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Energy efficient thermal storage montmorillonite with phase change material containing exfoliated graphite nanoplatelets
Abstract
In this experiment, we used a vacuum impregnation method to prepare shape stabilized PCM that contained sodium montmorillonite (Na-MMT) and Exfoliated graphite nanoplatelets (xGnP), to improve the thermal conductivity of PCMs, and prevent leakage of the liquid state of PCMs. Na-MMT has low cost and natural abundance, high adsorption and absorption capacities, and fire retardant heating rate. In the used materials, xGnP, usually produced from graphite intercalated compounds, are particles consisting of several layers of graphene sheets. As a result, we found that the FTIR adsorption spectra of paraffinic PCMs did not change, and there was no chemical interaction between paraffinic PCMs and xGnP/Na-MMT mixture. From the DSC analysis, xGnP made an impact on the thermal properties of the paraffinic PCMs/Na-MMT composites. The oxidation rate of paraffinic PCMs based composite with xGnP was greater than that of the composite without xGnP. FTIR, DSC, TGA and TCi were used to determine the characteristics of the paraffinic PCMs/Na-MMT composites.
... As outlined in Table 3, graphite is one of the most prevalent materials for fabricating SSPCM composites, mostly in the form of expanded graphite (EG) and exfoliated graphite nanoplatelets (xGnP), which has porous structure with high thermal conductivity. The high absorption capacity of EG and xGnP facilitates high volume incorporation of PCMs so that up to 90% by mass of composite is achievable [58][59][60][61][62][63]. For instance, Zhang et al. [62] and Kim et al. [63] used n-octadecane/EG and hexadecane/xGnP composites in the fabrication of cementitious thermal energy storage mortars, respectively. ...
... Hence, vacuum impregnation is applied to achieve the highest ratio of PCM/SM. Several researchers used this method for fabricating SSPCMs with different porous materials such as graphite powder, silica fume and diatomite [59,63,66,67,70,[73][74][75]. ...
... Melting/freezing temperature, latent heat of fusion/crystallization, and specific heat capacity of SSPCMs can be measured using DSC [62][63][64][65][66][67]. Although the phase change temperature of the SSPCM composite is in most cases equal to that of the PCM [59,62], some studies evidenced that the type of PCM and SM could alter the phase change temperature of the SSPCMs. Lv et al. showed that the melting/freezing temperature of the EG/PEG composite reduced compared to pure PEG with the increase of the EG weight percentage due to the drag effect, which prevents perfect crystallization of PEG [60]. ...
Applications of phase change materials (PCMs) have become of great interest in recent years owing to beneficial effects on the thermal, mechanical and durability properties of construction and pavement materials. PCMs can alter the thermal mass and thermal inertia of building materials, thus enhancing thermal energy storage. The effects of PCMs on cement hydration, thermal stress and shrinkage of concrete have stimulated further applications. Despite various virtues of PCMs in construction and pavement materials, their drawbacks still need concerted research efforts. Among the fundamental problems of PCMs is their risk of leakage in the melted state. Hence, several techniques have been proposed to mitigate this problem. The present study examines potential methods of incorporating PCMs into building materials, including microencapsulation, macro-encapsulation, shape-stabilization, and porous inclusion. A critical analysis of PCM applications and stabilization materials and methods in concrete is provided, hence identifying practical recommendations, research needs and current knowledge gaps.
... This research gives a broad strategy for enhancing the dosage of PCM in porous materials to enhance the energy storage capabilities of the PCM. Jeong et al. [188] increased the thermal conductivity of PCM and avoided leaking the liquid state of PCMs. They employed a vacuum impregnation approach to manufacturing form- Table 2 Comparison of recent PCM used in PV/T systems [133]. ...
... DSC curves of (a) composite PCM based on paraffinic PCM and (b) composite PCM based on xGnP, and (c) FTIR spectra of paraffinic PCM based composites[188]. ...
MXene is a new and excellent class of two-dimensional (2D) materials discovered in the last decade. The community of MXenes has drawn significant research attention because of its varied chemical structure and outstanding physicochemical characteristics in various fields, including thermal energy storage and environmental remediation applications. In the field of Material science, traditional material used in thermal energy storage devices exhibits several disadvantages, such as low thermal conductivity, reusability, cycling life and thermal storage capability. Therefore, the advanced 2D material MXene, because of various excellent characteristics , is extensively used in thermal energy storage applications. To capture thermal energy for effective use, convert solar energy to electrical or thermal energy, and store waste heat for a specific use, phase change material (PCM) may be used as a latent heat storage system. High-performance composite PCM has recently seen significant development as advanced energy storage materials. The phase change materials are extensively utilized as latent heat storage systems. PCM enables the storage of solar passive and other radiant heat as latent heat within a particular temperature, resulting in lower energy consumption, increased thermal comfort by trying to smooth out temperature changes during the day, and a decrease and shift in peak loads. Paraffin generally has a thermal conductivity in the ranges of 0.15-0.2 W/mK. It increases to 56.8 % by doping silicon nitride (Si 3 N 4) on the surface of organic phase change material paraffin. This study presents the most up-to-date, comprehensive, and trustworthy information on the role of MXene-based PCM in thermal energy storage applications. This review paper focuses on the thermal energy storage applications of 2D PCM. The thermal energy storage applications included Photovoltaic PCM, Solar water heater systems, Solar greenhouses, thermal Buildings, Cold storage, and air conditioning and refrigeration, respectively. In addition, an extensive summary of synthesis approaches of 2D materials and the effect of coating/incorpo-rating substance loading on their performance was narrated. Furthermore, a brief review of organic, inorganic and ionic liquid based PCM was elaborated. Finally, future challenges and prospects for PCM were presented before the conclusion. Finally, this comprehensive review is helpful for the advancement and application of MXenes in thermal energy storage applications.
... [90]. Few other studies have also concluded that graphite nanoparticle and various forms of graphite nanoparticles impregnation in paraffin improves the thermal conductivity [18,[89][90][91][92][93][94][95][96][97][98][99]. Nanomagnetite impregnated paraffin augmented the thermal conductivity and latent heat from 0.25 to 0.37 W/mK and 134-146 J/g respectively. ...
... Hence, care should be taken in selecting the nanoparticles for impregnation in paraffin for solar still applications since nanocomposites with improved thermal conductivity, latent heat and drop in melting point is recommended for solar still application. (ii) As we know, solar still is the economic desalination method [95,[133][134][135][136]. The selection of nanoparticles should not increase the cost per liter (CPL) of the fresh water and hence economically cheaper nanoparticles with the aforesaid properties are recommended for impregnation in paraffin for solar still applications. ...
... The latent heat is 47.1 J/g, and the thermal conductivity of the PCMs composites is 65% higher than that of paraffin [16]. It used a vacuum impregnation method to prepare shape stabilized PCMs that contained sodium montmorillonite and exfoliated graphite nanoplatelets, to improve the thermal conductivity of PCMs, and prevent leakage of the liquid state of ones [17]. ...
A thermal energy latent accumulation using phase change materials attracts interest in energy storage under an isothermal condition. An introduction of the green chemistry principles in the creation of form-stable phase change materials occupies its justified technological niche. Information about the behavior of the molecules of materials obtained using physicochemical methods including NMR spectroscopy can be used to optimize the choice of material. The materials are required longer general thermal, chemical stability and according to the thermal cycling test for the extended performance of a system. The phase changr materials with a phase transition were obtained from melts by mixing nanosized montmorillonite with carnauba wax. As a result, a number of wax/nanomaterials solid samples were prepared by grinding with a mass ratio of 70/30, 60/40 and 50/50 %. The created composite materials had the latent heat, respectively 115.5 J g for 70/30, 107.8 J/g for 60/40 and 91.4 J/g for 50/50 samples. There is a correlation between the wax content in the PCMs 70, 60 and 50 % and the percentage of heat accumulation relative to pure wax, namely 61, 57 and 48 %. The black-grey material obtained makes it possible to reduce the time intervals of the cycle of accumulation and return of heat. The profiles of heat absorption curves for all materials break off at 100 °C and the cooling curves have two regions of heat loss. The area under the DSC curves during the first heating of the powders is more on 42 % of whole pieces of PСMs. The PCMs (50/50) 13С resonances were at around 20-40 ppm, which are the typical chemical shifts for the methylene carbons of the aliphatic region, at 62.82, 63.46 ppm for the oxygenated species, at 114.05, 116.11 ppm for the alkenes at 130.68, 133.44 ppm for the aromatic rings and at 172.92, 178.72 ppm for the carboxylic groups. 27Al spectrum has the maximum at 2.90 ppm of octahedral aluminium and at 26.53 ppm may belong to a distorted tetrahedral site. Bibl. 43, Fig. 3.
... Similarly, the paraffinic Na-MMT/PCM composites combined with xGnP are also reported with the improved thermal conducting properties of PCMs. The process of vacuum impregnation for the incorporation of xGnP was used which guarantees of high heat storage capability of PCMs due to surface tension and capillary force during process of incorporation without alternating their chemical properties attributing to minimize the leakage loss (Jeong et al. 2015). ...
Phase change materials (PCM) are the best retort to the increasing energy concerns as they have the ability to store huge amounts of viable and renewable thermal energy. Conversely, their diminutive thermal conductivity and low photon absorption restrict their utilization and applicability. To eradicate these shortcomings and to upsurge their applications with greater efficiency concerning thermal power, a variety of carbon-based materials including multiwall carbon nanotubes (MWCNTs), graphene, graphite, carbon aerogel, graphene aerogel, biomass-based 3D carbon, and many others are reported. These carbon-based kinds of stuff proved the best supporting matrix to make shape alleviated carbon-based PCM hybrids for energy applications. This review highlights the fabrication techniques of the carbon-based PCM composites with respect to their application in thermal energy storage (TES) and heat transfer. In particular, the thermal transfer micro-mechanisms in carbon-based PCM composites from the perspective of lattice vibration and phonon transmission are also analyzed. Exfoliated graphite and array-oriented CNTs skeleton are found to be promising candidates for TES PCMs due to their high thermal conductivities (<7 W m⁻¹ K⁻¹). The developments in PCMs composites based on different carbon materials for advanced utilization in various fields like preparation of wearable devices, interior building designs, air-conditioning systems, and power generation are also summarized. This study will offer an inclusive overview of the PCM composites, which will be advantageous for future work with regard to the various energy concerns and sustainable development.
... To evaluate the thermal durability of the Bc-PCM and TBc-PCM, TGA analysis was carried out. GNPs were observed to have high thermal durability because thermal degradation did not occur even at 600 °C [38]. Figure 5 shows the TGA analysis of Bc-PCM and TBc-PCM. ...
The application of phase change materials (PCMs) has been verified as an effective strategy for improving energy efficiency and reducing greenhouse gas emissions. Biocomposite PCMs (Bc-PCM) exhibit large latent heat, chemical stability, and a wide temperature range. In this study, thermal conductivity improved Bc-PCM (TBc-PCM) was made via vacuum impregnation with graphene nanoplatelets (GNPs). Chemical stability analysis and thermal performance analyses of the Bc-PCM and TBc-PCM were carried out as well as building energy simulations and thermal comfort analyses. Our results show Bc-PCM showed a higher heat storage capacity and enthalpy value compared to TBc-PCM. TBc-PCM exhibited a 378% increase in thermal conductivity compared to Bc-PCM. Building energy simulation results revealed that annual heating and cooling energy consumption decreased as the thickness of the PCM layer increased. In addition, the Bc-PCM with a larger PCM capacity was more effective in reducing energy consumption during the heating period. On the other hand, the cooling energy reduction effect was greater when TBc-PCM with high thermal conductivity was applied because of the high heat transfer during the cooling period. Thermal comfort evaluation revealed it was more comfortable when PCM was applied.
... Nas últimas décadas, foram realizados vários trabalhos de investigação relacionados com a incorporação de PCM em produtos de construção, a reutilização de cinzas volantes e o impacto de altas temperaturas em materiais cimentícios (argamassas e concretos) [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Contudo, o comportamento a baixas e elevadas temperaturas de argamassas cimentícias com incorporação direta de PCM não encapsulado e cinzas volantes ainda não foi estudado. ...
