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Performance investigation of hybrid adsorption-compression refrigeration system accompanied with phase change materials − Intermittent characteristics
Abstract
In the current study, intermittent characteristics of hybrid adsorption-compression refrigeration systems are evaluated, notably for cold storerooms. This hybrid system utilizes ultra low-grade heat (65(C) and works with natural refrigerants. Herein, the dual-bed adsorption system operates with a working pair of silica gel/water (R718), while isobutane (R600a) is adopted for the compression system. Phase change material (PCM) is additionally incorporated to prolong the compressor off durations and improve the stabilization of the air temperature inside the cold storeroom. Mathematical modeling of the proposed systems is established using MATLAB/SIMULINK framework and validated with relevant literature. An examination of the temporal behavior of the hybrid system's leading indicators such as temperature profiles, cooling capacity, COP, electric power, and electricity demand based on the intermittent characteristics has been conducted and compared against the baseline system. The results demonstrate that the energy saving of the hybrid system during the intermittent operation mode (37%) outperforms the continuous operation mode (31.63%). Also, the hybrid system at the steady-state stage attains COP of ∼4 compared to ∼2.3 for the baseline system. However, incorporating PCM into the hybrid system abates the air temperature fluctuation inside the cold storeroom, diminishes the cyclic operations, and reduces the on-time ratio by 24.1% compared to the baseline system (34.8%) while slightly reducing the system COP. The utilization of hybrid refrigeration systems accompanied by PCM has significant profit over conventional compression systems in the market.
... Gado et al. [165] developed a mathematical model of a mini cold storage room. The studied PCM properties were those of a commercial PCM (hydrated salts), which has a PCT of − 30 • C. The PCM plates were considered to be next to the evaporator fan. ...
... (d) Experimental investigation of PCM's effect on air temperature in a domestic refrigerator [164]. (e, f) Numerical evaluation of PCM integration on temperature regulation and compressor energy consumption [165]. ...
The integration of Phase Change Materials (PCMs) as Cold Thermal Energy Storage (CTES) components represents an important advancement in refrigeration system efficiency. These materials have demonstrated significant capabilities in storing and releasing thermal energy, leading to improved system performance and reduced energy consumption. Conventional PCMs such as water/ice, hydrated salts, and paraffin are commonly used in CTES applications due to their favorable thermal properties and/or cost-effectiveness. This review paper explores the benefits and performance of integrating conventional PCMs in various refrigeration systems. It thoroughly discusses the effects of PCM integration on energy consumption, temperature stabilization, storage product quality, and greenhouse gas emissions.
While conventional PCMs are widely used in CTES applications, there is growing interest in exploring sustainable alternatives. Bio-based PCMs, derived from biomass and bio-waste materials, have shown promise as thermal storage candidates. Although these materials have been extensively studied for building applications, their potential in CTES applications remains largely unexplored. This paper also provides a detailed evaluation of bio-based materials based on their phase change temperature and latent heat, assessing their suitability for use in CTES applications.
Through this extensive review, the paper provides insights into the current state and future potential of PCM technology in CTES, highlighting both the proven benefits of conventional PCMs in enhancing refrigeration system efficiency and the potential sustainability of bio-based PCMs.
... Solar energy is widely used in various contexts, particularly in areas with high sun irradiation. Researchers investigated solar-powered sorption apparatuses, solar vapor compression refrigeration, solar glass desiccant boxes, nano sorbent, porous hydrogels, metal-organic frameworks (MOF), solar stills, etc. technologies to enhance their water production efficiency [21,[40][41][42][43][44][45][46]. The principal disadvantages of vapor compression AWH devices are their elevated power consumption and ineffectiveness in environments with low RH and temperatures. ...
... Efforts by scholars continue to be made to improve sorption chiller technology (Bhabhor and Jani 2022;Mbarek et al. 2021). While conventional MVCR-AC units dominate the air conditioning market, sorption chillers are not yet competitive (Gado et al. 2022). While scholars continue the extensive work to deliver more efficient sorption chiller and address the associated challenges (Missaoui et al. 2024), optimising the thermal load of buildings can directly support the integration of cooling systems such as sorption chillers. ...
... Its moisture absorption capacity reaches a maximum of around 0.4 g/g, at a relative humidity of 75% or higher [21]. However, it requires a high temperature, between 150-200 °C, for the water molecules to be released [22]. Unfortunately, the high temperature can also lead to a reduction in the material vapour adsorption capacity. ...
This study investigates the thermodynamic performance of various adsorbent materials used in adsorption-based atmospheric water harvesting (AWH), with a focus on their application in arid regions, such as Iraq. While significant advancements have been made in developing adsorbents capable of capturing water at low humidity levels, the lack of detailed thermodynamic analysis has hindered optimal operational conditions for these materials. The study evaluates the thermodynamic efficiencies of MOF-808, MCM-41, and COF-432, comparing their performance with other materials like MOF-801, MOF-803, and Ni2Cl2BTDD. Key findings indicate that source temperature and outlet relative humidity significantly influences system efficiency, with higher source temperatures generally improving thermal efficiency. However, lower outlet relative humidity, especially at higher temperatures, can further enhance system efficiency, emphasizing the importance of effective humidity control. Additionally, the study highlights that Iraq’s elevated ambient temperatures may exacerbate efficiency losses due to higher thermal sink temperatures, underscoring the need for adaptive design strategies. The performance of various adsorbents was found to be highly material-dependent, with certain adsorbents offering superior thermal and second-law efficiencies under specific conditions. This study offers crucial insights into optimizing adsorbent selection and system design for AWH systems, particularly in challenging climates.
... Latent heat inorganic phase change materials can capture the cold from cold ambient air at night which can be used for freecooling of inlet indoor air during the day thereby reducing the required AC power consumption and saving energy [2]. The concept has been brilliantly introduced by researchers to control indoor air temperatures and reduce the load on the air conditioning without producing any CO 2 among other applications [3][4][5][6]. However, the PCMs have shortcomings of poor heat transfer which results in undesirably long melting/solidification times, phase segregation, and poor nucleation which leads to supercooling among others [7,8]. ...
Phase change material (PCM) thermal energy storage (TES) technology is a sustainable energy savings option that is especially lucrative in building energy management. PCM(s) can be applied directly for free cooling to reduce the building energy requirement for air conditioning. However, the practical application of PCMs remains hindered by challenges of poor heat transfer which causes long charging and discharging times, incongruent phase transitions, and poor thermal stability among others. To address these challenges, this study produces a nanocomposite-PCM containing 94.25 mass% PCM-sp26, 5 mass% disodium phosphate (DSP), and 0.75 mass% graphene nanoplatelets (GnP). The composite was observed to have faster melting and solidification cycles by 12.5 and 18.5%, respectively, compared to the base PCM-sp26. Thermal reliability is presented using temperature v time graphs, and material characterizations are presented using FTIR, XRD, and SEM analyses. The composite shows improved pH by ~ 21.3%, reduced sedimentation only noticeable after + 48 h compared to 30 min for the base PCM-sp26, a narrower phase change range of 27–27.5 °C, and ~ 8% larger density. The GnP improves the melting/solidification behavior of the base PCM without significantly altering the crystalline structure and functional groups of the material. Deterioration of the latent heat is limited to ~ 24.2% only, to provide a material with a storage capacity of ~ 136.4 kJ kg−1.
... A complete analysis of STEES is modeled based on [7]. The sorption rate of the composite CaCl2-SG/water pair is governed by the linear driving force (LDF) model as follows [8]: ...
The demand for clean and renewable alternatives is rising due to the increased global warming concerns. Solar and wind energy resources offer promising solutions for power generation. Due to the natural intermittent of these resources, the use of energy storage systems, specifically in buildings, promotes grid balancing and building flexibility. The present study develops and simulates a novel sorption energy storage system for weekly storage solutions based on different charging and discharging scenarios. Various charging power of 2:10 kW with a limiting temperature of 90 °C-capitalizes on surplus solar and wind energies or off-peak electricity-is used to charge an adsorbent material (CalCl2-silica gel) up to attaining 100%SOC, at condensation temperatures of 15 and 20 °C. Subsequently, the sorption energy system discharges heating at evaporation temperatures of 10 and 15 °C. The results showed that the charging time decreased from 10.8 to 3.8 h with increasing the power from 2 to 10 kW, at a condensation temperature of 15 °C, achieving a volumetric and gravimetric energy density (ESD) of 134 kWh/m 3 and 650 kJ/kg, respectively. Overall, the use of sorption energy storage systems opens new avenues for promoting and unlocking flexibility potential and grid balancing of buildings.
... The moisture uptake capacity of silica gels reaches a maximum of approximately 0.4 g/g when the relative humidity surpasses 75% [14]. The water molecules that are bound by hydrogen bonds can be liberated by raising the temperature to 150-200 °C [28]. Elevating the temperature to a certain degree will induce dihydroxylation, leading to the elimination of silanol groups and subsequently decreasing the vapor adsorption capacity. ...
In recent decades, a consistent advancement has been observed in the extraction of water from atmospheric moisture to address the problem of water paucity, notably in arid regions. Atmospheric water harvesting (AWH) is becoming increasingly popular, particularly for distributed and decentralized applications, such as small-scale desalination facilities, which are near areas with a need for fresh water. It is operated using low-grade energy sources such as solar energy or waste heat. The present chapter covers the following aspects, (i) technologies of AWH, their major features, as well as their advantages and disadvantages, (ii) key features and types of sorption-based AWH with proper demonstration of barriers and prospects of those materials, and (iii) design and development of compact and efficient atmospheric water harvesting systems, with higher water productivity and system efficiency. Overall, atmospheric water harvesting technology could be presented as a viable candidate for abating water scarcity, for sustainable development of remote areas.
... where α and H st stand for the thermal diffusivity of aluminum and the adsorption heat, respectively. It should be highlighted that the adsorption process is exothermic [64,65]. It is worth mentioning that the heat of adsorption is added as a heat source using a user-defined function in Ansys Fluent. ...
