters with
flat-plate collectors at clear nights. Energy Convers. Manag. 2010,51, 2548–2556. [CrossRef]
189.
Papadimitratos, A.; Sobhansarbandi, S.; Pozdin, V.; Zakhidov, A.; Hassanipour, F. Evacuated tube solar collectors integrated with
phase change materials. Sol. Energy 2016,129, 10–19. [CrossRef]
190.
Sardarabadi, M.; Passandideh-Fard, M.; Maghrebi, M.-J.; Ghazikhani, M. Experimental study of using both ZnO/water nanofluid
and phase change material (PCM) in photovoltaic thermal systems. Sol. Energy Mater. Sol. Cells 2017,161, 62–69. [CrossRef]
191.
Lin, S.C.; Al-Kayiem, H.H.; Bin Aris, M.S. Experimental Investigation on the Performance Enhancement of Integrated PCM-Flat
Plate Solar Collector. J. Appl. Sci. 2012,12, 2390–2396. [CrossRef]
192.
Ahmadlouydarab, M.; Ebadolahzadeh, M.; Ali, H.M. Effects of utilizing nanofluid as working fluid in a lab-scale designed FPSC
to improve thermal absorption and efficiency. Phys. A Stat. Mech. Appl. 2020,540, 123109. [CrossRef]
193.
Said, Z.; Saidur, R.; Sabiha, M.A.; Hepbasli, A.; Rahim, N.A. Energy and exergy efficiency of a flat plate solar collector using pH
treated Al2O3nanofluid. J. Clean. Prod. 2016,112, 3915–3926. [CrossRef]
194.
Chaji, H.; Ajabshirchi, Y.; Esmaeilzadeh, E.; Heris, S.Z.; Hedayatizadeh, M.; Kahani, M. Experimental study on thermal efficiency
of flat plate solar collector using TiO2/water nanofluid. Mod. Appl. Sci. 2013,7, 60–69. [CrossRef]
195.
Aggarwal, S.; Kumar, R.; Kumar, S.; Bhatnagar, M.; Kumar, P. Computational fluid dynamics based analysis for optimization
of various thermal enhancement techniques used in evacuated tubes solar collectors: A review. Mater. Today Proc. 2021,
46, 8700–8707. [CrossRef]
196.
Eltaweel, M.; Abdel-Rehim, A.A.; Attia, A.A.A. Energetic and exergetic analysis of a heat pipe evacuated tube solar collector
using MWCNT/water nanofluid. Case Stud. Therm. Eng. 2020,22, 100743. [CrossRef]
197.
Kazemian, A.; Salari, A.; Ma, T.; Lu, H. Application of hybrid nanofluids in a novel combined photovoltaic/thermal and solar
collector system. Sol. Energy 2022,239, 102–116. [CrossRef]
198.
Khodadadi, M.; Sheikholeslami, M. Heat transfer efficiency and electrical performance evaluation of photovoltaic unit under
influence of NEPCM. Int. J. Heat Mass Transf. 2022,183, 122232. [CrossRef]
199.
Tabarhoseini, S.M.; Sheikholeslami, M. Entropy generation and thermal analysis of nanofluid flow inside the evacuated tube solar
collector. Sci. Rep. 2022,12, 1380. [CrossRef]
200.
Ghaderian, J.; Che Sidik, N.A.; Kasaeian, A.; Ghaderian, S.; Okhovat, A.; Pakzadeh, A.; Samion, S.; Yahya, W.J. Performance
of copper oxide/distilled water nanofluid in evacuated tube solar collector (ETSC) water heater with internal coil under
thermosyphon system circulations. Appl. Therm. Eng. 2017,121, 520–536. [CrossRef]
201.
Al-Mashat, S.M.S.; Hasan, A.A. Evaluation of Convective Heat Transfer and Natural Circulation in an Evacuated Tube Solar
Collector. J. Eng. 2013,19, 613–628. [CrossRef]
202.
Mahbubul, I.M.; Khan, M.M.A.; Ibrahim, N.I.; Ali, H.M.; Al-Sulaiman, F.A.; Saidur, R. Carbon nanotube nanofluid in enhancing
the efficiency of evacuated tube solar collector. Renew. Energy 2018,121, 36–44. [CrossRef]
203.
Daghigh, R.; Zandi, P. Improving the performance of heat pipe embedded evacuated tube collector with nanofluids and auxiliary
gas system. Renew. Energy 2019,134, 888–901. [CrossRef]
204.
Kumar, J.; Kaushal, R. Experimental analysis of heat pipe based evacuated tube solar collector using graphene/ ethylene
glycol-water nanofluids. Energy Sources Part A Recover. Util. Environ. Eff. 2020, 1–19. [CrossRef]
205.
Ghaderian, J.; Sidik, N.A.C. An experimental investigation on the effect of Al
2
O
3
/distilled water nanofluid on the energy
efficiency of evacuated tube solar collector. Int. J. Heat Mass Transf. 2017,108, 972–987. [CrossRef]
206.
Zhu, F.; Zhang, C.; Gong, X. Numerical analysis on the energy storage efficiency of phase change material embedded in finned
metal foam with graded porosity. Appl. Therm. Eng. 2017,123, 256–265. [CrossRef]
Energies 2024,17, 2350 35 of 35
207.
Sathyamurthy, R.; Muhammad Ali, H.; Said, Z.; Kabeel, A.E.; El-Sebaey, M.S.; Gopalsamy, S.; Nagaraj, M.; Almasoud, N.; Alomar,
T.S. Enhancing solar still thermal performance: The role of surface coating and thermal energy storage in repurposed soda cans.
J. Energy Storage 2024,77, 109807. [CrossRef]
208.
Ghalambaz, M.; Shirivand, H.; Ayoubloo, K.A.; Mehryan, S.A.M.; Obai, Y.; Talebizadehsardari, P.; Yaïci, W. The Thermal Charging
Performance of Finned Conical Thermal Storage System Filled with Nano-Enhanced Phase Change Material. Molecules 2021,
26, 1605. [CrossRef] [PubMed]
209.
Nakhchi, M.E.; Hatami, M.; Rahmati, M. A numerical study on the effects of nanoparticles and stair fins on performance
improvement of phase change thermal energy storages. Energy 2021,215, 119112. [CrossRef]
210. Li, W.; Wang, Y.-H.; Kong, C.-C. Experimental study on melting/solidification and thermal conductivity enhancement of phase
change material inside a sphere. Int. Commun. Heat Mass Transf. 2015,68, 276–282. [CrossRef]
211.
Asker, M.; Alptekin, E.; Akif Ezan, M.; Ganjehsarabi, H. Entropy generation analysis of multilayer PCM slabs integrated with fins.
Int. J. Exergy 2018,26, 154–169. [CrossRef]
212.
Fan, R.; Xu, B.; Shi, L.; Zheng, N.; Sun, Z. A scalable phase change material-based system enhanced by multi-walled carbon
nanotubes and fins for efficient solar water heating applications. J. Energy Storage 2023,72, 108791. [CrossRef]
213.
Li, Z.; Shahsavar, A.; Al-Rashed, A.A.; Talebizadehsardari, P. Effect of porous medium and nanoparticles presences in a
counter-current triple-tube composite porous/nano-PCM system. Appl. Therm. Eng. 2020,167, 114777. [CrossRef]
214.
Mhiri, H.; Jemni, A.; Sammouda, H. Numerical and experimental investigations of melting process of composite material
(nanoPCM/carbon foam) used for thermal energy storage. J. Energy Storage 2020,29, 101167. [CrossRef]
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual
author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to
people or property resulting from any ideas, methods, instructions or products referred to in the content.