Currently, it is necessary to study constructive solutions with good behavior to low and high temperatures exposure, namely that the mortar not completely lose their strength when subjected to different and more demanding temperatures than the operating temperatures. Concerning the knowledge of the phase change materials (PCM) thermal storage capacities, four different compositions based in cement and fly ash were developed inserting different contents of non-encapsulated PCM (0%, 5%, 10% and 20%), by direct incorporation. These compositions were tested to low and high temperatures (-18ºC, 20ºC, 200ºC, 400ºC and 600ºC), through freeze-thaw and compressive and flexural tests. It was possible to conclude that the incorporation of non-encapsulated PCM leads to an improvement of the behavior to the freeze-thaw tests, maintaining an identical behavior to reference mortars when subjected to high temperatures.
Keywords
Mortars; Phase Change Materials; Direct incorporation; Low temperatures; High temperatures
... After heating, the prepared mortar was placed in a cold water bath at 15 ℃ for 60 s. In the spectrum of GR, no strong peak is observed corresponding to the research [48]. In the spectrum of MMT, the peak at 3625 cm À1 represents O-H stretching vibration. ...
A novel composite phase change material (PCM) of capric-stearic acid/montmorillonite (CA-SA/MMT) with thermal conductivity enhanced by graphene (GR) was prepared. It was characterized by FT-IR, XRD, SEM, DSC and thermal conductivity tests. The temperature response of CA-SA/MMT/GR was evaluated by heating and freezing the composite PCMs in tinfoil cups. The phase change mortar containing CA-SA/MMT/2 wt%GR was also prepared, and its mechanical strength and thermal behavior were tested. The adsorption rate experiment results show that the mass ratio of CA-SA to MMT is 35:65, which can effectively prevent the leakage of PCM. The FT-IR, XRD and SEM results demonstrate that the prepared CA-SA/MMT/GR has good chemical compatibility and stability. The DSC results reveal that the CA-SA/MMT/GR has suitable phase change temperature and high latent heat, and it can retain the phase change behavior after 300 thermal cycles. The thermal conductivity of CA-SA/MMT/2 wt%GR increases by 156.4% compared with CA-SA/MMT. The heat transfer efficiency of CA-SA/MMT gradually increases with the increase of GR. The mechanical strength and thermal behavior results of phase change mortar demonstrate that the flexural strength and compressive strength decrease and the heat storage capacity increases with increasing the percentage of CA-SA/MMT/2 wt%GR.
... Chemical compatibility of composite PCMs Fig. 4(a) shows the FT-IR spectrum of GR, Dt, LA-SA, LA-SA/Dt, LA-SA/Dt/2wt%GR. In the spectrum of GR, there is no strong peak which corresponds to the research [42]. In the spectrum of Dt, the peaks at 462 cm À1 , 790 cm À1 , 1069 cm À1 represent OASiAO, SiOAH vibration and SiAOASi stretching vibration, respectively [10]. ...
The composite phase change materials (PCMs) of lauric-stearic acid/treated diatomite/graphene (LA-SA/Dt/GR) for heat storage in building envelope was prepared. It was characterized by Fourier transform infrared spectrum (FT-IR), X-ray diffraction (XRD), scanning electronic microscope (SEM), thermogravimetric analysis (TG), differential scanning calorimeter (DSC) and thermal conductivity test. The thermal performance was tested by heating and cooling the composite PCMs in tinfoil cups. The FT-IR, XRD and SEM results show that there was no chemical reaction among LA-SA, Dt and GR, and the prepared LA-SA/Dt/GR can keep its chemical stability after 1000 thermal cycles. The TG results demonstrate that the prepared LA-SA/Dt/GR has good thermal stability. The DSC results manifest that the prepared LA-SA/Dt/GR has proper temperature and high latent heat, and can keep its thermal properties after 1000 thermal cycles. The thermal conductivity results demonstrate that GR can significantly enhance the thermal conductivity of LA-SA/Dt and the thermal conductivity of LA-SA/Dt/2wt%GR has increased by 274% compared with that of LA-SA/Dt. The thermal performance results reveal that the heat transfer efficiency of LA-SA/Dt/GR increases gradually with the increasing percentage of GR. Furthermore, the phase change mortar was prepared, and the mechanical strength and thermal performance were tested. The results testify that the mechanical strength decreases with the increasing percentage of LA-SA/Dt/GR, and GR can significantly enhance the heat storage efficiency of phase change mortar.
... Graphite, as a natural non-metallic mineral, has relativity high thermal conductivity, which could be utilized as supporting material for phase change material independently and cooperatively [26]. Su-Gwang Jeong et al [27] used sodium montmorillonite and exfoliated graphite as the supporting material to prepare shaped stabilized phase change material via a vacuum impregnation method, which could improve the thermal conductivity and prevent leakage of phase change material. ...
Thermal energy storage technology plays a crucial role in the thermal management system. Clay based organic phase change material has considerable advantages in the application of thermal energy storage due to low cost and high energy storage capacity. However, the low thermal conductivity of clay, especially poor interfacial thermal transfer, limits its thermal energy storage efficiency. Herein, stearic acid/reduced graphene oxide modified montmorillonite composites (SA/RGO-MMT) were prepared by the vacuum impregnation of stearic acid into graphene modified montmorillonite matrix, which was obtained via the in situ reduction of graphene oxide on the surface of montmorillonite. Stearic acid is assembled in the porous structures of RGO-MMT with the physical interactions. SA/RGO-MMT possesses high melting enthalpy of 159 J/g, low extent of supercooling of 1.4 oC and excellent thermal reliability after 100 thermal cycling. Energy storage and release rates of SA/RGO-MMT were significantly improved due to the enhanced interfacial thermal transfer by graphene. Therefore, SA/RGO-MMT is a promising form-stable phase change material for applications in solar heat storage fields. The strategy in this study highlights the importance of enhancing interfacial thermal transfer for the efficient thermal energy storage materials.
... Taking into account the risk of PCM leakage in its liquid state, several researchers have proposed a new technique the shape-stabilization [44][45][46][47]. ...
Nowadays, the energy efficiency of buildings is one of the biggest preoccupations, due to the high negative impacts in the environment, economy and society. The utilization of phase change materials (PCM) in construction industry was been developed by several authors around the world. In this study, the connections between the PCM, energy efficiency and energy poverty are presented. The main PCM characteristics and an exhaustive description of the PCM application in buildings, more specifically in walls, floors, ceilings and glazed areas, are also presented.
... Conversely, supporting materials like high density polyethylene, diatomite, styrene-butadiene-styrene copolymer etc. have been used for shape stabilization during phase change through the polymer framework to prevent liquid leakage [7]. Clay materials such as montmorillonite have also been used to stabilize the PCM, due to their high sorption capacity which enhances the dispersion of the PCM [8]. ...
Nanocomposites consisting of paraffin/graphene nanoplatelets mix embedded in carbon foams via vacuum infiltration were fabricated with the aim of developing new phase change material (PCM) formulation with excellent shape stabilization, improved thermal conductivity and outstanding thermal reliability and structural stability. Physicochemical and thermal properties of the nanocomposites were evaluated using a suite of techniques such as scanning and transmission electron microscopy, X-ray diffraction, attenuated total reflection - Fourier transform infrared spectroscopy, nitrogen adsorption analyzer, differential scanning calorimetry, mechanical tester, Raman spectroscopy, thermal conductivity analyzer and thermogravimetric analyzer. The carbon foams exhibited good cyclic compressive behavior at a strain of up to 95% and kept part of their elastic properties after cyclic testing. Due to the robust mechanical integrity and layered meso-/macroporous morphology of these carbon foams, the nanocomposites are well equipped to cope with volume changes without leaking during thermal cycling. A 141% thermal conductivity enhancement observed for the carbon foam nanocomposite demonstrates the contributing role of the carbon foam in creating effective heat transfer through its conductive 3D network. The results have shown that proper chemical modification and subsequent carbonization of the low cost porous foams can lead to ultralight multifunctional materials with high mechanical and physical properties suitable for thermal energy storage applications.
... The difference of energy savings between VOH and POH can be affected by the indoor and outdoor conditions; the difference of those specimens is in thermal conductivity, which means that the thermal properties of the expanded vermiculite and perlite were different, and influenced the energy performance. In addition, the difference of thermal conductivity in specimens can decide the thermal performance of PCMs; this proves the various studies about the PCM with exfoliated graphite nanoplatelets (xGnP) or other materials [1][2][3][56][57][58][59] . Therefore, POH with higher thermal conductivities than VOH is considered to be efficient in winter, since higher thermal conductivities led to the efficient phase change of PCMs, compared to the heat flows to the outside. ...
Worldwide growth and the pursuit of comfort in buildings have led to significant increase in energy consumption, which is considered a current issue. Phase change material (PCM), a thermal energy storage (TES) material, is considered an effective and promising material to reduce energy consumption. In recent years, research on the application of PCM to provide higher comfort for occupants has been growing rapidly. Studies show that it is necessary to consider the optimized phase change temperature of PCMs within the comfort temperature and specific climate conditions. Thus, the objective of this study is to investigate the best optimized PCM under thermal comfort range in the climate conditions of South Korea, and analyze the energy savings of PCMs, using DesignBuilder. The prepared PCMs were n-octadecane (OT), n-heptadecane (HT), and n-hexadecane (HX), which phase change temperatures were close to the thermal comfort range. The results of the circulation water bath test showed that the phase change temperature of the mixed PCMs by OT and HT was (22–23)°C, within the thermal comfort range. According to the various mixing ratios of OT to HT, the phase change temperatures of PCMs for OH91, OH73, OH55, OH37, and OH19 appeared at ((24–26), (23–24), (22–23), (21–23), and (20-22)) °C, respectively. For energy simulation, gypsum boards with OT, OHs, and HT were prepared, and analyzed by replacing conventional gypsum board of the standard residential construction house model in South Korea. As a result, the maximum energy savings were shown by OH73 in cooling, and OH19 in heating. Consequently, the maximum total energy savings were achieved for OH73, which means that the best optimized PCM for South Korea demonstrated a phase change temperature of (23–24) °C.
... It can also be assumed that the paraffin/EPO containing GNP additive is thermally reliable, since a smaller proportion of GNP (i.e. 0.5 wt%) is used for fabrication and GNP is chemically inert, as reported in previous studies [32,42]. ...
Thermal performance of latent heat thermal energy storage (LHTES) systems is often limited by low thermal conductivity of phase change materials (PCMs), which reduces the heat transfer rate and energy storage efficiency. This study investigates the development of a thermally enhanced paraffin/hydrophobic expanded perlite (EPOP) form-stable PCM seeded with graphene nanoplatelets (GNP) as a heat transfer promoter. Experimental research was carried out on fabrication, characterization and heat transfer performance analysis of EPOP–GNP composite. It was shown that the GNP particles were partially immersed into the paraffin occupied in the pores of EPO, which remarkably improved the thermal properties and heat transfer performance of composite PCM. In comparison with EPOP, the addition of 0.5 wt% GNP increased the thermal conductivity by up to 49%. Heat transfer performance test also showed that the EPOP–GNP composite reduced the heat storage/release duration by up to 20%, compared to EPOP. Moreover, prototype test room experiment conducted on cement mortars containing EPOP–GNP revealed that the introduction GNP into form-stable PCM significantly enhanced the thermal energy storage performance of cement mortars. This is particularly demonstrated by the reduction in peak inner surface temperature of 0.8 °C and the increase in inner surface convective heat gain energy by 78%, compared to cement mortars containing EPOP only. It can be said, therefore, the integration of GNP into form-stable PCMs is a promising way to achieve high energy storage efficiency for numerous LHTES applications such as solar energy storage and energy conversation in buildings.