The present study aims at improving the performance of adsorption desalination/cooling systems (ADCs) by packing the adsorbent materials inside triply periodic minimal surface (TPMS) structures. In that respect, solid and sheet types of metallic networks-based TPMS (e.g., Gyroid and Diamond) were addressed to improve the performance of ADCs. Using CFD simulations, the TPMS structures were compared to the finned tube-packed adsorbers based on specific daily water production (SDWP) and specific cooling power (SCP). The computational model was developed and hence verified using the most relevant literature. The influence of heat transfer area, effective thermal conductivity, effective diffusivity, and tortuosity on SDWP and SCP was investigated for the TPMS-derived and finned tube structures. Those structures were also examined using variant porosity levels. The results indicated that increasing TPMS porosity resulted in lower SDWP and SCP; however, TPMS still attained an improvement in SDWP and SCP compared to finned tube adsorbers. At a porosity of 0.8, SDWP of 10.4 m 3 /ton was attained by the sheet network of Diamond, which was 19.4% superior to that of the finned tube structure. At a porosity of 0.2, the sheet network of Diamond attained SDWP and SCP of 20.1 m 3 /ton and 627.4 W/kg, respectively.
... In this work, silica gel porous media was used as sorbent materials for adsorbing the water vapor from the atmospheric air. RD Silica gel was especially used for high relative humidity regions [54]. RD Silica gel (FujiSorb G-RD1030) was delivered from Fuji Silysia Chemical LTD. ...
This study proposed a scalable prototype of atmospheric water harvesting (AWH), which encompasses a triply periodic minimal surface (TPMS) structure and sorbent material. This is mainly targeted for boosting water productivity via ameliorating the heat transfer and intra/intercrystalline diffusivity inside the sorbent material (i. e., silica gel). In this respect, Gyroid as a TPMS structure was 3D-printed using AlSi10Mg powder, which has a superior surface area-to-volume ratio and elevated thermal conductivity. Additionally, the thermoelectric module was employed for dual periodic cooling and heating of the sorbent material, ensuring multi-cycling and continual water productivity. Three relative humidity levels (i.e., low, moderate, and high) were used to examine the daily water productivity and system efficiency for the AWH system with TPMS in comparison to pure sorbent. It was found that, under humid conditions (70 %RH), the utilization of TPMS indicated a daily water productivity and system efficiency of 136 L/kg m2 and 6.8%, respectively. By contrast, the AWH system without TPMS exhibited a daily water productivity and system efficiency of 74 L/kg m2 and 3.7%, respectively. Moreover, investigating the influence of the sorbent layer thickness indicated that decreasing the sorbent layer from 40 mm to 10 mm upgraded the water harvesting 1.9 times, achieving 391 L/kg m2. This is because of the lower vapor transport resistance of thinner sorbent layers. This research underscores the importance and proof-of-concept of incorporating TPMS-derived structures in sorbents to enhance the water productivity of AWH systems, thereby facilitating their transition to practical large-scale systems and increasing their feasibility for commercialization and real-world applications.
... Gado et al. [49] carried out a numerical analysis to evaluate the performance of a hybrid adsorption-compression refrigeration system for cold storage applications, utilizing natural refrigerants and ultra-low-grade heat. The system employed a dual-bed adsorption cycle with a silica gel/water (R718) working pair, and isobutane (R600a) as a refrigerant in the compression cycle. ...
A numerical analysis was performed on a hybrid cooling system consisting of an adsorption chiller (ADC) and a vapor compression chiller (VCC) operating in a cascade mode. The system was evaluated for its overall performance and energy savings compared to standalone ADC or VCC cooling systems. The ADC utilizes an RD silica gel/water working pair, while the VCC uses R410A refrigerant. The cooling strategy involves the ADC providing cooling for loads up to 10 kW, with the VCC supporting the ADC when cooling loads exceed 10 kW, up to 15 kW. MATLAB and Refprop were used to model the system, and the results were consistent with prior research. The study examined the effects of adsorption cycle time, hot water temperature, cold water temperature , adsorbent particle size, and intermediate mass flow rate. Additionally, the performance of different adsorbents, including CaCl 2 bound to mesoporous silica (SWS-1L) and Ferro-aluminophosphate (FAM-Z01), was compared to RD silica gel. The hybrid system reduced compressor work by 94.57% and 97.69% compared to conventional VCC when the hot water temperature was set to 90 • C, and cold water temperature was set to 26 • C, respectively. The hybrid system achieved the highest energy savings and overall coefficient of performance, with SWS-1L achieving a 91.37% energy savings and a 6.71 coefficient of performance. Therefore, the cascade-type hybrid cooling system is a superior alternative, particularly for cooling loads ranging from 10 kW to 23 kW, offering significant energy savings compared to conventional VCC systems.
... This equation was developed for an ambient temperature of 25-50 • C using operational data [2]. The AC power usage (W) is estimated as follows [43]: ...
One of the highest energy drains in homes and businesses is the air conditioning (AC) system. Thus, any slight improvement in the AC system performance can result in considerable energy savings. This numerical study aims to boost the AC performance in hot environments via thermal energy storage. This is accomplished by directly cooling the AC condenser using capsulated phase change materials (PCM). The PCM is capsulated in a new design of concave/convex (CX) plates to reduce the lengthy PCM solidification time and also enhance the AC performance. The PCM is solidified during a relatively low nighttime temperature and then cools the AC condenser during daytime operation. The proposed encapsulated PCM design's impact on the AC performance is assessed and compared to those of used flat plates. Using ANSYS Fluent, a mathematical equations model is developed and solved and then validated via an experimental test rig of the PCM flat plates. The effects of varying the size and number of concave/convex configurations are investigated. It is found that concave/convex PCM plates greatly minimize the solidification/melting periods compared to flat plates, making them effective in AC system daily work. Rising the CX diameter and numbers enhances the PCM melting and solidification rates and decreases the air outlet temperature. Moreover, the saved percentage of the power rises with the ambient temperature and airflow rate rising. Further, the AC power usage by adopting PCM concave/convex plates is saved by a maximum value of about 16 % and 7.5 % when working for 120 and 300 min, respectively.
... Meanwhile, ACSs operate with low-grade heat sources, low operating costs, limited maintenance, simple control, and reduced noise [5]. These advantages make it more widely used for domestic, commercial, and industrial cooling applications [6]. ...
In this study, triply periodic minimal surface (TPMS) structures have been implemented in adsorber/desorber to improve the performance of adsorption cooling systems (ACSs). The use of metal TPMS-based structures considerably increased the effective thermal conductivity of the porous media/metal composite due to its large surface area to porous media volume. A fully-three-dimensional CFD model was constructed using Ansys Fluent and validated based on relevant previous studies. Five distinct TPMS-based structures, including Gyroid, Diamond , I-graph-wrapped package, Primitive, and Lidinoid were investigated and compared with conventional Fins-based structures under different porosities, constant adsorption times, and optimal adsorption times. The specific surface area and geometric tortuosity of the adopted structures were evaluated using GeoDict software. The results demonstrated that Lidinoid attained the cyclic specific cooling power (SCP) enhancement of 12.4 % compared to Fins-based structures under the constant adsorption time of 500 s and the consistent porosity of 0.5. Meanwhile, when operated at the optimal adsorption time for each structure, Lidinoid improved the cyclic SCP by 17.5 %, while Primitive showed 6.9 % decrease in cyclic SCP compared to Fins-based structure. The cyclic SCP of TPMS structures was better than that of Fins-based structure at medium and higher porosities of 0.5 and 0.8, respectively. However, at lower porosity of 0.2, Fins-based structures outperformed TPMS structures in cyclic SCP. In terms of daily performance, Gyroid, Diamond, and Primitive structures showed faster kinetics and more potential for ACSs applications. The results indicated that Primitive structure achieved 51.6 % increase in cooling capacity per day compared to conventional Fins-based structure. In conclusion, this study has well demonstrated that the exploitation of TPMS opens new avenues for next-generation adsorption cooling applications with superior performance.
... where sensible heat (h): while PCM's latent heat (DH) is L for liquid and zero for solid. The melt fraction b is addressed as: 41,42 b ...
Air conditioning unit performance, coupled with new configurations of phase change material as thermal energy storage, is investigated in hot climates. During the daytime, the warm exterior air temperature is cooled when flowing over the phase change material structure that was previously solidified by the night ambient air. A theoretical transient model is constructed and solved numerically for the proposed design in plate and cylinder configurations. This model is studied at different inlet hot ambient air temperatures and phase change material types (SP24E and SP26E) without and with inclusion of hybrid nanoparticles. The results affirm that the discharging and charging duration for the cylinder is minimal compared to the plate configuration. Raising the inflow air temperature lowers the exit air temperature and air conditioning coefficient of performance and power-saving but shortens the cooling time. Using phase change material with a relatively low melting temperature increases the melting time and exit air temperature but reduces the charging time. Mixing hybrid nanoparticles with phase change material has a short-term positive influence on air conditioning performance. The maximum power saving for 2 h of working is 16.4% for the cylinder, while for 10 h of working, it is 6.4% for the plate.
... The current and voltage at MPP (IMPP and VMPP) depend on the open-circuit voltage, photocurrent, and weather conditions. Then, the equations used to estimate these values are introduced as follows [25][26][27][28]. Table.1 shows the used PV panel specifications [10]. ...
In this work, a hybrid system is comprised of wind turbines (WT) and photovoltaic (PV) panels to generate green Hydrogen via water electrolysis. Consideration is given to the influence of five electrical power generation scenarios on system performance and Hydrogen production cost. This study adopts the solar radiation, wind speed, and ambient temperature for Mersa-Matruh in Egypt. The system performance is studied using MATLAB-Simulink over one year. The winter months have high wind speed and low sun radiation compared to other months, whereas additional months have high solar radiation and lower wind speed than the winter months. The findings show that the amount of Hydrogen produced for all scenarios varies from 12,340 m3 to 13,748 m3 per year. The system efficiency and LCOH are 7.974% and 3.67/kg, 10.7% and 4.12 /kg, and 16.23% and 4.69.
... The heat capacity of PCM is evaluated according to the below correlation [45,46]: ...
This study highlights the PCM potential application with heat pump (HP) throughout the year under Egypt's climatic conditions. In summer, the stored cooling energy at night is used inside the hot space to reduce the HP cooling load during the daytime. However, in winter, the hot storage energy inside the PCM during the daytime reduces the HP heating load at night. RT 18 HC of 17-19°C phase change temperature is employed in building space for summer and winter, respectively. Mathematical modeling of PCM-based HP system is developed using MATLAB-Simulink and validated with literature. During summer, results demonstrate that PCM-based HP, under forced convection, significantly attains 4.6% electricity saving compared to HP without PCM. Increasing outdoor temperature from 35 to 40°C dwindles the average cooling capacity and COP from 2.8 kW and 12 to 2.6 kW and 8, respectively. There is a remarkable distinction when adopting natural convection over PCM platers rather than forced convection counterpart, highlighting 8.6% electricity saving, at 35°C ambient temperature. In winter, incorporating the same PCM inside the conditioned room reduces the energy-saving potential by 1.4%, under natural convection. PCM-based HP attains a substantial payback period of 7.9 years and carbon dioxide mitigation of 7.5 kg/year.
... where C represents the constant mushy zone. The total enthalpy (H) [39,42]: ...
Boosting the energy efficiency of air conditioning (AC) systems will considerably impact on lowering domestic power consumption. Innovative methods are being developed to enhance AC performance. One promising method involves integrating phase change materials (PCM) with the AC systems. The significant PCM charging period is a primary limitation of coupling AC systems with PCM in the previous research. The current study aims to investigate the impact of coupling an AC unit with various PCM container configurations (e.g., parallel plates, staggered and aligned tubes, and elliptical tubes) on PCM charging and discharging, and AC performance. During the nighttime, the low ambient temperature is charged inside the PCMs. Then, during the daytime, the hot ambient air is cooled by passing through the cold PCM heat exchanger before passing over the unit condenser. A complete dynamic mathematical model for the proposed system is constructed and solved numerically using ANSYS software. Results indicate that applying the cylindrical arrangement lowers the solidification time of the PCM at night by approximately one-third compared to the plate arrangement. Also, raising the inflow air temperature of the air-PCM heat exchanger increases the air temperature difference through the heat exchanger and saving percentage of the AC's power and decreases the PCM's charging and discharging time. For inflow air temperatures of 318.15 K, 313.15 K, and 308.15 K, the maximum average percentage of saved power is around 25 %, 18.7 %, and 12.5 %, respectively for 2 h working and around 8.4 %, 7.2 %, and 6.3 %, respectively for 8 h working of the AC unit. Cylindrical configuration is preferable for daily use of AC systems as the charging process can be achieved through the nighttime.
The utilization of latent heat thermal energy storage (LHTES) using phase change materials (PCM) has attracted
considerable attention due to their high energy density and thermal regulation. However, the inferior thermal
conductivity of PCM has hindered their widespread implementation, triply periodic minimal surface (TPMS)
structures could considerably ameliorate the energy storage utilization. TPMS structures offer escalated surface
area and pore interconnectivity, which can enhance the apparent thermal conductivity and improve the performance of LHTES systems. This study focuses on investigating the performance and storage capabilities of three
unique TPMS structures, namely Gyroid, IWP, and Primitive, at different relative densities and charging temperatures. The computational model is developed, verified, and validated with the relevant experiment results. A
comparative analysis of the temperature distribution and liquid fraction evolution in TPMS LHTES units is
carried out and compared to pure PCM LHTES. At a charging temperature of 80 ◦C, compared to the complete
melting time of 7206 s for the pure PCM LHTES, the results demonstrate that the G10, IWP10, and P10-PCM
LHTES achieve complete melting at 344 s, 276 s, and 368 s, respectively. This affirms the superiority of IWP
structures in improving the melting rates due to their escalated surface areas and tortuous paths. The use of TPMS
structures improves the total heat storage, heat storage rate, and volumetric heat storage density, while reducing
the gravimetric heat storage density, compared to the pure PCM LHTES. The G10-PCM LHTES attains total heat
storage, heat storage rate, volumetric, and gravimetric heat storage density of 2120 J, 6.16 W, 63.6 kWh/m3, and
227 kJ/kg, compared to 1910 J, 0.27 W, 57.3 kWh/m3, and 250 kJ/kg for pure PCM LHTES, respectively.
Moreover, increasing the relative density of TPMS structures adversely reduces the total heat storage, heat
storage rate, and volumetric heat storage density, and significantly increases the heat storage rates. As the
charging temperature increases, the complete melting time is reduced and the charging performance indicators
are improved, for the pure PCM and TPMS-PCM LHTES units.
This study focuses on the thermal management of electronic components using phase change materials (PCM) with triply periodic minimal surface (TPMS) structures. Three PCM-TPMS heat sinks (PCM-Gyroid, PCM-IWP, and PCM-Primitive) are examined, compared to pure PCM heat sinks. The heat sinks are evaluated under pulsed power sources with passive and active cooling. The effect of varying TPMS relative densities (10 %, 20 %, and 30 %) is also analyzed. The results indicate that PCM-TPMS heat sinks significantly accelerate the melting interfaces of PCM and provide improved heat transfer paths. They effectively scatter and reduce the base temperature of electronic components, with average values of 61.9 °C and 34.9 °C, compared to higher temperatures for pure PCM heat sinks under passive and active cooling, respectively. Increasing the relative density of TPMS structures from 10 % to 30 % leads to a slight improvement in base temperature reduction for the different TPMS structures. Among the three TPMS configurations, the PCM-Gyroid heat sinks are found to be the most effective in reducing base temperatures compared to PCM-IWP and PCM-Primitive heat sinks. Additionally, the use of PCM-TPMS significantly enhances the reliability and durability of electronic components by mitigating thermal cycling. Overall, the study demonstrates the potential of PCM-TPMS heat sinks in improving the thermal management and performance of electronic components.
This review highlights the latest developments of triply periodic minimal surface (TPMS) structures with the aim of the system's energy utilization. TPMS structures have gained widespread recognition due to their significant heat transfer (e.g., enhanced surface area) and diverse mechanical properties (e.g., structural stability), making them highly valuable in numerous thermal applications. A comprehensive survey of the design approaches, software tools, commercial materials, and 3D printing techniques of TPMS‐based structures is provided. Research gaps and future perspectives for the commercialization of TMPS structures are identified. Moreover, the potential applications of TPMS‐based structures for heat transfer augmentation and thermal management are discussed. TPMS‐based structures are promising topologies for heat exchangers on account of their intrinsically outstanding specific surface area. In this context, TPMS‐based structures have received considerable attention for various applications, including heat exchangers, latent heat storage, hydrogen storage, battery cooling/thermal management, and membrane distillation. Besides, distinct potential applications of TPMS‐based structures are proposed for heat transfer intensification and thermal management of photovoltaic/thermal collectors and fuel cells. Meanwhile, new proposals for using TPMS‐based structures for different sorption‐based applications, notably adsorption cooling/desalination systems, adsorption atmospheric water harvesting, thermochemical energy storage, and desiccant air conditioning, are nominated for forward‐looking perspectives.
Due to the strong dependence of the food industry on the cold chain, utilizing an optimal refrigeration facility plays a crucial role. This study focuses on the pattern of energy consumption, energy performance and exergy efficiency, and environmental effects (3E) of compression refrigeration systems used in multi-purpose cold storage. Depending on the climate and storage conditions, cooling load distribution between above and below zero evaporators significantly affects energy consumption and exergy efficiency. The limitations of each system in different cooling load demands using eco-friendly refrigerants determine that R717/R290, R290, and R134a are the optimal refrigerants for cascade, two-stage, and one-stage systems, respectively. The results show that cascade system is the least constrained operationally and technically. Its exergy efficiency is up to 4% higher than two-stage system, depending on how the refrigeration load is distributed. Two-stage system has the highest seasonal energy performance ratio (SEPR) (13% more than cascade in hot and humid climate). Its energy consumption is 18–25% less than cascade system depending on climate. Furthermore, it was found that the one-stage system is only suitable for hot and humid climates while two other systems operate well in all climates throughout the year. The amount of SEPR under cold climates for cascade system is 14% more than hot and humid climates and 3% more than moderate climates.
An experimental investigation is presented on the preparation, and characterization of nanocomposites of the phase change materials (PCM) sp24, sp26 and sp29 with Al2O3 and CuO nanoparticles (NPs). The product samples are characterized and evaluated during melting and solidification cycles. The effects of the nanoparticles in the PCMs are observed from XRD and FTIR results, sedimentation tests, color changes, density, phase change range, pH, viscosity, and rate of solidifcation and melting during thermal cycles. It is found that the product nanocomposites have increased density and viscosity compared to the base phase change fluids. The rate of melting for sp24 is improved by 18.7% when 5 wt% nanoparticles are used. Its rate of solidification is also improved by 10.5 and 14.3% with 5 wt% Al2O3 and CuO NPs, respectively. The rate of melting increases by
almost three times when 5 wt% of Al2O3 and 5 wt% of CuO are added in the same base PCM-sp26 sample. The latter nanocomposite has the best thermal performance in the study, it has an improved rate of melting at optimum melting temperature range ~22–28 ◦C suitable for thermal comfort and does not undergo any supercooling.
Freshwater scarcity is a major problem threatening many countries worldwide, notably those with arid climate conditions that lack access to fresh water. Humidity harvesting represents a reliable source of providing fresh water, especially if it can be extracted affordably and efficiently. Sorption-based atmospheric water harvesting (AWH) has the merit of being powered economically and sustainably by utilizing waste heat or solar energy compared to other AWH techniques. The first part of this chapter comprehensively presents the working principles of the atmospheric water harvesting technology. Afterward, a detailed appraisal of state-of-the-art sorption materials, such as activated carbon fiber, zeolite, silica gel, metal–organic frameworks, calcium chloride with various host materials, and hydrogels, where its adsorption isotherms and kinetics are examined in detail. The challenges and prospects of these sorption materials are also demonstrated. Moreover, numerous designs of solar-powered atmospheric water harvesters, including fixed and movable installations, are summarized and categorized. For the sake of comparison, operation concepts, advantages, disadvantages, and freshwater production capabilities are indicated. In that regard, the viability of those systems is also exhibited under different meteorological conditions. Eventually, the obstacles and limitations that hinder their utilization and future research directions are explored. Accordingly, AWH technology is introduced as a promising solution for freshwater supply, particularly in rural areas and arid deserts where water and energy are scarce.