Phase change materials (PCMs) have attracted considerable attention as potential energy storage media for improving the energy storage densities of building envelopes. Therefore, researchers have committed to introducing PCMs into cementitious materials to develop structural–functional integrated thermal energy storage cementitious materials (TESCMs). Nevertheless, TESCMs have not been widely applied in large-scale engineering and remain in a trial or test stage. This review provides an overview of TESCMs for passive buildings to keep researchers abreast of the latest research trends and technological advances. Among the different types of PCMs, inorganic PCMs with low cost and high thermal conductivity have the most potential for application in buildings; however, their supercooling and phase separation must be addressed before use. Vacuum impregnation and micro-encapsulated and macro-encapsulated techniques are the main methods to encapsulate PCMs for preparing shape-stabilized PCMs (SSPCMs) and preventing PCM leakage from TESCMs. The inclusion of SSPCMs was found to have a negative effect on the workability, mechanical strength, and thermal conductivity of cementitious materials. However, thermal energy storage buildings (TESBs) composed of TESCMs can regulate the indoor temperature within the thermal comfort range, significantly decreasing energy consumption. This is because the effectiveness of TESBs depends highly on such factors as PCM dosages, climatic conditions, and the phase change temperature of PCMs; thus, a multi-objective optimization design is required to design TESB layouts.
Lauric acid (LA) shows much potential as one organic phase change material (PCM) for thermal energy storage, owing to its suitable melting point, relatively high thermal/chemical stability and latent heat. However, the LA-based thermal storage method invariably suffers from the big challenges of liquid leakage tendency and low thermal conductivity of single lauric acid, limiting immensely its practicality. Herein, one encapsulation and modifying strategy to fabricate high conductive and low liquid leakage composite phase change materials (CPCMs) for photo-thermal storage was proposed by constructing novel graphene doped LA/g-C3N4 CPCM. Firstly, LA is infiltrated into a novel two-dimensional porous matrix – the graphitic phase carbon nitride (g-C3N4) to prevent liquid leakage in the solid–liquid phase change process. Then it is further incorporated with a certain amount of graphite nanoplatelets to further enhance thermal conductivity. The encapsulation and modifying strategy enable the graphene doped LA/g-C3N4 to show excellent thermal storage performance for both heat and light energy, low liquid leakage, and high thermal stability. The hybrid LA/g-C3N4 with 5 wt% graphene (CPCM3) modification has a melting temperature of 45.88 °C and enthalpy of 159.19 J/g. The corresponding solidification temperature and enthalpy are 43.36 °C and 144.40 J/g, respectively. Its thermal conductivity at 50 °C is enhanced to 0.9338 W/(m·K) (one time higher than single LA), also superior to the state-of-the-art LA-based CPCMs. After 100 thermal cycles, the composite phase change material only suffers low mass loss and latent heat loss of phase change, which proves the good thermal reliability. Furthermore, TGA and DTG data indicate that CPCM3 can maintain good thermal stability in the normal operating temperature range. In the whole, the joint effect of the porous g-C3N4 matrix and graphene modification improve the thermal storage performance of LA through the improvement of liquid immobilization and thermal conductivity. This work provides a promising strategy for fabricating high conductive and low liquid-leakage CPCM toward enhanced photo-thermal storage.
The use of adequate thermal energy storage (TES) systems has shown the potential to increase energy efficiency in many fields, such as the building sector. Shape-stabilized phase change materials (SS-PCMs) have attracted attention to address one of the key barriers of phase change materials (PCMs), the leakage during the liquid state, that nowadays limits its applicability. However, SS-PCMs still have drawbacks to overcome, such as poor fire reaction and thermal stability. In the present study, polymeric SS-PCMs are nano-enhanced with layered silicates to overcome these drawbacks. The new shape-stabilized nano-enhanced phase change material (SS-NEPCM) is based on ethylene propylene diene monomer (EPDM) as a polymeric matrix, palmitic acid (PA) as PCM and montmorillonite (MMT) as the layered silicate. An innovative method based on a Banbury mixer was used to prepare it, which is an industrially scalable fabrication method. To evaluate the effect of each component, eight different formulations were prepared: pure EPDM, EPDM with MMT additions (1 wt%, 3 wt% and 5 wt%), EPDM with PA additions (5 wt% and 10 wt%) and EPDM with MMT (3 wt%) and PA additions (5 wt% and 10 wt%). The composite materials obtained were not degraded by processing as FT-IR results show. The results obtained by X-ray diffraction showed that an ordered intercalated morphology is formed between EPDM chains and MMT. Thermogravimetric experimental results revealed an increase in the thermal stability of SS-NEPCM as a result of the barrier effect provided by MMT. Moreover, SS-NEPCM fire resistance was improved with a great reduction or avoidance of the dripping phenomenon.
Sustainable construction is of paramount importance and one of the methods is deployment of phase change materials (PCMs) in construction materials due to their large latent heat capacity. This study aims at investigating the mechanical and thermal properties of non-structural lightweight concrete incorporating shape-stabilized phase change materials (SSPCMs). Toward this purpose, silica fume and polyethylene glycol 600 (PEG 600) composite was prepared with direct absorption method and no leakage was observed. Wallboards with two thicknesses including 10 % and 18 % SSPCM and macroencapsulated PCM layers were built and tested under two ambient weather conditions. Results stated that the application of SSPCM in specimens would reduce the inner-side temperature of wallboards to a great extent and the panels with less thickness had a better thermal performance. Regarding mechanical properties, tensile and compressive strength of concrete at early ages decreased by the growth of SSPCM content, while this reduction was compensated by the passage of time.
Among agricultural residues, corn cob (CC) is an essential residue of corn. Unlike common agricultural residues, CC is nutrient-dense and difficult to recycle as fertilizer or feed. Its fiber composition is similar to that of wood, allowing it to act as a wood substitute. In this study, we evaluated the usability of CC in buildings by preparing a composite board composed of CC powder and microencapsulated phase-change material (MPCM). The fibrous and porous sponge structures of CC were confirmed using field-emission scanning electron microscopy (FE-SEM). The sponge structure can be impregnated with MPCM, as confirmed by the SEM image of the CCB (corn-cob composite board with MPCM). In addition, contact angle measurements confirmed the adhesiveness of the composite board, where CCB50 showed the best adhesive strength. To determine the effect of the MPCM on the composite, the thermal performance was evaluated using differential scanning calorimetry (DSC) and dynamic thermal analysis. The DSC analysis confirmed that CCB50 had a latent heat of 20.11 J/g at a melting point of 27.8 °C, and the thermal performance was greatly improved. The temperature behavior of the specimen was investigated by heating and cooling using a heating film. During the heating process, the thermal storage effect was apparent in the temperature data of CCB25 and CCB50, and a time-delay effect was observed during the cooling process; these phenomena were clearly visible in the thermal image and were caused by the thermal preservation of the MPCM. CCB is a composite manufactured from biomaterials and can be used as a building material with high thermal performance.
Relatively weak thermal conductivity and anti-leakage performance of phase change materials (PCMs) limit their applications. The present work focuses on the development of a novel composite PCM (MP-LA/MgO/EG) based on the dispersion of expanded graphite (EG) and magnesium oxide (MgO) nanoparticles in a binary mixture of methyl palmitate-lauric acid (MP-LA). MgO/EG, a new supporting material, is assembled using expanded graphite and specially shaped MgO prepared with the surfactant-assisted high-temperature thermal decomposition method. In addition to maintaining the porous structure of EG and preventing the leakage of MP-LA, MgO/EG reduces the interface thermal resistance between the matrix and the PCM molecules because MgO maximizes heat conduction. The thermal conductivity of the proposed material (4.568 W·m⁻¹·K⁻¹) is 8.16 times higher than that of MP-LA, and its faster heat transfer rate is reflected directly in the infrared images. The enthalpy of MP-LA/MgO/EG-9 floats in a narrow range with the value of 1.88% during the process of heating-cooling cycles 100 times. The results reported herein can serve as a reference for the functional design of PCM supporting carriers that form good thermal conducting networks and provide the form-stable effect.
The effective utilization of solar energy is feasible by matching the energy supply to demand with selective solar collectors and energy storage. Solar thermal systems with thermal storage using phase change material (PCM) are beneficial in storing heat for later use. Although PCM has a high energy density due to latent heat, improving its low thermal conductivity is essential for adequate heat storage. Simultaneous improvement of thermal conductivity and maintaining the energy storage density of PCM using additives is a real challenge. The present review discusses the effects of different additives on improving the performance of nano-enhanced PCM. The additives are carbon, graphene, graphite, metals and their oxides, silicon, nanotube/fiber, graphene nanoplatelets, foam, carbon soots, zeolite, MXene, and carbonized kapok fiber. This review examines the preparation, characterization, mechanisms, factors affecting thermal conductivity, and applications of PCMs. Practical and compact energy systems with a selective combination of thermal conductivity enhancements are essential for the thermal energy needs of the domestic and industrial sectors. Few additives exhibit exceptional thermal conductivity by maintaining latent heat due to porous structure. This comprehensive review could help researchers select suitable enhancement additives to the PCM used for solar thermal applications.
As the demand for coffee has increased, by-product disposal has become a challenge to solve. Many studies are being conducted on how to use coffee waste as building materials to recycle it. In this study, the thermal performance and acoustic performance of a composite developed using bio-based microencapsulated phase change material (MPCM) and coffee waste were evaluated, and the composite was applied as building material. The coffee waste was successfully degreased with ethanol to produce composites, and removal of contaminants and oils was confirmed via scanning electron microscopy. In the phase change process of MPCM, an appropriate amount of thermal energy is absorbed and stored, and the temperature is maintained. MPCM was used in the mixture and the improved thermal performance was evaluated via differential scanning calorimetry analysis, revealing a latent heat of 3.8 J/g for MPCM content of 10%. Further, thermal imaging cameras revealed that an increase in the proportion of MPCM leads to a slower decrease in temperature because of the heat preserved by MPCM over time. In an acoustic performance evaluation, impedance tube test results showed different aspects depending on low, mid, and high-frequency bands. Specifically, at medium frequencies, which correspond to the range of noise generated in cafes, specimens fabricated using MPCM were confirmed to exhibit a higher sound absorption coefficient and an improved acoustic performance. Hence, the composite can be considered an eco-friendly building material with promising thermal and acoustic performance.
The COVID-19 pandemic has led to an increase in construction energy consumption and indoor occupancy; this, in turn, has increased the demand for energy efficiency. Thermal energy storage is an effective method for energy saving and improving efficiency. In this study, improved shape-stabilized phase change materials (SSPCMs) for enhancing the energy efficiency of buildings were manufactured and evaluated. These SSPCMs were prepared via the vacuum impregnation of n-octadecane into bentonite nanoclay. Bentonite exhibits a layered tetrahedral and octahedral crystal structure with Na⁺ cations (which feature high cation exchange capacity) in the interlayer space. The Na⁺ ion is a hydrophilic ion that affects the properties of the interlayer. However, paraffin-PCMs are hydrophobic and have poor compatibility with water. Therefore, hydrophobicity is induced in the organic nanoclay by using an organic modifier as the PCM container. Cloisite Na⁺, Cloisite 15, Cloisite 20, and Cloisite 93 were used to fabricate the SSPCMs. This study compares the amount of PCM impregnated depending on the compatibility of different PCMs between hydrophilic/hydrophobic nanoclays and also evaluates the thermal performance. The observed reduction in peak temperature and the time lag effect of the PCMs confirmed that the organically modified nanoclay and the PCM composites significantly improved the amount of PCM impregnated, thermal conductivity, and latent heat characteristics. The latent heat of the hydrophobic organic nanoclay was 209% higher than that of the SSPCM-based hydrophilic nanoclay.
Phase change materials (PCMs) have garnered intensive attention due to their high energy density and stable energy output in the field of thermal energy storage. However, the low thermal conductivity (TC) and liquid phase leakage of PCMs during phase transition significantly prevent widespread applications. Recently, two-dimensional (2D) materials are being extensively applied in improving the performance of PCMs, relying on their ultrahigh TC and excellent loading capacity. Importantly, their superior optical and electrical properties can offer PCMs with multi-responsive thermal energy conversion. This review summarizes the latest developments, emerging trends and challenges of 2D materials for advanced PCMs. We proceed from the importance of thermal energy storage and the key roles of 2D materials in the performance improvement of PCMs. Then, the fundamentals related to energy storage and thermal conduction mechanism of PCMs is systematic discussed. Further, the major preparation strategies and the major applications of 2D materials-based PCMs are emphasized in the thermal management of lithium-ion battery, solar-thermal, solar-thermal-electric and electro-thermal conversion and storage. Finally, the challenges and emerging perspectives are envisaged for deepening the future study and extending the applications of 2D materials for high-performance PCMs.