An energetic, exergetic, economic, and environmental multicriteria evaluation of the feasibility for an integrated system comprised of an adsorption system and proton exchange membrane electrolyzer operating via photovoltaic/thermal collectors is introduced. The present system produces concurrent green hydrogen, cooling, and hot water under the meteorological conditions of Alexandria, Egypt. The generated electricity from photovoltaic/thermal collectors drives the electrolyzer for hydrogen production. The waste heat from photovoltaic/thermal collectors drives the adsorption unit during summer for cooling purposes, while in winter, it is used for domestic hot water supply. The adopted analysis is built in Simulink and consequently justified with existing literature. The transient variation of temperature profiles, cooling capacity, heating power, COP, input and output exergies, energetic and exergetic efficiencies are investigated. Investigating the daily performance of the adsorption cooling system during the summer exhibits an average daily COP of 0.47 and a system cooling capacity of about 7 kW. The results reported that the adopted system annually yields cooling, heating, and hydrogen of 8282 kWh, 1723 kWh, and 626 kg, respectively. Moreover, it is exhibited that the present system could attain annual energetic and exergetic efficiencies of 12.3% and 10.6%, respectively. The proposed system demonstrated a substantial payback period of 0.8 years and carbon dioxide mitigation of 52.2 tons. Consequently, combining the photovoltaic/thermal collectors wth adsorption cooling systems and electrolyzers could be pronouncedly appropriate for multigeneration systems.
Atmospheric water harvesting has been inexorably proliferated as a potential source of freshwater, notably for remote areas that lack access to water and electricity. This technology could be significantly operated with renewable energy sources. The current study comprehensively reviews the state-of-the-art atmospheric water harvesters and their desiccant materials. Firstly, a detailed survey on desiccant materials, silica gel, metal-organic frameworks (MOFs), hydrogels, zeolite, hygroscopic salts and composite desiccant materials is illustrated. The review particularly focuses on the materials adsorption capability, kinetics, proper matching with climate conditions. Moreover, the most suitable adsorbents are thoroughly surveyed for a wide range of climate conditions, especially for water scarcity regions (i.e., arid zones) that are characterized by low relative pressures. Moreover, various designs of solar-powered atmospheric water harvesters are comparatively summarized, including fixed and portable installations. It can be concluded that MOF-801, MOF-808, MOF-841, HKUST-1, and CPO-27(Ni) have a superior potential for water harvesting in arid areas. Additionally, MIL-101(Cr) has superior water uptake and kinetic at high relative pressure (i.e., humid areas), and it is irrelevant for water harvesting at dry zones. It is found that the cost of the collected water from atmospheric water harvesting technology is about 0.062-0.86 $/kg of adsorbent. This work provides beneficial perspectives for selecting the most relevant desiccant materials beside the appropriate solar system for water harvesting applications.
The need for innovative heating and cooling systems to decarbonize the building sector is widely recognized. It is especially important to increase the share of renewables at building level by maximizing self-consumption and reducing the primary energy demand. Accordingly, in the present paper, the results on a wide experimental campaign on a hybrid system are discussed. The system included a sorption module working as the topping cycle in a cascade configuration with a DC-driven vapor compression heat pump. A three-fluids heat exchanger with a phase change material (PCM), i.e., RT4 with nominal melting temperature of 4 °C, was installed on the evaporator side of the heat pump, for simultaneous operation as thermal storage and heat pumping purposes. The heat pump was connected to a DC-bus that included PV connection and electricity storage (batteries). Results showed that the energy efficiency of the heat pump in cascade operation was double compared to compression-only configuration and that, when simultaneously charging and discharging the latent storage in cascade configuration, no penalization in terms of efficiency compared to the compression-only configuration was measured. The self-sufficiency of the system was evaluated for three reference weeks in summer conditions of Athens climate and it was found that up to 100% of the electricity needed to drive the system could be self-produced for a modest cooling demand and up to 67% for the warmer conditions with high cooling demand.
This paper thoroughly reviews the integration of absorption, adsorption and desiccant cooling technologies into vapor compression cooling/refrigeration systems. Different configurations of hybrid absorption-compression cooling systems have been collectively listed and studied based on energetic, exergetic, economic and environmental analysis. Several reviewed studies revealed that such systems could diminish the electricity consumption by 45-88% in comparison with conventional compression systems. Besides, various arrangements of hybrid adsorption-compression cooling systems have been intensively investigated using cascade, partially integrated and fully integrated systems. These layouts of integrated adsorption-compression cooling systems focus on escalating the performance of vapor compression cooling systems by dwindling their condensation temperatures. Surveys showed that using adsorption cooling systems with oversized capacity could result in increasing the performance until approaching freezing limits, while downscaled adsorption cooling systems could worsen the system performance as a result of increasing the intermediate condensation temperature. The amalgamation of vapor compression systems with both solid and liquid desiccant cooling cycles has also been reported and compared with different regeneration schemes; for instance, electric energy, solar energy and heat rejected from the assisted vapor compression cooling systems. Considerable studies confirmed that using multi-stage solid desiccant cooling systems compared with single-stage solid desiccant cooling systems can be operated at lower regeneration temperatures. Also by introducing integrated liquid desiccant-vapor compression systems, cooling can be attained with a dehumidification process that cools the supply air lesser than its dew point with an energy provision of 30-80%. This work is beneficial for researchers involved in the field of multi-integrated cooling systems.
The energy demand of industries accounts for about 30–35% of world yearly energy consumption, a relevant percentage is due to the need of heating and cooling demand. Solar heating and cooling technologies can be integrated in industrial processes to reduce the fossil fuels consumption as well as the related greenhouse gas emissions. This paper reports the experimental analysis of a novel hybrid sorption-compression chiller for cooling and refrigeration purposes in cascade layout, which uses silica gel/water for the sorption cycle and a low Global Warming Potential (GWP) refrigerant, i.e. propylene for the compression cycle. The experimental results highlighted the flexibility of the system in terms of performances and operating conditions, these were compared to the theoretical performances and it was found out that electricity energy savings from 15% to 25% can be achieved when using the hybrid system over a compression one with the same cooling capacity. The results were converted in performance maps and processed in a statistical model, in order to get a simplified expression for determining the overall performances of the hybrid system through variables that could be measured by a final user, such as the operating temperatures. Optimization strategies were identified for a further enhancement of the performance of the chiller, i.e. the reduction of the electricity consumption, by controlling the intermediate temperature (evaporation temperature of the sorption chiller) through sorption cycle management and the use of variable speed of the pumps in all the circuits to reduce the parasitic consumption especially at low part loads.
This article aims to improve the system cooling capacity of an adsorption chiller working with a silica gel/water pair by an allocation of the optimum cycle time at different operating conditions. A mathematical model was established and validated with the literature experimental data to predict the optimum cycle time for a wide range of hot (55 °C-95 °C), cooling (25 °C-40 °C), and chilled (10 °C-22 °C) water inlet temperatures. The optimum and conventional chiller performances are compared at different operating conditions. Enhancement ratio of the system cooling capacity was tripled as the cooling water inlet temperature increased from 25 °C to 40 °C at constant hot and chilled water inlet temperatures of 85 °C and 14 °C, respectively. Applying the concept of the optimum cycle time allocation, the system cooling capacity enhancement ratio can reach 15.6% at hot, cooling, and chilled water inlet temperatures of 95 °C, 40 °C, and 10 °C, respectively.
Two polymer based sorbents PS-I and PS-II are analyzed for water sorption applications. Adsorption/desorption isotherms of water vapor onto PS-I and PS-II have been experimentally measured using a magnetic suspension adsorption measurement unit for adsorber temperature ranges 20-80 °C and evaporator temperature ranges 2-73 °C. The equilibrium adsorption uptake of water vapors corresponding to saturation condition at 30 °C by PS-I and PS-II was found nearly 2 and 2.5 times higher than the conventional silica-gel, respectively. Adsorption data has been analyzed for various adsorption models which include Brunauer-Emmett-Teller (BET); Freundlich; Dubinin-Astakhov (D-A); Oswin; and Guggenheim-Anderson-de Boer (GAB) model. The GAB and BET model give the good fit for relative pressure range of 0.10-0.90 and 0.05-0.35, respectively. At all adsorption temperatures of both sorbents, the monolayer uptake by the GAB model is found higher than the BET model. Effect of adsorption potential on adsorption uptake is highlighted in relation with water vapor adsorption mechanism. The isosteric heat of water vapor adsorption is determined for both sorbents using Clausius-Clapeyron equation.
This paper studies the effect of adding a phase change material (PCM) slab on the outside face of a refrigerator evaporator. A dynamic model of the vapour compression cycle including the presence of the phase change material and its experimental validation is presented. The simulation results of the system with PCM show that the addition of thermal inertia globally enhances heat transfer from the evaporator and allows a higher evaporating temperature, which increases the energy efficiency of the system. The energy stored in the PCM is yielded to the refrigerator cell during the off cycle and allows for several hours of continuous operation without power supply.
An assessment of the cascade adsorption-compression refrigeration system by adopting renewable energy for cold storage applications based on energy, exergy, exergoeconomic, and enviroeconomic perspectives is presented. The cascade cycle aims to dwindle the electric power of the compression subcycle with reduced condensation pressure. The thermodynamic modeling of the proposed system is developed at climatic conditions of Alexandria/Egypt for two scenarios of renewable systems, including (i) biomass-solar (Scenario-I) and (ii) biomass-solar-wind (Scenario-II). The results demonstrate that the COP of the cascade system is ameliorated by 41.6% compared to the conventional compression system; highlighting an energy saving of 42%. The proposed system has an annual average COP and exergetic efficiency of 0.122 and 1.78%, respectively for Scenario-I and 0.124 and 1.8%, respectively for Scenario-II. Scenario-I and Scenario-II deliver refrigeration at 0.235 /kWh, respectively. Herein, the exergoeconomic parameter for Scenario-I and Scenario-II is 0.70 kWh/, respectively. It is found that both scenarios alleviate about 32.75 and 5.35 tons of CO2 per annum based on environmental and exergoenvironmental standpoints, respectively. Besides, the enviroeconomic and exergoenvironmental parameters are about 474.90 /kW respectively, over the project lifespan of 20 years for both scenarios.