Calcium sulfate hemihydrate has been used as a building material because of its economical and non-combustible characteristics. By applying a heat storage material to a calcium sulfate hemihydrate composite (CSHC), the building energy consumption can be reduced. In this study, a CSHC with a high heat storage capacity was prepared using fine aggregates based on paraffinic shape-stabilized phase change materials (Fa-PSSPCMs) with exfoliated graphite nanoplatelets as stabilizing additives. The heat storage CSHC (Hs-CSHC) was prepared by mixing Fa-PSSPCM and calcium sulfate hemihydrate powder with water and then casting the mixture as boards using molds. For the Hs-CSHC containing 30 wt% Fa-PSSPCM, the latent heat capacities during heating and cooling were 46.39 and 44.28 J/g, respectively; its phase transition occurred at 20–35 °C. Based on analysis results, the Hs-CSHC exhibited acceptable chemical stability and high thermal performance, including a considerable latent heat capacity. The peak temperatures of Hs-CSHCs were approximately 1–2 °C lower than those of the plain CSHC. Moreover, compared with the plain CSHC, the Hs-CSHC with 30 wt% Fa-PSSPCM exhibited a time lag effect exceeding 720 min. In the energy simulation analysis, an 8.18% maximum cooling energy reduction was observed when the Hs-CSHC with 30 wt% Fa-PSSPCM was used. However, the effect of heating load reduction was insignificant due to the low outside temperature. Therefore, when a phase change material is utilized in a building, the phase change temperature and heat storage performance must be considered.
The different MSEP/SA composite phase change materials were prepared by direct impregnation method with SEP-v, SEP-p, SEP-f as supporting material. The thermal stability of the composite phase change materials was analyzed and the differences in the thermal properties and thermal reliability were compared, and provided reference for the study of different SEP to adsorb stearic acid (SA). The results indicated that there is no chemical reaction during the preparation of the composite PCMs. SEP-f has great advantages as a supporting material and its composite (65SEP-f/SA) has a good leak-proof performance with remaining mass ratio is above 99% for leakage test of 50 h. Besides, melting and freezing latent heat of three composite PCMs are similar, For 65SEP-f/SA, the melting latent heat is 76.10 J g−1 corresponds to the phase change temperature of 344.15 K and the freezing latent heat is 75.59 J g−1 corresponds to the phase change temperature of 336.85 K. The 65SEP-f/SA has the highest thermal conductivity of 0.9460 W m−1 K−1. It can be conducted that 65SEP-f/SA have great application potential in the field for low temperature phase change energy storage.
In this paper, a new series of phase change materials (PCMs) composed of capric acid/ethylene-vinyl acetate/graphene (CA/EVA/GR) were prepared and thermal properties were investigated using molecular dynamics simulation. The composite PCMs were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermal conductivity measurement. FT-IR, XRD and SEM results manifest that CA can be successfully wrapped by EVA and GR additives, and there is no chemical reaction between CA, EVA and GR. DSC results indicate that adding GR into CA/EVA can result in composite PCMs maintain the high latent heat, while too much GR will cause a significant reduction in latent heat. Thermal conductivity obtained from experimental tests reveal that GR can gradually enhance the thermal conductivity of CA/EVA with increasing dosage of GR. The experimental results of thermal conductivity fall close to that of molecular dynamics (MD) simulation at GR dosages below 1.8 wt%, but the experimental results present a trend which is contrary to MD simulation at higher GR dosages. The mean square displacement (MSD) results manifest that composite PCMs containing 1.8 wt% GR has the highest diffusion coefficient, while higher GR dosage will reduce the diffusion coefficient gradually.
The effect of reaction parameters such as amount of potassium permanganate, reaction time duration and % mass concentration of H2SO4 on volume expansion of graphite flakes to obtain mesoporous graphite was investigated. An appropriate % mass concentration of H2SO4 (65% and pH 0.38) was found to maximize volume expansion (375 ml/gm) with high surface area (100.12 m²/g) of the synthesised mesoporous graphite. The as prepared mesoporous graphite has been characterized using different techniques (p-XRD, SEM, Raman Spectroscopy and BET Analysis).
Preliminary investigation of the sorption capacity of the optimized mesoporous graphite was determined for heavy oil as function of time and weight. 4 gm (4x 1 gm pouch) was found to absorb 85% of the oil within 6 min. The absorbed oil could easily be recovered by simple filtration under decreased pressure.
The energy sector is one of the fields of interest for different nations around the world. Due to the current fossil fuel crisis, the scientific community develops new energy-saving experiences to address this concern. Buildings are one of the elements of higher energy consumption, so the generation of knowledge and technological development may offer solutions to this energy demand, which are more than welcome. Phase change materials (PCMs) included in building elements such as wall panels, blocks, panels or coatings, for heating and cooling applications have been shown, when heating, to increase the heat storage capacity by absorbing heat as latent heat. Therefore, the use of latent heat storage systems using phase change materials (PCMs) has been investigated within the last two decades. In the present review, the macro and micro encapsulation methods for construction materials are reviewed, the former being the most viable method of inclusion of PCMs in construction elements. In addition, based on the analysis of the existing papers on the encapsulation process of PCMs, the importance to pay more attention to the bio-based PCMs is shown, since more research is needed to process such PCMs. To determine its thermophysical and mechanical behavior at the micro and macro levels, in order to see the feasibility of substituting petroleum-based PCMs with a more environmentally friendly bio-based one, a section devoted to the excellent PCM with lightweight aggregate (PCM-LWA concrete) is presented due to the lack of description given in other reviews.
Form‐stable phase‐change materials (FSPCMs) are of great significance for relieving the contradiction of energy supply and demand. Unfortunately, the practical application of FSPCMs is severely compromised by their intrinsic drawbacks including lower latent heat storage (LHS) capacities, inferior interfacial compatibility, and cycling durability. Herein, we have provided a group of novel FSPCMs with higher LHS capacities, using paraffin as the LHS materials, which tightly intertwines with the 1‐octadecylamine‐modified montmorillonite (C18‐MMT) under the capillary action as well as induced dipole force due to its n‐alkyl chains compatibility. The obtained composite FSPCMs not only exhibit high melting enthalpies (137.56 J/g) but also demonstrate enhanced shape stability and thermal stability. In addition, the composites also render an impressive long‐term thermal cycling capability and structure stability even after 100 thermal cycling durability tests, which are believed to have great potential for application in the thermal management of green energy‐saving buildings.
The large-scale commercial application of phase change materials (PCMs) was seriously limited by the leakage, poor heat storage capacity and slow thermal response behavior. To address these issues, stearic acid/graphene oxide-attapulgite aerogel (SA/HGA-ATP) shape-stabilized PCMs were fabricated via hydrothermal method. The morphology, structural characteristics, thermal properties were determined and the effects of ATP percentage on the thermal properties of confined SA were studied synchronously. The nanofibers of ATP intercalated among GO sheets via grafting modification and formed fiber-bridging 3D-network. Due to the enhanced loading interspaces and suppressed volumetric shrinkage of hybrid matrix, SA/HGA-ATP exhibited excellent thermal energy storage capacity (190.9 J g⁻¹) and ultra-high SA contents (approx. 98 wt%) without leakage. The intercalated nanofibers sheltered the oxygen-containing groups of matrices, leading to the promotion of thermal energy storage performance with increase of ATP contents. Besides, the as-prepared PCMs displayed outstanding thermal response behavior because the interconnected and fiber-bridged matrices provided continuous thermal transfer pathway. Due to the protection of matrix, the composite PCMs also exhibited superior structure stability and incomparable thermal energy storage/release reliability. Considering the outstanding thermal-physical properties and low-cost of ATP, the SA/HGA-ATP has the potential to be applied in the fields of thermal energy storage, conversion and utilization.
Utilization of thermal energy storage (TES) is a solution that can be used to overcome the problem of increasing levels of energy consumption. TES is a technology to improve energy efficiency by using effective heat sources that utilize latent heat and sensible heat. Phase Change Material (PCM) is a TES material that is capable of storing large amounts of heat by using small volumes. But as a TES, PCM still has weaknesses such as low thermal conductivity and leakage during the phase change process. The solution to overcome this problem is with the Shape Stabilized Phase Change Material (SSPCM) consists of PCM and supporting materials. Based on various methods of SSPCM it is known that vacuum impregnation is a method that is capable of producing stable PCM by removing gas and moisture in the pores and then injecting PCM into its supporting material. The results obtained by treating vacuum impregnation for shape stabilized on PCM can increase the value of thermal conductivity and prevent leakage. This shows that the shape stabilized method is a very important process to produce PCM that is ready to be applied with optimal and stable characteristics.
Keywords: Phase change material Montmorillonite nanosheet Thermal energy storage Microcapsule Stearic acid A B S T R A C T In this work, a novel nanocomposite phase change material (PCM) has been designed to greatly enhance the thermal energy storage capacity and thermal conductivity. It is the first time that two-dimensional montmor-illonite nanosheets (2D-MMT) have been used in encapsulating stearic acid (SA) latex particles thus to prepare composite phase change materials (PCM), which is featured by the very thin shell and ultra-high content of active core materials. It was prepared through the self-assembly of positively charged MMT nanosheets on the negatively SA latex surfaces under a strong electrostatic attraction, leading to the formation of a core-shell structural composite PCM. The microstructure, thermal performances and cycling stability of this 2D-MMT/SA composites have been researched via Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), differential scanning calorimetry (DSC), zeta potential measurement and thermal constant analyzer. The experimental results have shown that 2D-MMT/SA composite contained an ultra-high mass fraction (> 80%) of SA due to the very thin MMT nanosheets shell, thus to have a tremendous latent heat storage capacity (184.88 J/g). In addition, the thermal conductivity of this PCM composite can reach to 159.46% of SA at most on account of the relatively high thermal conductivity of MMT nanosheets. Moreover, the protective 2D-MMT shell provided an excellent shape stability to the composite thus to restrict the leakage of PCM effectively. The composite also exhibited a stable cycling performance in the heating/cooling test. It is demonstrated that this 2D-MMT/SA composite would be of great promise for solar energy storage in sustainable energy field because of the very low cost, ultra-high latent heat storage capacity, promoted thermal conductivity, excellent structural stability and outstanding cycling performance.
Attapulgite has nanoporous structure and is an excellent supporting material for the preparation of form stable composite phase change materials (FSCPCMs). However, the effects of surface characteristics of attapulgite on the attapulgite based FSCPCMs were unclear. In this work, the effect of surface modification on the properties of different kinds of attapulgite-based FSCPCMs was investigated. First, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KH792) was used to modify attapulgite. Then, a series of FSCPCMs were prepared by adsorbing three kinds of phase change materials (PCM) with modified attapulgite (M-ATP). The crystallization and thermal properties of these FSCPCPMs were investigated. The results showed that, the surface modification improves the crystallinity and the latent heat of the FSCPCMs when paraffin or polyethylene glycol are used as the PCM. When the mass fraction of the PCM is 40%, the surface modification increases the latent heat of the paraffin/attapulgite FSCPCM and the polyethylene glycol/attapulgite FSCPCM by 31.5% and 27.8%, respectively. After 800 cooling and heating cycles, the thermal properties of paraffin/M-ATP and polyethylene glycol/M-ATP are still stable. The results were explained by analyzing the interaction between the PCM and the attapulgite. This study provides new ideas to improve the thermal properties of FSCPCMs through surface modification.