Flat heat pipe (HP)-phase change material (PCM) hybrid system used for
thermal regulation of simulated PV is investigated experimentally. Three
PCMs; Rubitherm RT-25 H (RT25), Rubitherm RT-35 H (RT35), and Rubitherm
RT-44 H (RT44) coupled with the HP are tested for best cooling system. Impact
of using one or two heat sinks compared with PCM only is studied. The results
show that RT25 achieves lowest PV temperature, while RT44 achieves highest
energy storage. Compared to RT25 and RT44, RT35 is considered the best for
PV cooling and PCM energy storage. Including heat sinks reduces PV temperature
and melting time and increases energy storage rate.
This study examines the energetic and economic feasibility of a new hybrid renewable biomass-solar-wind energy system for driving both cascaded adsorption-compression refrigeration systems compared with its counterpart conventional compression system for the same input energy. Two renewable energy scenarios are proposed: biomass-solar-battery (Scenario-I) and biomass-solar-wind-battery system (Scenario-II) for autonomously driving the cascaded adsorption-compression system. Herein, biomass and thermal waste heat from photovoltaic/thermal collectors are exploited for the adsorption system's operation. By contrast, the compression unit is propelled by the electric power of the photovoltaic/thermal collectors besides wind energy. In that respect, surplus electricity beyond the battery bank's charging is converted into heat through an electric heater. These scenarios are investigated and compared using representative meteorological data of New Borg El-Arab city, Egypt. The results demonstrate that Scenario-I is more cost-effective than Scenario-II, which has a cost of refrigeration of 0.235 kWh − 1 of Scenario-II. Herein, photovoltaic/thermal collectors in Scenario-I ultimately deliver 100% of the required electric load beside excess electricity of 16.6 kWh. Comparably, Scenario-II delivers surplus electricity of 15 kWh due to the designed fewer numbers of photo-voltaic/thermal collectors. Whereas biomass energy covers most of the requisite thermal demand for both scenarios. Moreover, a trade-off between the proposed cascaded adsorption-compression cycle and the renewable-based conventional compression cycle has been conducted. Herein, two proposed systems of photovoltaic-battery (Scenario-III) and photovoltaic-wind-battery (Scenario-IV) are proposed for the conventional compression cycle. The results exhibit that Scenario-III would attain a minimum annual cost of 4045 for the cascaded system, notably in Scenario-I. In general, using renewable energy mix to drive cooling/refrigeration systems could pave the way towards abating ongoing energy demands and undermining global warming and climate change impacts.
World over, research inventions have spiraled around sustainable energy solutions including the advent of phase change material based thermal energy storage systems. The application of these systems in thermo-regulating systems such as refrigeration, air conditioning, personal thermal comfort, building and construction, has been widely accepted. Most current focuses are on the topical reads of the enhancements of the phase change materials for optimized performance in thermal energy storage mechanisms. Recent publications have persistently suggested the use of nanoparticles to solve the phase change materials' low thermal-conductivity, supercooling, leakage, phase segregation and inflammability problems amongst others. This has not only shown promise of improved heat transfer and phase transition performance but also, reduced charging time and phase transition temperatures amongst many other benefits with limited distortion of other material properties. However, the process of preparing the nano-enhanced phase change material s is highly technical, requiring special equipment and precise procedures. Many studies indicated significant improvement in the phase change materials' thermal and mechanical properties when the nanomaterials were added, but some works also highlighted that the enhancement also came with a diminishing effect on the latent heat storage capacity of the phase change material. It is against these premises, that this current study does not only aim to give a detailed review of present-day advancements of nano-enhanced - phase change material but, also seeks to show how a homogenous mixture of nano-enhanced phase change material can be prepared and present the impacts of such material.
In the present study, a theoretical assessment of an adsorption-assisted cascade compression refrigeration system powered by photovoltaic/thermal collectors is performed. The proposed system is intended to produce refrigeration and electricity simultaneously. Herein, mathematical modeling of the proposed system is developed using MATLAB/SIMULINK and validated with the open literature. The impact of collector area, compressor displacement volume, cooling water temperature, and brine temperature on the system performance are quantitatively investigated and analyzed. The economic analysis of the proposed system has also been conducted. It is observed that decreasing the compressor displacement volume and cooling water temperature could substantially increase the overall coefficient of performance and energy saving. Furthermore, the results demonstrate that the system performance enhances with the increase of the collector area and the brine temperature. It is found that the proposed system can concurrently attain a daily average cooling capacity and electricity yield of 1.7 kW and 103 kWh at cooling and brine temperatures of 30 °C and -20 °C, respectively. Simulation results indicate that the proposed system can generate annual refrigeration production and electricity production of 34.4 kWhc m-2 and 213 kWhel m-2, respectively, with an annual average coefficient of performance of 2.38. Moreover, the economic analysis exhibited that the photovoltaic/thermal collectors-assisted cascade adsorption-compression system is economically competitive for refrigeration applications, revealing an annual energy saving of 24.8% and a payback period of ∼3.9 years. In this regard, cascade adsorption-compression systems could significantly extend the potential application and energy savings for cooling systems and heat pumps.
In the present study, a theoretical assessment of an adsorption-assisted cascade compression refrigeration system powered by photovoltaic/thermal collectors is performed. The proposed system is intended to produce refrigeration and electricity simultaneously. Herein, mathematical modeling of the proposed system is developed using MATLAB/SIMULINK and validated with the open literature. The impact of collector area, compressor displacement volume, cooling water temperature, and brine temperature on the system performance are quantitatively investigated and analyzed. The economic analysis of the proposed system has also been conducted. It is observed that decreasing the compressor displacement volume and cooling water temperature could substantially increase the overall coefficient of performance and energy saving. Furthermore, the results demonstrate that the system performance enhances with the increase of the collector area and the brine temperature. It is found that the proposed system can concurrently attain a daily average cooling capacity and electricity yield of 1.7 kW and 103 kWh at cooling and brine temperatures of 30 C and -20 C, respectively. Simulation results indicate that the proposed system can generate annual refrigeration production and electricity production of 34.4 kWhc m-2 and 213 kWhel m-2, respectively, with an annual average coefficient of performance of 2.38. Moreover, the economic analysis exhibited that the photovoltaic/thermal collectors-assisted cascade adsorption-compression system is economically competitive for refrigeration applications, revealing an annual energy saving of 24.8% and a payback period of 3.9 years. In this regard, cascade adsorption-compression systems could significantly extend the potential application and energy savings for cooling systems and heat pumps.
In this paper, a theoretical investigation of a solar-powered adsorption-based trigeneration system under the climate conditions of Alexandria, Egypt has been performed. The system is intended to provide the required cooling, electricity and domestic hot water (DHW) loads for a building in Alexandria throughout the year. The system comprises commercial Photovoltaic/Thermal (PVT) and Evacuated tube thermal solar collectors (ETC) for electricity production and solar thermal energy capture. A single stage double-bed silica gel/water pair-based adsorption chiller is utilized for cooling production during the summer. During winter, the captured solar thermal energy is used to provide the required DHW needs. Four different configurations of ETC-only or PVT-only solar collectors in parallel or series connection, named Conf-1 to Conf-4, have been proposed to achieve the best system performance. A novel hybrid configuration Conf-5 from ETC and PVT collectors is proposed to combine the advantages of both collector types. System performance parameters such as average cyclic cooling capacity, coefficient of performance (COP), generated electric power and overall system efficiency have been estimated for all configurations under investigation. The results of the present study show that the month of August and February have the best system performance in summer and winter, respectively. Conf-3 with ETC-only in parallel connection has the best average cooling capacity and COP of about 7.66 kW and 0.382, respectively. The month of July has the maximum electrical power generation for all three configurations containing PVT collectors with total electrical energy generation of 81.7, 78.8 and 39.9 kWh/day for Conf-1, Conf-2 and Conf-5, respectively. The average overall system efficiency for all configurations in August are about 0.315, 0.303, 0.288, 0.285 and 0.313, respectively.
A traditional adsorption refrigeration system cannot run under ultra-low grade heat source temperatures. In order for ultra-low grade heat utilization, a multi-mode integrated system of adsorption refrigeration using desiccant coated heat exchangers (DCHEs) is proposed. The key point of this integrated system is the rise in evaporation temperature by the use of DCHEs, which contributes to lowing the driving temperature and enhancing the system performance. A mathematical model based on the first and second law of thermodynamics perspective is developed, and the performance investigation is conducted to understand the effect of different modes, driving and medium temperatures. The results reveal that Mode 1 has a wider working range, Mode 2 has better performance and Mode 3 can realize the cogeneration of chilled water and dehumidified air. Compared to a traditional system, the integrated system has obviously lower driving temperature and higher performance. The integrated system with Modes 1 and 2 can operate effectively at driving temperatures below 50 oC and its maximum COP and exergetic efficiency can reach around 0.8 and 0.21, respectively. For ultra-low grade heat utilization, the medium temperature has a greater effect on the COP and equal effect on the exergetic efficiency to driving temperature.
An energy cascade utilization system is an advanced technology that recoveries waste heat energy efficiently. However, research on cascade systems by utilizing waste hot water with 60–100 °C is still considerably lacking in the literature. Specifically, this paper investigates the waste heat recovery performance of a multistage coupled absorption chiller (ABC)-adsorption chiller (ADC) cascade system. The proposed ABC-ADC cascade system is capable of producing potable water and three streams of chilled water under different temperature settings. Firstly, the experimental analysis is judiciously carried out on a four-bed two-evaporator ADC subsystem prototype. Key results reveal that the ADC’s maximum specific daily water production is 10.5 m3/day/ton. Subsequently, the ABC-ADC cascade system’s performance is experimentally analysed and optimized. The achievable maximum cooling coefficient of performance (COPc) is obtained to be 0.55. Additionally, a general method is proposed to optimize the subsystem’s cooling capacity combination of the ABC-ADC cascade system in search of an optimal COPc. The results indicate that the optimized COPc can further be enhanced by around 20%. The performance efficiency of an optimized ABC-ADC cascade system incorporating a microturbine system is then investigated. Compared to the experimental ABC-ADC cascade system, the optimized system’ total coefficient of performance is demonstrated to improve by 18%. The primary energy saving ratio is also promoted from 9.8% to 18%. Moreover, 68.92% of the gas turbine’s dissipated energy is able to be recovered by the optimized ABC-ADC system. As far as application is concerned, this cascade system has been demonstrated to be superior to standalone heat-driven chillers with great commercial potential for implementation in industries where low-grade waste heat is readily available.