Thermal energy storage technology plays a crucial role in the thermal management system. Clay based organic phase change material has considerable advantages in the application of thermal energy storage due to low cost and high energy storage capacity. However, the low thermal conductivity of clay, especially poor interfacial thermal transfer, limits its thermal energy storage efficiency. Herein, stearic acid/reduced graphene oxide modified montmorillonite composites (SA/RGO‐MMT) were prepared by the vacuum impregnation of stearic acid into graphene modified montmorillonite matrix, which was obtained via the in situ reduction of graphene oxide on the surface of montmorillonite. Stearic acid is assembled in the porous structures of RGO‐MMT with the physical interactions. SA/RGO‐MMT possesses high melting enthalpy of 159 J/g, low extent of supercooling of 1.4 °C and excellent thermal reliability after 100 thermal cycling. Energy storage and release rates of SA/RGO‐MMT were significantly improved due to the enhanced interfacial thermal transfer by graphene. Therefore, SA/RGO‐MMT is a promising form‐stable phase change material for applications in solar heat storage fields. The strategy in this study highlights the importance of enhancing interfacial thermal transfer for the efficient thermal energy storage materials. Stearic acid/reduced graphene oxide modified montmorillonite composites were prepared by the vacuum impregnation of stearic acid into matrix. The composites possess high melting enthalpy of 159 J/g, low extent of supercooling of 1.4 °C and excellent thermal reliability after 100 thermal cycling. Energy storage and release rates of the composites were significantly improved due to the enhanced interfacial thermal transfer by graphene.
Hexagonal boron nitride (HBN) nanosheet, exfoliated by a facile Li⁺-assisted hydrothermal exfoliation method from pristine HBN, is first used as supporting material and thermal conductivity additive to prepare form-stabilized composite phase change material (PCM) by vacuum impregnation. Stearic acid (SA) was stabilized by three types of HBNs with different exfoliation degrees. Exfoliation results show that the final exfoliated HBN nanosheet exhibits maximum thickness around 5–7 nm and minimum thickness around 2–3 nm. The single-layer crystal structure is hardly destroyed and surface properties are almost no change in the exfoliation process. Furthermore, thermo-physical properties results indicate that the loading capacity of exfoliated HBN was enhanced by 32.02% compared to pristine HBN. The corresponding composite PCM has excellent chemical compatibility and thermal stability under 180 °C. Moreover, the latent heat of composite is as high as 136.20 J g⁻¹, and crystallinity is up to 98.57%, signifying almost SA in the framework of support can conduct thermal molecule movement and crystallization normally. It also indicates that the thermal conductivity of composite (0.453 W m⁻¹ K⁻¹) is enhanced by 73.36% than pure SA (0.261 W m⁻¹ K⁻¹), showing a good heat transfer efficiency. Consequently, this exfoliated HBN nanosheet possesses high loading capacity and thermal conductivity, which has the potential to prepare form-stabilized composite PCMs for thermal energy storage applications.
Recent days, the thermal energy storage (TES) is considered as a promising technology to meet the future energy demands. Thermal energy storage based on phase change material (PCM) as energy storage material due to their low cost and high storage capacity at isothermal condition. Nanoparticle dispersed in Phase Change Material (NDPCM) improves the thermal performance of base PCM by enhancing heat transfer rate during storage as well as retrieval time as demonstrated by several researchers. However, few drawbacks like thermal stability and reliability hinder their practical application at an industrial scale. The important feature of this review was that it analyses both the scientific reasons behind the increase or decrease on heat transfer rate, thermal stability, supercooling, thermal reliability and viscosity on base PCM due to the dispersion of nanoparticles as well as supporting materials into the PCM matrix and the impact of influencing parameters like size, shape, material of the nanoparticles on the thermal properties of PCM between the operating temperature range of 20–37 °C as required in low temperature applications. The reported research works ascertain that the heat transfer rate and thermal reliability of NDPCM based thermal storage system are improved and thermal stability of NDPCM is decreased by the addition of nanoparticles. It should be noted that carbon based nanoparticle has some noteworthy effects on thermal property of PCM than metal or metal oxide nanoparticles.
The objectives of this study involve evaluation of the thermal behaviors of shape-stabilization phase change material (SSPCM) manufacturing machines and SSPCM radiant floor heating (RFH) systems to determine their effectiveness in reducing building energy consumption. SSPCM manufacturing machine can produce more than 1500 g of SSPCM at a time. The advantages of this form of manufacturing include a 3-step filtered method and a two-step simple process. The mixing ratio for RFH was cement: sand: water at weight ratios of 1: 3: 0.5. Measurement results reveal that the thermal conductivity of SSPCM A_10 and A_20 increased by 107.2% and 115.84%, respectively. In thermal room analysis, A_80 case shows a heat maintenance effect of 42 min compared to A_10. Furthermore, the peak temperature is 0.4 °C higher in A_80. Additionally, more specific analysis reveals that the heat flow data presents a small input quantity of SSPCM stored thermal energy as latent heat storage (LHS). Therefore, the thermal performance of SSPCMs produced by the machine is sufficiently confirmed through experiments applied to RFH.
The development of novel materials and approaches for effective energy consumption and the employment of renewable energy sources is one of the current trends in modern material science. With this respect, the number of researches is focused on the effective harvesting and storage of solar energy for various applications. Phase change materials (PCMs) are known to be able to store thermal energy of the sunlight due to adsorption and release of latent heat through reversible phase transitions. Therefore, PCMs are promising as functional additives to construction materials and paints for advanced thermoregulation in building and industry. However, bare PCMs have limited practical applications. Organic PCMs like paraffins suffer from material leakage when undergoing in a liquid state while inorganic ones like salt hydrates lack long-term stability after multiple phase transitions. To avoid this, the loading of PCMs in porous matrices are intensively studied along with the thermal properties of the resulted composites. The loading of PCMs in microcontainers of natural porous or layered clay materials appears as a simple and cost-effective method of encapsulation significantly improving the shape and cyclic stability of PCMs. Additionally, the inclusion of functional clay containers into construction materials allows for improving their mechanical and flame-retardant properties. This article summarizes the recent progress in the preparation of composites based on PCM-loaded clay microcontainers along with their future perspectives as functional additives in thermo-regulating materials.
The use of phase change material as an efficient way to use building energy has recently been discovered as this material occupies 40 % of the total carbon emissions through energy used in the building sector. In order to apply phase change materials to buildings, phase stabilization must first be achieved; some researchers have developed shape-stabilized phase change material (SSPCM). In this study, the enthalpy-temperature function based on the thermal properties of 22 types of SSPCMs were analyzed and applied to a dynamic energy simulation program. The SSPCM was applied to improve the low heat storage performance of wooden buildings along with building energy savings. The SSPCM was applied to the inner side of a 20-mm-thick external wall in a case study concerning the inside and outside of an external wall. An analysis of the annual energy consumption of buildings showed that applying SSPCM resulted in average savings of 5 %. To confirm the improvement in the heat storage performance of buildings, the indoor temperature behavior during the heating and cooling periods was analyzed. Maintaining the thermal inertia of SSPCM was found to have reduced the peak temperature in summer by 4.1 °C.
To improve leak-proof performance of phase change materials (PCMs), hydrochloric acid-modified sepiolite (SEP) was used to encapsulate stearic acid (SA), and expanded graphite (EG) was employed as fillers to improve thermal conductivity. A series of form-stable PCMs SA/SEP and SA/SEP/EG were prepared by a combination method of direct impregnation and dry pressing with leakage tests being performed. Their crystalline structure, chemical compatibility, microstructure, latent heat, thermal stability and thermal conductivity were characterized by XRD, FT-IR, SEM, DSC, TG and thermal conductivity analysis, respectively. The leakage tests proved that the loaded mass fraction of SA in the SEP/EG could attain to 60%. The DSC experimental results showed that the composite SA60%/SEP/EG (15%) had a relative large melting latent heat of 113.7 J g−1. The thermal conductivity analysis demonstrated that the enhanced ratio of thermal conductivity in SA60%/SEP/EG (15%) was about 9 times to that of SA35%/SEP. In addition, the XRD, FT-IR, SEM and TG results indicated that the as-prepared composites were obtained by a physical mixing process with well chemical compatibility and thermal durability. Compared with the previous studies, the shape-stable SA60%/SEP/EG (15%) holds some competitive advantages.
Phase change materials (PCMs) that have the ability to convert and store solar energy could take full advantage of clean and renewable energy. However, the large-scale commercial application of PCMs was seriously limited due to the leakage, low thermal energy storage capacity and poor thermal transfer ability. In this work, natural montmorillonite (Mt) has been exfoliated into two-dimensional montmorillonite nanosheets (MtNS) and then being self-assembled into three-dimensional network montmorillonite framework (3D-MtNS), which was applied to encapsulate stearic acid (SA) for the fabrication of composite PCMs to significantly promote solar energy conversion and storage performances. This novel 3D-MtNS framework provides super porosity and huge specific surface area to encapsulate more than 95 wt% SA without leakage, resulting in the highest latent heat capacity (198.78 J/g) among clay mineral based composite PCMs. Besides, the cross-linked MtNS throughout the PCM composites provided rapid heat transfer paths, leading to outstanding thermal transfer ability and excellent photo-thermal conversion performances. In addition, due to the protection of the 3D-MtNS framework, the composite PCMs exhibit superior form stability, thermal stability and cycling stability. Compared with previous prepared clay minerals based composite PCMs, the present 3D-network MMT/SA composite PCMs showed dramatic latent heat capacity and good heat transfer ability simultaneously, which enable the direct solar energy conversion, storage and utilization.
Clay minerals are excellent supporting materials to synthesize shape-stabilized phase change materials (ssPCMs) because of outstanding pore structure, excellent thermal stability, perfect organic compatibility and eco-friendly features. However, previous clay-based ssPCMs show very low thermal energy storage capacity due to little loading of working PCMs (<65 wt%). In this work, stearic acid (SA) encapsulated by two-dimensional montmorillonite nanosheets (MtNS) has been designed in order to form core-shell structural MtNS/SA composite PCMs with ultra-high core mass fraction and dramatic latent heat capacity. This study mainly investigates the effect of MtNS shell thickness on thermal energy storage performances, including latent heat, thermal transfer ability, shape stability and cycling performances. Self-assembly mechanism of MtNS/SA was attributed to that the positively charged MtNS strongly attached on the surface of negatively charged SA latex particles and formed a core-shell structure mainly through electrostatic interaction. The MtNS/SA composite showed very large latent heat capacity (184.88 J/g) due to encapsulation of massive SA (>85 wt%). Besides, the composite PCMs also displayed improved thermal transfer ability due to the combination of MtNS, which leads to outstanding thermal charging/discharging rate and excellent photo-thermal conversion efficiency. It was also found that the thinner the MtNS, the better the thermal conductivity and latent heat storage capacity. In addition, the MtNS/SA composites show thermal and structural stability, no leakage occurred even under the encapsulation of the thinnest MtNS shell. Also, the cycling performances of this composite PCMs are very outstanding owing to the effective protection of MtNS shell. Hence, this non-leaking and green MtNS/SA composite PCMs with high-performance heat storage properties can be applied in sustainable energy field.
Energy storage plays a crucial role in saving energy and protecting the environment. The research on phase change latent heat storage materials has been in the forefront of the thermal storage research. However, the low thermal conductivity and the leakage during phase transition have limited the application of the phase change materials (PCMs). Carbon materials can be used to improve the properties of PCMs because of their excellent properties. Carbon materials have high thermal conductivity and excellent adsorption properties. Some carbon materials can improve the mechanical properties, electrical properties and flame retardant properties of PCMs. In this paper, performances and applications of one-dimensional carbon (carbon nanotubes, carbon fibers and graphite fibers) based composite PCMs, two-dimensional carbon (graphite, graphene, graphene oxide and exfoliated graphite nanoplates) based composite PCMs and three-dimensional carbon (expanded graphite, carbon based foam, graphene aerogel material and activated carbon) based composite PCMs were summarized and discussed. The advantages and disadvantages of the carbon materials with various dimensions in the application were also pointed out. References for thermal energy storage application were provided by this paper.
Fatty acids are commonly preferred as phase change materials for passive solar thermoregulation due to their several advantageous latent heat thermal energy storage (LHTES) properties. However, further storage container requirement of fatty acids against leakage problem during heating period and also low thermal conductivity significantly limit their application fields. To overcome these drawbacks of capric acid–stearic acid eutectic mixture as phase change material, it was first impregnated with expanded vermiculite clay by melting/blending method and then doped with carbon nanotubes. The effects of carbon nanotubes additive on the chemical/morphological structures and LHTES properties of the composite phase change material and thermal enhanced change phase change materials were investigated by scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry and thermogravimetric analysis analysis techniques. The differential scanning calorimetry results showed that the form-stable composite phase change materials and thermal enhanced composite phase change materials have melting temperatures in the range of 24.35–24.64℃ and latent heat capacities between 76.32 and 73.13 J/g. Thermal conductivity of the composite phase change materials was increased as 83.3, 125.0 and 258.3% by carbon nanotubes doping 1, 3 and 5 wt%. The heat charging and discharging times of the thermal enhanced -composite phase change materials were reduced appreciably due to the enhanced thermal conductivity without notably influencing their LHTES properties. Furthermore, the thermal cycling test and thermogravimetric analysis findings proved that all fabricated composites had admirable thermal durability, cycling LHTES performance and chemical stability.
Storage, transformation, and absorption of energy play effective roles in application and performance of heat and thermal energy beneficiary. Phase change materials (PCMs) are substances with high heat of fusion which can be utilized to design thermal protective and thermal energy storage systems. However, PCM leakage in phase changing process is a well-known disadvantage of the PCM containing systems. One of the approaches to avoid PCM leakage is to prepare shape-stabilized PCM in polymeric composites. In this study, polyethylene glycol (PEG), as a PCM, was shape-stabilized with low leakage in the novolac colloidal structure with no solvent and through a sol–gel in situ polymerization process. Supercooling is a negative associate phenomenon in these systems, which may occur due to the low rate of nucleation and nucleation growth. Nanoclay was used to avoid supercooling of PEG. PEG supercooling significantly decreased when 2.5 wt% of nanoclay was incorporated. This is due to the role of nanoclay particles as the crystal nuclei. The sol–gel polymerization kinetics of novolac resin in the presence of nanoclay and molten PEG was also studied using the Kamal–Sourour model. Results showed that 85 wt% of PEG was preserved with leakage less than 3.5 wt% by shape stabilization encapsulated with colloidal structure of the phenolic resin. Nanoclay improved the thermal properties of the system and reduced the supercooling about 20%. Moreover, based on Kamal–Sourour model, polymerization kinetics could suggest a lower novolac curing rate in the presence of molten PEG and nanoclay.
Photo-thermal conversion is an effective method to utilise solar energy. The generated heat can be converted into electrical energy through the thermoelectric Seebeck effect. However, the key challenge in enhancing solar-thermal-electric conversion is to achieve efficient photo-thermal conversion and temperature difference control. Herein, new composite materials are prepared using abundant and cheap raw materials to simultaneously realise photo-thermal conversion, heat storage, and heat supply for a thermoelectric device. The composites consist of carbonised waste cotton and stearic acid (SA), where carbonised waste cotton can achieve efficient full spectrum photo-thermal conversion and SA can store the generated heat to maintain a stable temperature for a thermoelectric device. The best content of SA is found to be 85 wt-% in the composites due to uniform dispersion and ideal combination. The 3D netlike structure of carbonised waste cotton provides increased heat transfer paths and also prevents leakage of SA during phase change. The maximum phase change enthalpy is 203.6 J g⁻¹ for the composite with 85 wt-% SA, which is almost the same as pure SA, assuring high density heat storage. A light-thermal-electric conversion device is further constructed based on as-prepared composites and a thermoelectric system. The generated electricity can light up a light-emitting diode with strong intensity.
Heat storage nanocomposites consisting of paraffin wax (PW) and multi-walled carbon nanotubes (MWNTs) have been prepared and their thermal properties have been investigated. Differential scanning calorimetric (DSC) results revealed that the melting point of a nanocomposite shifted to a lower temperature compared with the base material, with increasing the mass fraction of MWNTs, ϕw. With the addition of MWNTs, the latent heat capacity was reduced. The enhancement ratios in thermal conductivities of nanocomposites increase both in liquid state and in solid state with the increasing with ϕw when compared to the pure PW. For the composite with a mass fraction of 2.0%, the thermal conductivity enhancement ratios reach 35.0% and 40.0% in solid and in liquid states, respectively.
Multi-walled carbon nanotubes (CNTs) as produced are usually entangled and not ready to be dispersed into organic matrix. CNTs were treated by mechano-chemical reaction with ball milling the mixture of potassium hydroxide and the pristine CNTs. Hydroxide radical functional groups have been introduced on the CNT surfaces, which enabled to make stable and homogeneous CNT composites. Treated CNTs were successfully dispersed into the palmitic acid matrix without any surfactant. Transient short-hot-wire apparatus was used to measure the thermal conductivities of these nanotube composites. Nanotube composites have substantially higher thermal conductivities than the base palmitic acid matrix, with the enhancement increasing with the mass fraction of CNTs in both liquid state and solid state. The enhancements of the thermal conductivity are about 30% higher than the reported corresponding values for palmitic acid based phase change nanocomposites containing 1wt% CNTs treated by concentrated acid mixture.
Experimental study was carried out to study the phase change heat transfer within a composite of phase change material (PCM) infiltrated high thermal conductivity foam. An experimental setup was built to measure the temperature profiles and capture the melting evolution of the PCM inside aluminum foams. Aluminum foams were used as the porous material, and low melting temperature paraffin wax was used as the PCM. It was observed from the results that the system parameters of the wax/foam composite had a significant influence on its heat transfer behavior. By using higher porosity aluminum foam, the steady-state temperature was reached faster as compared to the foams with lower porosity. Similarly for the bigger pore size foams the steady state was attained faster as compared to the smaller pore size foams. This was due to the greater effect of convection in both the higher porosity and bigger pore size foams. However, for the lower porosity foams the heater temperature was comparatively lower than the higher porosity foams due to greater heat conduction through the foam material. Therefore, an optimal value should be selected for the foam porosity and pore size such that the effects of both conduction and convection heat transfers can be completely utilized to have a greater and improved thermal performance for the wax/aluminum foam composite.
A review is given of the academic and industrial aspects of the preparation, characterization, materials properties, crystallization behavior, melt rheology, and processing of polymer/layered silicate nanocomposites. These materials are attracting considerable interest in polymer science research. Hectorite and montmorillonite are among the most commonly used smectite-type layered silicates for the preparation of nanocomposites. Smectites are a valuable mineral class for industrial applications because of their high cation exchange capacities, surface area, surface reactivity, adsorptive properties, and, in the case of hectorite, high viscosity and transparency in solution. In their pristine form they are hydrophilic in nature, and this property makes them very difficult to disperse into a polymer matrix. The most common way to remove this difficulty is to replace interlayer cations with quarternized ammonium or phosphonium cations, preferably with long alkyl chains.
Improving the thermal performance of building envelope is an important way to save building energy consumption. The phase
change energy storage building envelope is helpful to effective use of renewable energy, reducing building operational energy
consumption, increasing building thermal comfort, and reducing environment pollution and greenhouse gas emission. This paper
presents the concept of ideal energy-saving building envelope, which is used to guide the building envelope material selection
and thermal performance design. This paper reviews some available researches on phase change building material and phase change
energy storage building envelope. At last, this paper presents some current problems needed further research.
The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy and has the advantages of high-energy storage density and the isothermal nature of the storage process. PCMs have been widely used in latent heat thermal-storage systems for heat pumps, solar engineering, and spacecraft thermal control applications. The uses of PCMs for heating and cooling applications for buildings have been investigated within the past decade. There are large numbers of PCMs that melt and solidify at a wide range of temperatures, making them attractive in a number of applications. This paper also summarizes the investigation and analysis of the available thermal energy storage systems incorporating PCMs for use in different applications.
The gap between theory and practice, in the field of adsorption, is closing. The development of new theoretical approached formulated on a molecular level, by means of computer simulation, has led to the progress of theoretical description of adsorption. New classes of solid absorbents, such as activated carbon fibers and carbon molecular sieves, fullerenes and heterofullerenes, microporous glasses and others, were developed in last 15 years. The sorption, catalytic, magnetic, optical and thermal properties of nanostructured solids has made them popular in science and technology.
Bio-based PCMs are a type of organic fatty acid ester PCMs made from natural resources, such as soy beans and palm oils. Bio-based PCMs are capable of absorbing, storing, and releasing large amounts of latent heat, similar to conventional paraffin-based PCMs. Compared to the paraffinic PCMs, Bio-based PCMs are significantly less flammable. Also they have a major drawback, namely the low thermal conductivity like as the other PCMs. To improve the thermal conductivity of Bio-based PCMs, xGnP (Exfoliated graphite nanoplatelets) can be an effective enhancement. Therefore we prepared form stable Bio-based PCMs with xGnP, by using the vacuum impregnation method. In this study, we used one of the Bio-based PCMs, which contained soybean oils, coconut oils, and beef tallow. And it has a latent heat capacity of 149.2 J/g and melting point of 29.38 °C. The Bio-based PCM was incorporated into the porous structure of xGnP. The characteristics of the Bio-based composite PCM were determined by using SEM, DSC, FTIR, TGA and TCi.
Performances of microcapsule phase change material (MPCM) for thermal energy storage are investigated. The MPCM for thermal energy storage is prepared by a complex coacervation method with gelatin and acacia as wall materials and paraffin as core material in an emulsion system. A scanning electron microscope (SEM) was used to study the microstructure of the MPCM. In thermal analysis, a differential scanning calorimeter (DSC) was employed to determine the melting temperature, melting latent heat, solidification temperature, and solidification latent heat of the MPCM for thermal energy storage. The SEM micrograph indicates that the MPCM has been successfully synthesized and that the particle size of the MPCM is about 81 μm. The DSC output results show that the melting temperature of the MPCM is 52.05 °C, the melting latent heat is 141.03 kJ/kg, the solidification temperature is 59.68 °C, and the solidification latent heat is 121.59 kJ/kg. The results prove that the MPCM for thermal energy storage has a larger phase change latent heat and suitable phase change temperature, so it can be considered as an efficient thermal energy storage material for heat utilizing systems.
The detailed understanding of the surface and interface physicochemical aspects of intercalated organo-bentonite is of importance in the design of organoclay based materials and in their industrial applications. In this study X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectra (DRIFT), X-ray diffraction (XRD) have been used to provide new insights into the surface composition, surface functional groups, interlayer structure and morphology of hexadecyl trimethyl ammonium bromide (HDTMAB)/bentonite organoclays (oMMT). Inverse gas chromatography (IGC) is used for understanding the effect of the HDTMAB on the dispersive component of the surface energy (γSd) which is closely related with the adhesion and wettability properties of materials. The increasing amount of HDTMAB in organoclays was found to significantly reduce the γSd values up to 1.5 oMMT. 1.5 oMMT and 2 oMMT values were found so closer to each other. More importantly, the γSd values were correlated with the XPS-determined surface N/Al atomic ratio, taken as a chemical descriptor for the modification of the clay.
This paper deals with the thermal performances of shape-stabilized phase change materials (SSPCM) for energy saving in various fields. This study enhanced thermal properties of SSPCM using exfoliated graphite nanoplatelets (xGnP). SSPCM, which contains the xGnP, was prepared by mixing and melting techniques for high dispersibility, thermal conductivity, and latent heat storage. In the experiment, we used hexadecane, octadecane, and paraffin as phase change materials (PCMs), and they have 254.7, 247.6, and 144.6 J g−1 of latent heat capacity, and melting points of 20.84, 30.4, and 57.09 °C, respectively. The characteristics of SSPCMs were determined using SEM, DSC, FTIR, TG, TCi, and Energy simulation. SEM morphology showed homogenous dispersion of PCM and xGnP in the porous diatomite. DSC analysis results showed the latent heat capacity of SSPCM and SSPCM/xGnP composites, and TG analysis results showed the thermal reliability of the samples. Also, we checked the thermal conductivity of the SSPCM that contains xGnP, by TCi analysis.