This study theoretically investigates the energetic and economic feasibility of three configurations of a solar-driven hybrid adsorption-compression cooling system using typical meteorological data of Cairo, Egypt. In Configuration-I, adsorption system is driven by solar collectors and vapor compression system is electrically powered. In Configuration-II, supplementary photovoltaic panels are used to power the vapor compression cycle, resulting in a net-zero electricity consumption scheme. For prolonged operation, Configuration-III is presented with an additional cold storage tank between adsorption and compression subsystems. Silica/gel water is utilized as a working pair in the adsorption cycle, while R410A is employed for the vapor compression system. Mathematical modeling is formulated using the MATLAB/Simulink platform and validated against experimental data from the most relevant literature. For Configuration-I, theoretical results demonstrate that the electricity consumption reduces in June from 22.37 kWh to 5.9 kWh by increasing the size ratio between the adsorption and the compression systems from 0.867 to 1.333. Configuration-I can substantially alleviate the electricity consumption by 62.5% compared to the conventional vapor compression system. It is also found that Configuration-II can save electrical energy consumption as high as 2897 kWh/year. Although Configuration-III experiences annual energy savings of 47% compared with Configuration-I that achieves 64%, it operates for prolonged durations as a redeeming feature. Moreover, economic analysis is conducted for the three examined configurations, revealing that Configuration-II is economically viable with a payback period of 9.65 years. These findings could spur designers and stakeholders into utilizing new hybrid cooling systems in preference to the predominant compression cooling systems.
The influence of thermal energy storage (TEGS) of coupling new hybrid system of two phase change materials (PCMs) with air conditioning (A/C) unit on its cooling and heating performance in summer and winter, respectively is investigated. PCM RT 10 HC (PCM10HC) of 10-12°C phase change temperature and PCM type SP 24E (PCM24E) of about 24-25°C phase change temperature suitable for working on winter and summer climate conditions, respectively are integrated as a hybrid system and coupled with the condenser/evaporator of the A/C unit. The performance of the A/C unit of this hybrid system is compared with the unit performance using only PCM24E system in summer and PCM10HC system in winter. The study is studied at two configurations of the hybrid PCMs system. The studied physical systems are modeled by a complete mathematical model that is numerically solved by utilizing ANSYS-Fluent software. The solution numerically is validated by using an experimental setup which shows the high accuracy of the numerical solution. The findings based on the stated design conditions of Egypt demonstrate that the time of complete charging and discharging procedures is nearly the same for hybrid and single PCMs systems. The maximum increase of the A/C unit COP is about 88% for the hybrid system in summer while it is nearly 22% in winter. The percentage increase of the saving power for the single system, the hybrid system is about 6.85%, and 6.5%, respectively in summer and 3.9% and 2.8% in winter, respectively compared to A/C without PCM units. Increasing the distance between the PCMs’ plates impacts negatively on the exit air temperature from PCMs plates and the saving power. The results demonstrate that the hybrid system has nearly the same merits on the A/C working as the single systems plus it can work during the hot and cold climate conditions.
A high-pressure lift often triggers an increased power input to the vapor compression systems. The increased power consumption becomes a bottleneck in R-744 refrigeration systems for freezing and refrigeration applications. Meanwhile, phase change materials (PCM) offer operation flexibility in the form of the compressor run-time from the energy storage potential. In this article, the energy-saving potential of the PCMs on a cascade refrigeration system using CO2 is investigated focusing on the impacts of charge amounts and the thermal resistance of the PCM. The validated dynamic model in Simscape™/MATLAB for an R-744 vapor compression system is adopted for a cascade refrigeration system together with the validated PCM model. In the studied system, the PCM is installed in the storage compartment as a thermal buffer. The comprehensive model employed an acausal, object-oriented, and equation-based paradigm adopting detailed heat transfer characteristics. The effect of PCM on the compressor running time was investigated under the cyclic steady-state operating conditions. The results showed that the compressor “On-time” ratio decreases when using the PCM; subsequently, the power reduction. The system consumes about 6.76 kWh (without PCM) and 5.93 kWh with PCM; thus, the power consumption decreases by 12.3%. The threshold PCM charge ratio is observed to be 1. Increasing the PCM charge value above this threshold does not trigger a significant decrease in power reduction. The increase in the overall thermal resistance of PCM has a negative impact on the “On-time” ratio and power consumption. The benefit of PCM is insignificant for thermal resistance above 0.02 K W⁻¹. Despite the shortcomings of several assumptions involved, the present results clearly highlight the positive impacts of the PCM in terms of power savings for low-temperature refrigeration applications using R-744.
Phase change materials (PCMs) based thermal energy storage (TES) has proved to have great potential in various energy-related applications. The high energy storage density enables TES to eliminate the imbalance between energy supply and demand. With the fast-rising demand for cold energy, cold thermal energy storage is becoming very appealing. In this paper, a review of TES for cold energy storage consisting of various liquid-solid low-temperature PCMs has been carried out. The classification of the PCMs is briefly introduced. Recent approaches to optimizing the properties of PCMs, particularly to remedy the poor thermal conductivity, leakage of liquid PCMs and the high degree of super-cooling, which limits the cold applications of TES, have also been reviewed. Methods for increasing the thermal performance including using composite PCMs and solid mesh are compared. Both modelling and experimental research on cold energy storage devices have been examined. The current cold energy storage applications including air conditioning, free cooling, etc. have been summarised. Compared with previous reviews, this work emphasises the cold energy storage applications instead of the materials aspects. The main challenges and approaches to cold thermal energy storage from the perspective of the engineering applications have been identified. Recommendations for future low charging rates and device design methodology are proposed.
Phase Change Materials (PCMs) can absorb and release a high amount of energy, and therefore, can be used for shifting electricity demand in some household appliances. Indeed, the use of PCMs in a cabinet refrigerator leads to increase its OFF time and flexibility and moves the energy consumption to other periods for a reduction of the peak energy demand. The higher flexibility of the refrigerator with PCM can be exploited to reduce its running cost considering that many countries adopted Time-of-Use (TOU) tariffs, in which the electricity cost is based on the time of energy use over a day and a week. Hence, this work proposes an algorithm based on Simulated Annealing (SA) method to identify the optimal working scheduling of a refrigerator with PCM to reduce its running costs. Experimental results have been used as inputs for the algorithm, and nine 2-TOU and three 3-TOU electricity tariffs from different European countries have been selected to test the methodology. The possibility to achieve running cost savings for various case studies has been proven. Furthermore, higher is the difference between the peak and off-peak electricity cost; more significant is the economic benefits reached by the proposed method.
This paper presents the state-of-the-art of the integration of adsorption chillers into different configurations of combined cooling, heating, and power (CCHP) systems. Adsorption chillers, as a thermally-activated cooling system, provide a great solution to the utilization of low-temperature waste heat, thus help to increase the efficiency of the existing power generating systems, and to reduce the greenhouse gases emissions including the chlorofluorocarbons (CFC) that is used in traditional electric-powered chillers. In this study, a brief introduction to CCHP systems and the thermally-driven cooling systems is presented, and the working scheme of the adsorption cooling cycle is illustrated. The paper also focuses on the CCHP systems integrated with adsorption chillers that are driven by solar thermal energy via different solar collectors. Furthermore, multigeneration systems driven by internal combustion engines, gas turbines and fuel cells are highlighted. Finally, the integration of adsorption chillers in hybrid cooling systems with Organic Rankine Cycles (ORC) is also presented.
The efficient utilization of renewable energy sources should rely on the exploitation of a mix of thermal and electric energy rather than relying on a single energy source. One way to apply this shared generation concept to space heating/cooling and refrigeration in both residential and industrial sector is through hybrid sorption-compression chillers. However, the experience on these systems is still limited and therefore their design and optimization require some efforts. Starting from the experimental experience on the testing of different hybrid cascade chillers, and integrating the measurement with a dynamic model, some considerations on the sizing, design and optimization of hybrid thermal-electric chillers are reported. In particular, design conditions of pre-commercial or commercial systems are evaluated and optimization at different levels is proposed, i.e. on the core components (through the proper design of relative capacities of the units in the cascade and through proper selection of the refrigerant), on the auxiliaries, to reduce their electricity consumption, and on the overall management of the hybrid chiller. Results demonstrated that the higher is the operating temperature lift between evaporator and condenser the higher are the achievable energy savings of a cascade chiller.
A study on the thermal energy storage (TES) of phase change materials (PCM) coupled with the condenser of air conditioning unit (ACU) is carried out for PCM 24 E, PCM 26 E, and PCM 29 Eu. This coupling technique is based on using the cold energy storage (CES) of the PCM by the cold ambient air at night to cool the ACU condenser at daytime. The study is performed during charging and discharging of the CES at various inlet ambient air temperatures and velocities to the PCMs plates at day and night times. The mathematical model of the physical model is solved numerically by using ANSYS-Fluent software. The findings reveal that during the discharging process, the exit air temperature from the PCM plates is reduced with increasing the inlet air temperature and velocity. The coefficient of performant (COP) of the ACU coupled with the PCM is decreased with time. It starts by a higher value for low phase change temperature (PCT) than high PCT and after a period this trend is reversed. The time required to charge completely the PCM with CES for PCM 26 E is smaller than other studied PCMs at the same temperature difference between the PCT and the ambient. Decreasing the PCM plate width has the advantage of reducing the solidification time but it reduces the saving power by about 10.5%. The saving power due to using PCM rises with decreasing the ambient temperature and inlet air velocity. It is about 8.25, 8.4, and 8.95% for PCM 24 E, PCM 26 E, and PCM 29 Eu, respectively at ambient temperature 35 °C and air velocity 0.96 m/s.