This study aimed determination of proper amount of paraffin (n-docosane) absorbed into expanded graphite (EG) to obtain form-stable composite as phase change material (PCM), examination of the influence of EG addition on the thermal conductivity using transient hot-wire method and investigation of latent heat thermal energy storage (LHTES) characteristics of paraffin such as melting time, melting temperature and latent heat capacity using differential scanning calorimetry (DSC) technique. The paraffin/EG composites with the mass fraction of 2%, 4%, 7%, and 10% EG were prepared by absorbing liquid paraffin into the EG. The composite PCM with mass fraction of 10% EG was considered as form-stable allowing no leakage of melted paraffin during the solid–liquid phase change due to capillary and surface tension forces of EG. Thermal conductivity of the pure paraffin and the composite PCMs including 2, 4, 7 and 10 wt% EG were measured as 0.22, 0.40, 0.52, 0.68 and 0.82 W/m K, respectively. Melting time test showed that the increasing thermal conductivity of paraffin noticeably decreased its melting time. Furthermore, DSC analysis indicated that changes in the melting temperatures of the composite PCMs were not considerable, and their latent heat capacities were approximately equivalent to the values calculated based on the mass ratios of the paraffin in the composites. It was concluded that the composite PCM with the mass fraction of 10% EG was the most promising one for LHTES applications due to its form-stable property, direct usability without a need of extra storage container, high thermal conductivity, good melting temperature and satisfying latent heat storage capacity.
The building sector is known to make a large contribution to total energy consumption and CO2 emissions. Phase change materials (PCMs) have been considered for thermal energy storage in buildings. The aim of this study was to improve the thermal conductivity of PCMs applicable as building materials using a radiant floor heating system. Using exfoliated graphite nanoplatelets (xGnP), composite PCMs were prepared by mixing and melting techniques for high dispersibility, thermal conductivity and latent heat storage. xGnP of 3 and 5 wt% was added to three types of liquid pure PCMs (octadecane, hexadecane and paraffin) with different melting points. The composite PCMs loaded with xGnP were characterized by using the SEM technique. The thermal properties of the composite PCM loaded with xGnP were determined by thermal conductivity analysis and DSC analysis. SEM morphology showed homogenous and ordered dispersion of xGnP in the three types of PCMs. The thermal conductivity of composite PCMs was increased with the xGnP loaded contents. The DSC results showed that the melting temperature and latent heat of the composite PCMs loaded with xGnP was maintained. The latent heat of composite PCMs slightly decreases when loading with xGnP. As a result, composite PCMs loaded with xGnP can be considered as energy saving building materials for a residential building using a radiant floor heating system.
Mesophase pitch based graphite foams (GFs) with different thermal properties and pore-size were used to increase the thermal diffusivity of phase change material (PCM), paraffin wax, for latent heat thermal energy storage application. To predict the performance of the Paraffin-GFs as a thermal energy storage system, their structure, thermal diffusivity and latent heat were characterized. Results indicated that thermal diffusivity of the Paraffin-GF can be enhanced 190, 270, 500, and 570 times as compared with that of pure paraffin wax. Latent heat of Paraffin-GF systems increased with the increasing of the mass ratio of the paraffin wax in the composite. Moreover, pore-size and thickness of ligaments of the foam played a key role in improving the thermal diffusivity and the storage capacity of the Paraffin-GF system: small pore-size (less paraffin wax were filled) and thicker ligament in GF resulted in a higher thermal diffusivity; large pore-size (less paraffin wax were filled) and thinner ligament in GF resulted in a larger latent heat.
Over the last years the use of phase change slurries (PCSs) based on microencapsulated phase change material (MEPCM) increased considerably due to their capacity of adaptation to various heat storage systems. PCSs are obtained by dispersing a microencapsulated PCM (particle diameter 5–20 μm) into a heat carrier fluid (e.g. water). Heat storage systems are used in applications where the available energy supply is not synchronous with the demand, such as solar thermal and waste heat recovery systems. The theoretical study conducted here – based on heat transfer and energy conservation equations – is intended to developing a theoretical model of the heat storage properties of phase change slurries capable of predicting the transient thermal response of a thermal energy storage system (TES). Most of the research work was focused on investigating the enthalpy–temperature curves resulting from a heating–cooling cycle around the melting point of the PCM. The influence of other parameters such as mico-particles diameter was assessed.
An experimental study is presented on the cement mortar incorporated with expanded graphite (EG)/paraffin composite phase change material (PCM). The composite PCM was prepared by absorbing paraffin into EG with vacuum absorption method. The heat storage cement mortar (HSCM) with proper mass fraction of the composite PCM was prepared. A testing device was designed for evaluating the heat storage effect of HSCM. Temperature variation and heat storage coefficient of HSCM were compared to those of the ordinary cement mortar (OCM). For a cubic with one HSCM board and a cubic with one OCM board, the maximum indoor center temperature difference is 2.2 K during the heat storage and 1.5 K during the heat release process. The heat storage coefficient of HSCM board is 1.74 times of that of OCM board. The results indicate that the HSCM board has good heat storage property.
New fluorescence dyes with an alkoxysilane moiety were synthesised by the condensation of 3-(triethoxysilyl)-1-propanamine (3-aminopropyltriethoxysilane) with 4,10-benzothioxanthene-3,1′-dicarboxylic acid anhydride (BTXA) and N,N-dimethylaminonaphthalene-1,8-dicarboxylic acid anhydride (DMANA), which was accompanied by the formation of an imidic bridge. The compounds N-(3-(triethoxysilyl)propyl)-thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTX-S) and 4-(N′, N′-dimethyl)-N-(triethoxysilyl)propyl-1,8-naphthalene dicarboxylic acid imide (DMAN-S) were characterised by steady-state and time-resolved fluorescence spectroscopy in chloroform and ethanol. Both conjugates (BTX-S and DMAN-S) exhibited absorption and emission bands in the same region as the un-substituted BTXA and DMANA. An important Stokes shift was observed for DMAN-S in ethanol. A high fluorescence quantum yield was observed for BTX-S in both solvents and for DMAN-S in chloroform. In addition, the newly developed fluorescent silane dyes were covalently attached to the microscopic particles of layered silicates and on the surface of SiO2 wafers as a proof of concept for fluorescence particle (surface) visualisation. The surface wafer modification was precisely characterised by X-ray photoelectron spectroscopy (XPS). Successful covalent linkage onto the particles of layered silicates was proved by confocal laser scanning microscopy technique.
Thermal energy storage (TES) systems using microencapsulated phase change material (MPCM) have been recognized as one of the most advanced energy technologies in enhancing the energy efficiency and sustainability of buildings. In this research, we examined a way to incorporate MPCMs with building materials through application for wood-based flooring. Wood-based flooring is commonly used for floor finish materials of residential buildings in Korea. There are three types of wood flooring: laminate flooring, engineered flooring and solid wood flooring. However, wood-based flooring has not performed the characteristic of heat storage. This study is aimed at manufacturing high thermal efficiency wood flooring by increasing its heat storage using MPCM. To increase the heat storage of wood-based flooring, MPCM was used with adhesive for surface bonding of wood-based flooring. As a result, this study confirmed that MPCM is dispersed well in adhesive through the scanning electron microscopy (SEM) analysis. From the differential scanning calorimetry (DSC) analysis, it can be confirmed that this composite has the characteristic of a thermal energy storage material. Also, we analyzed how this composition was formed by physical combination through the Fourier transform infrared (FT-IR) analysis. Also, we confirmed the bonding strength of the material by using the universal testing machine (UTM).
Improvements in the thermal conductivity and shape-stability of paraffin phase change materials (PCMs) by adding exfoliated graphite nanoplatelets (xGnP) or graphene were compared. The composite PCMs were fabricated by mixing paraffin with xGnP or graphene in hot toluene, followed by solvent evaporation and vacuum drying. A larger increase in thermal conductivity was observed for paraffin/xGnP, with a 10 wt.% xGnP loading producing a more than 10-fold increase. Graphene shows a lower electrical percolation threshold and offers a much larger increase in the electrical conductivity of paraffin than xGnP. However, its thermal conductivity increase is much lower. Despite the excellent thermal conductivity of single-flake graphene, the large density of nanointerfaces due to the small size of the graphene flakes significantly impedes heat transfer. We also found that graphene is much more effective than xGnP as a shape-stabilizing filler. At 2 wt.% graphene loading, paraffin maintains its shape up to 185.2 °C, well above the operating temperature range of paraffin PCMs, while the paraffin/xGnP counterpart is shape-stable up to 67.0 °C only. Small amounts of graphene and xGnP can be used in combination as a low-cost and effective improver for both the heat diffusion and shape-stabilization of paraffin PCMs.
Bacterial cellulose/polyaniline nanocomposite film was prepared by the chemical oxidative polymerization of aniline with bacterial cellulose. Polyaniline conducting polymer nanocomposite films with bacterial cellulose fibers was prepared and characterized. In nanocomposite film, the bacterial cellulose was fully encapsulated with polyaniline by direct polymerization of the respective monomers using the oxidant and dopant. These bacterial cellulose/polyaniline nanocomposite films materials exhibited the inherent properties of both components. The deposition of a polyaniline on the bacterial cellulose surface was characterized by SEM. XPS revealed a higher doping level of the nanocomposite films doped with p-TSA dopant. From the cyclic voltammetry results, the polyaniline polymer was thermodynamically stable because redox peaks of electrochemical transitions in the voltagrams were maintained in bacterial cellulose/polyaniline nanocomposite films.
Composite phase change materials (PCM) for latent heat thermal energy storage were made by mixing two different kinds of exfoliated graphite nanoplatelets (xGnP-1 and xGnP-15) into paraffin wax. Direct casting and two roll milling were used to prepare samples. The investigation on the thermal and electrical conductivity of nanocomposites with these two nanoplatelets was performed. Higher thermal conductivity of composite PCM can be achieved with nanofillers of larger aspect ratio, better orientation and lower interface density. The thermal physical properties of the nanocomposites were investigated by differential scanning calorimetry and thermal gravimetric analysis. It was found that the latent heat of the nanocomposites was not adversely affected by the presence of xGnP nanoplatelets and the thermal stability improved.
The most important factor in the worldwide problem of global warming is the emission of carbon dioxide. The 23% of carbon
dioxide emissions generated by building construction must be reduced. Reduction in thermal conductivity, especially via improved
insulation, is the most basic factor for decreasing energy consumption. Therefore, accurate and continuous thermal conductivity
measurements are important in saving energy. This study presents methods for investigating thermal conductivity measurement
and compares three methods: the heat flow meter, laser flash analysis, and thermal conductivity analyzer.
The aim of this research is to prepare a novel form-stable composite phase change material (PCM) for the latent heat thermal energy storage (LHTES) in buildings, passive solar space heating by impregnating of stearic acid (SA) into silica fume (SF) matrix through the technique of solution impregnation. The structure, thermal properties, thermal reliability, thermal conductivity and heat storage or release performance of the composite PCM were determined by scanning electron microscope (SEM), Fourier transformation infrared (FTIR), differential scanning calorimetry (DSC) and thermal cycling test analysis technique. The results show that the form-stable composite PCM has the optimal effect, preventing the leakage of SA from the composite, emerges when the SA and SF mass ratio is 1:0.9. The SA loaded on the matrix surface by physical attraction with the mass ratio of 47% during the preparation process. The latent heat of the composite PCM is measured as 82.53J/g for the melting process and 84.47J/g for the freezing process, respectively, which indicate the heat storage ability of composite is connected with the mass ratio of SA in composite. The results of DSC, FTIR and thermal cycling test are all show that the thermal reliability of the composite PCM has an imperceptible change. The increase of thermal conductivity was also confirmed by comparing the melting time, freezing time and phase change time of the composite with that of SA. All of the conclusions indicate that the composite has a better thermal conductivity and good thermal and chemical stability.