Sustainable refrigeration systems are of great importance to reduce greenhouse gas emissions. In particular, CO2 vapour compression cycles are very promising due to their environmentally friendly, natural refrigerant. However, a major challenge for implementing CO2 cycles is the low efficiency at high ambient temperatures resulting from high exergy losses in transcritical operation. To increase the efficiency, we present a hybrid system concept integrating an adsorption chiller into the CO2 cycle. The adsorption chiller employs the natural refrigerant water and is driven by waste heat from the CO2 cycle. The additional cooling generated by the adsorption chiller is integrated into the CO2 cycle to increase the efficiency of the overall hybrid system. Compared to a stand-alone CO2 cycle, we show by dynamic modelling and optimisation that the hybrid system leads to annual energy savings of 22% for a warm climate in Athens and of 16% for a moderate climate in Cologne. The results highlight the high potential of the hybrid system concept to efficiently provide refrigeration using environmentally friendly refrigerants.
In this paper, a Phase Change Material (PCM) has been incorporated within the cabinet of a refrigerator, attached to the bare tube evaporator placed below the racks, with the aim of analysing the variation of temperatures and compressor operation, among others. The effect of different control settings (hysteresis) on the performance of such a system, equipped with tap water as PCM, is investigated. Furthermore, the impact of the variation of the ambient temperature and the product mass is highlighted. Two novel parameters are introduced: the first one to estimate the utilisation of the PCM during the cyclic operations of the refrigerator, and the second one is used to evaluate the fluctuation of the product temperature within the cabinet. Experimental results show that the introduction of the PCM has led to a noticeable reduction of the temperature gradient within the cabinet and the fluctuations of product temperature ensuring better conservation conditions, and to extend the OFF time of the compressor. The tests also show that with PCM, hysteresis has lower impact on the fluctuation of the product temperature, ON-time ratio and energy consumption of the refrigerator than without it. On the contrary, the product temperature distribution is more affected by the hysteresis with PCM than without, leading to a better uniformity with higher hysteresis.
Waste heat is a major source of recoverable loss in societal energy use, offering significant potential for reduction in greenhouse gas emissions. A number of studies have been carried out to determine the size of the available resource but have been limited in scope or confined to the status quo. This work reports a method to quantify future global waste heat emissions from the Power Generation, Industry, Transport, and Buildings sectors, and
investigates their environmental effects. Four projected energy landscapes (World Energy Outlook 2016: 1. Current Policies; 2. New Policies; 3. 450-scenario. 4. 100% renewable energy penetration) were simulated to assess the amount of waste heat produced in different sub-sectors in the year 2030. The impact of CO2 radiative forcing and various technological shifts are reported. Total waste heat emissions are found to account for
23.0–53.0% of global input energy depending on year and scenario, with a range of theoretical and economic recovery potentials of 6–12% and 6–9% respectively. Further insight is gained into the waste heat landscape through analysis of temperature and sectoral distributions, and identification of hotspots for targeted waste heat recovery. When considering emissions from 2014 to 2030, the integrated radiative forcing of CO2 is found to be
13 times greater than that of waste heat, primarily attributable to the former’s cumulative nature. Full recovery of the theoretical potential is found to lead to a 10–12% reduction in the combined forcing of CO2 and waste heat over this period, mainly due to a reduction in CO2 emissions. Under a conservative carbon tax, this reduction is estimated to offer potential economic savings of $20-77bn/year. A 10% increase in the penetration of solar/
wind/tidal hydroelectric power and electric vehicles are found to decrease global waste heat losses in liquid and gaseous streams by 5% and 0.7–2.0%, respectively; retrofitting of Carbon Capture and Storage to power plants decreases CO2 radiative forcing, outweighing the increase in thermal radiative forcing from additional waste heat streams.
Researchers, practitioners, instructors, and students all welcomed the first edition of Heat Exchangers: Selection, Rating, and Thermal Design for gathering into one place the essence of the information they need-information formerly scattered throughout the literature. While retaining the basic objectives and popular features of the bestselling first edition, the second edition incorporates significant improvements and modifications. New in the Second Edition: • Introductory material on heat transfer enhancement • An application of the Bell-Delaware method • New correlation for calculating heat transfer and friction coefficients for chevron-type plates • Revision of many of the solved examples and the addition of several new ones The authors take a systematic approach to the subject of heat exchanger design, focusing on the fundamentals, selection, thermohydraulic design, design processes, and the rating and operational challenges of heat exchangers. It introduces thermal design by describing various types of single-phase and two-phase flow heat exchangers and their applications and demonstrates thermal design and rating processes through worked examples, exercises, and student design projects. Much of the text is devoted to describing and exemplifying double-pipe, shell-and-tube, compact, gasketed-plate heat exchanger types, condensers, and evaporators.
This paper presents a study on a new technique of using thermal energy storage of phase change material system with conventional air-conditioning unit to increase its cooling performance. The technique is based on integrating plates of phase change material with the condenser of the air-conditioning unit. The phase change material plates use its cold storage energy during the night time to increase the cooling performance of the unit during the daytime. The air is used to transfer the cold storage energy from the phase change material plates to the air-conditioning unit during the daytime. The study is performed during charging the phase change material with cold storage energy at night and discharging this energy to the air-conditioning unit at daytime. A theoretical transient model for the phase change material with air heat exchanger is constructed and a numerical solution of the theoretical model is presented. The numerical solution of the theoretical model is validated with an experimental work. The effect of the phase change material plates configurations and the inlet velocity and temperature of the air inlet to the phase change material plates on the charging and discharging process is carried out. Also, the effect of these parameters on the air-conditioning unit performance is presented. The results show that the longer and thinner phase change material plates configuration has the lower charging and discharging time. The discharging time and the outlet cold air temperature from the phase change material plates are decreased with increasing inlet air velocity and temperature. The charging time is decreased with decreasing inlet air temperature and rising inlet velocity. The maximum increase of the coefficient of performance of the air-conditioning unit with phase change material for the different configurations compared to the conventional one for inlet air temperature 35 °C, is 14%, 13% and 12% for inlet air velocity 0.96 m/s, 1.2 m/s and 1.44 m/s respectively. The discharging and charging time and the outlet cold air temperature from the phase change material plates are decreased with increasing inlet air velocity and temperature respectively. Also, at inlet air temperature 45 °C, and velocity 1.44 m/s, the maximum useful cooling power per kg of the phase change material is 46, 50, 54, 55, and 67 W for the configurations 2, 5, 4, 1 and 3 respectively. The results illustrate that, at air inlet velocity 0.96 m/s, the maximum percentage of the saved power per ton refrigeration for each kg phase change material with respect to conventional AC unit is about 11.6%, 6.7% and 5.4% for inlet air temperature 45 °C, 40 °C and 35 °C respectively.
This paper presents a model for a variable-speed liquid chiller integrating a compressor model based on Buckingham π theorem to accurately predict the system performance when R134a is replaced with R1234yf, using a wide range of data obtained from an experimental setup. Relevant variables such as temperature, pressure, mass and volumetric flow rates, compressor power consumption and rotation speed were measured at several positions along the refrigeration and secondary circuits and were used to validate the developed model. Model results show that cooling capacity and power consumption predicted values are in good agreement with experimental data, within ±5%, being slightly higher for the deviation obtained for R134a than for R1234yf. Moreover, model results indicate that R1234yf has a reduction of coefficient of performance (COP) compared with R134a (between 2 and 11.3%), and that R1234yf COP reduction is diminished at intermediate volumetric flow rate and higher inlet temperature for the evaporator secondary fluid, respectively. On the other hand, an environmental analysis based on TEWI (total equivalent warming impact) method showed that direct emissions are almost negligible for R1234yf. However, there are no environmental benefits in terms of indirect greenhouse gas emissions using R1234yf without system modifications (as for instance the addition of internal heat exchanger or R1234yf new design components), which are required to reduce the liquid chiller climate change contribution using it as low GWP alternative in comparison with the typically used R134a refrigerant.
An experimental work on using a new technique of thermal energy storage system with conventional air conditioning (AC) unit to raise its performance is presented. The technique is based on integrating plates of phase change material (PCM) with the condenser of the AC unit. The PCM plates use their cold storage energy during the night to increase the cooling performance of the AC unit during the next daytime. An experimental test rig for the PCM thermal storage plates is constructed in two configurations; horizontal and vertical plates. The experimental study is performed during the discharging of the charged cold storage energy at night to the AC unit at day. The effect of the PCM plates configurations and the velocity and temperature of the air inlet to the PCM plates on the discharging process and AC unit performance is presented. The results show that the coefficient of performance (COP) of the AC unit with PCM plates is greater than its COP without using PCM plates. At the initial period of the process, the outlet air temperature from the vertical PCM plates is smaller than that of the horizontal plates and after a certain period, the situation is reversed. Using PCM plates heat exchanger decreases the condenser pressure and increasing the evaporator cooling capacity. At inlet air velocity and temperature 0.96 m/s and 45 °C, using vertical and horizontal PCM plates decreases the consumed power of the AC unit by about 9.8% and 11.2%, respectively compared with AC unit without PCM plates.
In this paper the experimental testing of a cascade chiller composed of an adsorption unit and a vapour compression unit is reported. The operation of the cascade under realistic operating conditions, differing for the temperature of the heat source available and the environmental temperature is analysed. A comparison was made between the application of the cascade and a vapour compression chiller only for air conditioning applications. According to the heat source temperatures, an increase in the electric COP of the system ranging from 25% to 50% was measured, with a maximum value of 8. An optimization of the system was subsequently proposed, by evaluating different adsorbent materials and refrigerants through the use of thermodynamic models. The theoretical study revealed that a performance up to 110% higher with respect to traditional chillers could be obtained if the cascade was used in refrigeration applications.
A household refrigerator designed to work with R134a was used as an investigation unit to assess its transient startup and cyclic characteristics using ternary hydrocarbon mixture. Twenty-five combinations of refrigerant mass (30, 40, 50, 60 and 70g) and capillary tube length (4, 4.5, 5, 5.5 and 6m) are tested under severe tropical environment using a mixture of propane: isobutene: n-butane of 60:26.6:13.4% by mass. Also, typical variations of compressor, condenser and evaporator temperatures during transient and cyclic operations are considered. The energy losses during off-time are addressed by comparing refrigerator power during cyclic and continuous operation. The results demonstrate that while 15 out of 25 tested combinations satisfy the required air freezer and cabinet temperatures and achieve reasonable startup transient characteristics, only 5 combinations work satisfactorily under cyclic operation. The most appropriate combination of charge and capillary tube length is identified to be 70g and 5.5m. This combination consumes the lowest energy during permanent cyclic operation and achieves reasonable cooling rate, pull-down time and startup energy. In comparison with R134a, the energy applied to this combination may save about 306.6kWh annually for each refrigerator that would result in 36.8TWh on the world scale.
This paper presents an in-depth numerical and thermodynamic study of a two-stage, 2-bed silica gel/water adsorption system for simultaneous generation of cooling power and potable water. The system is air cooled where the ambient temperature remains constant at 36 °C. The first part of this paper investigates the effect of cycle time, chilled water inlet and heat source temperature on system performance viz. specific cooling capacity (SCC), specific daily water production (SDWP) and coefficient of performance (COP). A significant outcome of this study is to show that decrease in heat source temperature not only reduces the specific throughput but also increases the optimum cycle time, whereas COP is relatively insensitive to such alterations. The second part of this paper discusses the estimation of the minimum desorption temperature from the simulated system throughput results as well as from fundamental thermodynamic analysis of a two-stage adsorption cycle. This thermodynamic analysis provides a theoretical limit for minimum desorption temperature and optimal inter-stage pressure for a two-stage adsorption cycle.
Growing awareness of the potential environmental impacts of various refrigerants has led to the phasedown of hydrofluorocarbon (HFC) refrigerants and to initiatives replacing HFCs with hydrocarbons or other environmentally friendlier fluids. This study evaluated the performance of R290 (propane) and R600a (isobutane) as substitutes for R134a (a HFC) for heat pump water heating (HPWH). A component-based model (calibrated against the experimental data) was used to predict the performance of the HPWH system. Key performance parameters such as unified energy factor, first hour rating, condenser discharge temperature, thermal stratification in the water tank, and total refrigerant charge were investigated. Analysis results suggest that both alternative refrigerants could provide comparable system performance to that of the baseline system containing R134a, with one caveat. As a drop-in alternative, R290 was found to be a better substitute for R134a, whereas R600a is expected to provide similar performance if the compressor size is increased to provide similar heating capacity. Significant reductions in system charge and lower condenser discharge temperatures were identified as additional benefits.
This paper presents a novel compression-adsorption hybrid that symbiotically combines adsorption and CO2 compression cooling devices. The seemingly low efficiency of each cycle individually is overcome by an amalgamation with the other. Hence, both heat and water vapour refrigerant mass are recovered for continuous cooling and desalination. Two different configurations are presented. The first configuration deals with a two-stage heat recovery system. At the first stage, heat is recovered from the compressed carbon dioxide to drive the adsorption device. The second stage heat recovery system internally exchanges heat between the low pressure and high pressure refrigerants of the CO2 cycle. The second configuration is proposed with an additional third-stage heat recovery from the gas cooler to the high pressure evaporator of the adsorption cycle. The water vapour mass is recovered from bed-to-bed adsorption at relatively higher pressure. A detailed thermodynamic framework is presented to simulate the performances in terms of COP (coefficient of performance), SCP (specific cooling power), SDWP (specific daily water production), PR (performance ratio) and OCR (overall conversion ratio). It is found that the overall COP is improved by more than 60% as compared to the conventional CO2 cycle, and in addition, the system generates 12.7 m³ of desalinated water per tonne of silica gel per day as extra benefits. Furthermore, both the heat and mass recoveries improve the overall conversion ratio, which is almost double as compared to the conventional CO2 cycle.
This study presents a theoretical investigation into integration of phase change materials (PCMs) with an adsorption cooling system in order to provide 24-hour air conditioning. A latent heat storage unit containing PCM is used to store solar energy during the daytime, and at nighttime the conserved thermal energy and an auxiliary heater drive the adsorption chiller. The system adopts a cooling channel to reduce the air temperature. The air flow to the channel is provided by use of fans and at different fresh air ratios (FR). Room temperature and the room's maximum cooling demand for which thermal comfort can be achieved are estimated. In addition, the effects of different parameters on room temperature and solar fraction are studied. It is indicated that an optimum ACH value exists for which the room temperature is the lowest. Also, rise of ACH and FR decrease solar fraction and increase auxiliary energy consumption. It is found that when ACH = 4 and FR = 20%, daily solar fraction is 0.76 and 217 MJ of auxiliary energy is required during the 24 hours. Under this condition, thermal comfort is achieved for a maximum cooling demand of 4000 W during the 24 hours.
This study numerically investigates the influence of integration of a phase change material (PCM) slab inside a vertical beverage cooler (VBC) on the energy consumption, the thermal stability and flow characteristics of air inside the cooler. The PCM, water, slab is placed on the rear side of the flat plate roll bond evaporator with five different thicknesses, such as 2, 4, 6, 8, and 10 mm. In the current work, transient numerical analyses are performed with ANSYS-FLUENT software for an empty cooler. To simulate the on/off controller of the cooling system a dedicated user-defined-function (UDF) is implemented in the software. Unlike the counterparts in the recent literature, instead of reducing the problem into a 1D or 2D lumped models a three-dimensional cooler domain is simulated in a commercial CFD solver. The predictions are compared with the experimental measurement for the cooler without PCM regarding the transient variations of the mean temperatures of evaporator surface and the indoor air. Consequently, the parametric set of analyses deduced that the PCM integration into the cooler enhances the cooling performance of the VBC by prolonging compressor off duration. Moreover, during the compressor off time, PCM preserves the air temperature inside the refrigerated space in the desired range by limiting the sudden temperature increments.
This work presents a performance evaluation of a vapor injection refrigeration system using a mixture refrigerant R290/R600a, through steady-state simulations used to accomplish a parametric analysis considering the influence of the refrigerant composition over the following parameters: COP; compressor power; refrigerant mass flow rate; refrigerant temperature glide; mass flow ratio between vapor and feed streams in the flash tank; liquid and vapor composition of flash tank outlet streams and compression ratio. Two cases, denominated A and B, considering different fixed temperatures at the refrigeration system were studied and their performances were compared with the one of a basic vapor compression cycle. A maximum COP was obtained for a mixture containing 40 wt% of R290. COP of vapor injection refrigeration cycle is 16-32% greater than the one of a vapor compression cycle, depending on the composition of the mixture refrigerant and pressure drop at the cycle upper-stage expansion valve. © 2016 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.
This paper is the second part of a study on the use of adsorption refrigeration cycles driven by waste heat of near-ambient temperature. Experiments were conducted with several heat transfer fluid operating temperatures (hot, cooling, and chilled water), flow rates, and adsorption-desorption cycle times, and good qualitative agreement was obtained with the simulated results. Both experiments and simulation showed that the silica gel-water adsorption cycle is well suited to near-environmental-temperature heat sources and small regenerating temperature lifts, which help reduce the heat losses intrinsic to batched cycle operation. The chiller was operational with a hot water inlet temperature (Thot in) of 50°C (122°F), and the highest experimental values of the coefficient of performance (COP) (more than 0.4) were obtained with Thot in = 50°C (122°F) in combination with cooling water at 20°C (68°F).
Efforts to increase energy efficiency of refrigerators shall directly reduce energy consumption in residential buildings. Incorporating Phase Change Materials (PCM) is a new approach to improve the performance of refrigerators. In this study, we have tested four different PCMs in two different refrigerator models. Compressor on/off time was optimized and better energy efficiency was achieved. Increasing condenser surface area by 20% enhanced the PCM effect. The use of only 0.95 kg of PCM has resulted in a 9.4% energy saving. Economic analyses show that using PCMs in household refrigerators is clearly a cost effective method that saves energy and reduces harmful emissions.
Low temperature sensitive products transport and storage is an issue worldwide due to changes of the lifestyle population increase. Thermal energy storage (TES) is nowadays one of the most feasible solutions in facing the challenge of achieving energy savings. Many researchers have investigated energy efficiency of different cold units by applying TES systems using phase change materials (PCM). This paper provides an overview of the existing Spanish and European potential energy savings and CO2 mitigation by incorporating TES systems to cold storage and transportation systems. Data on energy savings were compiled from different case studies. Results depend on the scenarios studied and the extent of TES systems implementation; in the case of Europe for instance, yearly CO2 emissions may be cut down between 5% and 22% in reference to 2008 CO2 emissions from cold production considering that the proposed implementation of PCM TES in the case studies found in the literature is done.
This paper presents the theoretical analysis of the performance of solar powered combined adsorption refrigeration cycles that has been designed for Singapore and Malaysia and similar tropical regions using evacuated tube solar collectors. This novel cycle amalgamates the activated carbon (AC)-R507A as the bottoming cycle and activated carbon-R134a cycle as the topping cycle and deliver refrigeration load as low as −10 °C at the bottoming cycle. A simulation program has been developed for modeling and performance evaluation for the solar driven combined adsorption refrigeration cycle using the meteorological data of Singapore and Malaysia. The results show that the combined cycle is in phase with the weather. The optimum cooling capacity, coefficient of performance (COP) and chiller efficiency are calculated in terms of cycle time, switching time, regeneration and brine inlet temperatures.
Experimental results are presented of the refrigerant mass charge distribution in a steadily cycling domestic refrigerator. In detail it is shown how the charge is displaced at compressor start-up and shut-down. At start-up it was found that the charge was temporarily displaced towards the condenser before returning to a steady state distribution in the latter part of the on-period. As a result, initially the evaporator was starved with a lowered evaporation temperature and a peak 10 °C superheat. The superheat disappeared within 3 min as the evaporator was gradually refilled with refrigerant. At shut-down the pressure equalised within 3 min as refrigerant was pushed into the evaporator from the condenser. The losses due to charge displacements were estimated to 11% (capacity) and 9% (efficiency). Possible ways to reduce the losses are discussed.
This article presents a transient distributed-parameter model for a two-bed, silica gel–water adsorption chiller. Compared with our previous lumped-parameter model, we found better agreement between our model prediction and experimental data. We discussed the important effect of heat recovery and the effect of extra system piping on the system performance. Time constants of sensors were also considered. We found that the chiller was able to maintain its cooling capacity over a fairly broad range of cycle times and the previous lumped-parameter model tended to under-predict the cooling capacity at long cycle times.
American Society of Heating, Refrigeration and Air Conditioning Engineers Inc., ASHRAE Handbook: Refrigeration
ASHRAE, 2014. American Society of Heating, Refrigeration and Air Conditioning Engineers
Inc., ASHRAE Handbook: Refrigeration.