In this study, the thermal conductivity of shape-stabilized paraffin/high density polyethylene (HDPE) composite phase change material (PCM) was improved by addition of graphite powder (GP) and expanded graphite (EG). GP and EG in different mass fractions were added to PCM, and thermal conductivities of paraffin/HDPE/GP and paraffin/HDPE/EG composites were measured by a Hot Disk Thermal Constant Analyzer. An almost linear relationship between mass fractions of GP and EG additives and thermal conductivity of PCMs was found. Furthermore, the physical structures and thermal properties of the composite PCMs were investigated by scanning electron microscope (SEM) and differential scanning calorimetry (DSC), respectively. The experimental results showed that the thermal conductivities of the shape-stabilized paraffin/HDPE composite PCMs could be greatly improved by addition of EG. When the addition of EG was in the ratio of 4.6wt%, the thermal conductivity of the PCM was up to 1.36Wm−1K−1, more than 4 times of that without any additives, which was much better than that by addition of GP. The latent heat of the heat conduction enhanced PCMs decreased little due to small amount of EG, and good uniformity structure was confirmed by SEM in this paper.
The aim of this study is to prepare a novel form-stable phase change material (PCM) for latent heat thermal energy storage (LHTES) in buildings. A eutectic mixture of capric acid (CA) and myristic acid (MA) is incorporated with expanded perlite (EP). Thermal properties, thermal reliability, and thermal conductivity of the form-stable composite PCM are determined. The maximum CA–MA absorption of EP was found to be 55wt% without melted PCM seepage from the composite, and therefore this mixture was described as a form-stable composite. The form-stable composite PCM was characterized using the FT-IR spectroscopy method. The melting and freezing temperatures and latent heats of form-stable composite PCM were measured using DSC analysis. Thermal cycling test of the form-stable composite PCM indicated good thermal reliability in terms of changes in thermal properties after 5000 thermal cycling. The thermal conductivity of the form-stable CA–MA/EP composite PCM was increased about 58% by adding 10wt% expanded graphite (EG). The form-stable CA–MA/EP/EG composite PCM was considered as an effective LHTES material in the building energy conservation due to suitable phase change temperatures, high latent capacities, good thermal reliability, and good thermal conductivity.
Experimental investigation of preparation and thermal performances of paraffin/bentonite composite phase change material (PCM) are conducted. Paraffin/bentonite composite PCM are prepared by a solution intercalation process. Its composition and structure are characterized by X-ray diffraction (XRD) and scanning electronic microscope (SEM) method. The heat storage and release performances are characterized with differential scanning calorimeter instrument (DSC) curve and temperature–time curves. The results show that the layer distance of bentonite has been increased from 1.49175nm to 1.96235nm through organic modification. Paraffin can be intercalated into the layers of bentonite and be made into form-stable composite PCM. The latent heat capacity of the composite PCM is 39.84J/g. The maximum adsorption ratio of the paraffin in the composite PCM is 44.4%. DSC curve shows that the melting and freezing point of the composite PCM is 41.7°C and 43.4°C, respectively, which are approximate to that of paraffin. In addition, the heat transfer rate of prepared paraffin/bentonite composite PCM was enhanced by bentonite. The prepared composite PCM can be used in construction energy-saving and medical care.
The paraffin/expanded graphite (EG) composite phase change material (PCM) was prepared by absorbing liquid paraffin into EG, in which paraffin was chosen as the PCM. EG was produced by microwave irradiation performed at room temperature. It was found that the EG prepared at 800 W irradiation power for 10 s exhibited the maximum sorption capacity of 92 wt% for paraffin. Scanning electron microscopy images showed that paraffin was uniformly dispersed in the pores of EG. Differential scanning calorimeter analysis indicated that the melting temperature of the composite PCM was close to that of paraffin, and its latent heat was equivalent to the calculated value based on the mass fraction of paraffin in the composite. X-ray diffraction analysis showed that the composite PCM was just a combination of paraffin with EC, and no new substance was produced. Thermal energy storage performance of the composite PCM was tested in a latent thermal energy storage (LTES) system. Transients of axial and radial temperature profiles were obtained in the LTES for the composite PCM and paraffin. The thermal energy storage charging duration for the composite PCM was reduced obviously compared to paraffin.
Clays and modified clays are used to catalyze various types of organic reactions such as addition, Michael addition, carbene addition and insertion, hydrogenation, allylation, alkylation, acylation, pericyclic reactions, condensation reactions, aldol formation, imine synthesis, diazotization reactions, synthesis of heterocycles, esterification reactions, rearrangement/isomerization reactions, cyclization reactions, oxidation of alcohols, dehydrogenation, epoxidation and several more. Clays function as Brønsted and/or Lewis acids, or as bases. Clays with combined acidic and basic properties have been developed by simple procedures of modification. Such clays are employed to catalyze a sequence of acid and base-catalyzed reactions in one pot. Good enantioselectivity and stereoselectivity are achieved using chiral organic compounds and chiral complexes intercalated between clay layers. Examples from recent literature are described here.
Encapsulation of phase change materials (PCM) using a poly(methyl methacrylate) network-silica hybrid as the shell material has been developed. n-Octadecane melted at 28°C was used as PCM. Based on the suspension polymerization process, the microcapsules were prepared successfully by mixing and by the reaction of ethylene glycol dimethacrylate with precopolymer solution with tetraethoxysilane (TEOS), whose resultant microcapsules had higher latent heat (ΔH = 151 J/g) than those without TEOS (ΔH = 88.3 J/g). The average size of the PCM microcapsules was about 10 μm. The silica content, n-octadecane content, and latent heat of microcapsules were changed with varying ageing conditions, ageing time, and temperature. The highest amount of latent heat (ΔH = 178.9 J/g) and n-octadecane content (73.3%) of the microcapsule were obtained when the inorganic/organic ratio of the microcapsule was 5%. It was difficult to increase n-octadecane content (74% to 55.7–67.9%) and latent heat (180.5 J/g to 135.9–165.7 J/g) of the microcapsules by introducing different functional groups of coupling agents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
a b s t r a c t Thermal energy storage (TES) systems using phase change material (PCM) have been recognized as one of the most advanced energy technologies in enhancing the energy efficiency and sustainability of build-ings. Now the research is focus on suitable method to incorporate PCMs with building. There are several methods to use phase change materials (PCMs) in thermal energy storage (TES) for different applications. Microencapsulation is one of the well known and advanced technologies for better utilization of PCMs with building parts, such as, wall, roof and floor besides, within the building materials. Phase change materials based microencapsulation for latent heat thermal storage (LHTS) systems for building appli-cation offers a challenging option to be employed as effective thermal energy storage and a retrieval device. Since the particular interest in using microencapsulation PCMs for concrete and wall/wallboards, the specific research efforts on both subjects are reviewed separately. This paper presents an overview of the previous research work on microencapsulation technology for thermal energy storage incorporating the phase change materials (PCMs) in the building applications, along with few useful conclusive remarks concluded from the available literature.
Evaporative cooling is able to generate the cooling medium at a temperature approaching to the ambient wet bulb temperature. In this paper, a low-energy air-conditioning strategy is proposed, which is a combination of cooled ceiling (CC), microencapsulated phase change material (MPCM) slurry storage and evaporative cooling technologies. The assessment of evaporative cooling availability and utilization is done for five representative climatic cities, including Hong Kong, Shanghai, Beijing, Lanzhou and Urumqi in China, and the energy saving potential of the proposed air-conditioning system is analyzed by using a well validated building simulation code. The results indicate that the new system offers energy saving potential up to 80% under northwestern Chinese climate and up to 10% under southeastern Chinese climate. The optimal design method of the slurry storage tank is also proposed based on the slurry cooling storage behaviors and cooling demand variations of the ceiling panels.
The present paper is the first comprehensive review of the integration of phase change materials in building walls. Many considerations are discussed in this paper including physical considerations about building envelope and phase change material, phase change material integration and thermophysical property measurements and various experimental and numerical studies concerning the integration. Even if the integrated phase change material have a good potential for reducing energy demand, further investigations are needed to really assess their use.
The potential of using exfoliated graphite nanoplatelets, xGnPTM, as a reinforcement that can produce multifunctional polymer composites was explored. xGnP–polypropylene (PP) composites fabricated by melt mixing using a twin-screw extruder followed by injection molding were investigated for their thermal, viscoelastic and barrier properties as a function of xGnP concentration and aspect ratio. These properties of the xGnP–PP composites were compared to the properties of composites made with PAN-based carbon fibers, VGCF, carbon black and nanoclay. Results indicate that when oriented properly, the xGnP will not only stiffen the composite but also reduce the coefficient of thermal expansion in two directions rather than in one as in the case of aligned fiber composites. Furthermore, the large aspect ratio of xGnP, even at low loadings, increases the oxygen barrier of PP at least as effectively as the commonly used nanoclays and finally, addition of xGnP significantly enhances the thermal conductivity of the polymer matrix.
A paraffin/expanded graphite composite phase change thermal energy storage material was prepared by absorbing the paraffin into an expanded graphite that has an excellent absorbability. In such a composite, the paraffin serves as a latent heat storage material and the expanded graphite acts as the supporting material, which prevents leakage of the melted paraffin from its porous structure due to the capillary and surface tension forces. The inherent structure of the expanded graphite did not change in the composite material. The solid–liquid phase change temperature of the composite PCM was the same as that of the paraffin, and the latent heat of the paraffin/expanded graphite composite material was equivalent to the calculated value based on the mass ratio of the paraffin in the composite. The heat transfer rate of the paraffin/expanded graphite composite was obviously higher than that of the paraffin due to the combination with the expanded graphite that had a high thermal conductivity. The prepared paraffin/expanded graphite composite phase change material had a large thermal storage capacity and improved thermal conductivity and did not experience liquid leakage during its solid–liquid phase change.
An experimental energy storage system has been designed using a horizontal concentric tube heat exchanger incorporating a medium temperature phase change material (PCM) Erythritol, with a melting point of 117.7 °C. Three experimental configurations, a control system with no heat transfer enhancement and systems augmented with circular and longitudinal fins have been studied. The results presented compare the system heat transfer characteristics using isotherm plots and temperature–time curves. The system with longitudinal fins gave the best performance with increased thermal response during charging and reduced subcooling in the melt during discharging. The experimentally measured data for the control, circular finned and longitudinal finned systems have been shown to vindicate the assumption of axissymmetry (direction parallel to the heat transfer fluid flow) using temperature gradients in the axial, radial and angular directions in the double pipe PCM system.
In this work, a numerical study is proposed to investigate and predict the thermal performance of graphite foams infiltrated with phase change materials, PCMs, for space and terrestrial energy storage systems. The numerical model is based on a volume averaging technique while a finite volume method has been used to discretize the heat diffusion equation. A line-by-line solver based on tri-diagonal matrix algorithm has been used to iteratively solve the algebraic discretization equations. Because of the high thermal conductivity of graphite foams, the PCM-foam system thermal performance has been improved significantly. For space applications, the average value of the output power of the new energy storage system has been increased by more than eight times. While for terrestrial applications, the average output power using carbon foam of porosity 97% is about five times greater than that for using pure PCM.
The influence of expanded graphite (EG) and carbon fiber (CF) as heat diffusion promoters on thermal conductivity improvement of stearic acid (SA), as a phase change material (PCM), was evaluated. EG and CF in different mass fractions (2%, 4%, 7%, and 10%) were added to SA, and thermal conductivities of SA/EG and SA/CF composites were measured by using hot-wire method. An almost linear relationship between mass fractions of EG and CF additives, and thermal conductivity of SA was found. Thermal conductivity of SA (0.30 W/mK) increased by 266.6% (206.6%) by adding 10% mass fraction EG (CF). The improvement in thermal conductivity of SA was also experimentally tested by comparing melting time of the pure SA with that of SA/EG and SA/CF composites. The results indicated that the melting times of composite PCMs were reduced significantly with respect to that of pure SA. Furthermore, the latent heat capacities of the SA/EG and SA/CF (90/10 wt%) composite PCMs were determined by differential scanning calorimetry (DSC) technique and compared with that of pure SA. On the basis of all results, it was concluded that the use of EG and CF can be considered an effective method to improve thermal conductivity of SA without reducing much its latent heat storage capacity.