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The present research aims to achieve a shape-stable, and leakage-proof material for thermal energy storage (TES). The leakage analysis of 20 wt.% SiO2@Cu PCM shows 0.05%, as a result, more testing is conducted to assess its morphology, structure, and thermal properties. TGA and DSC studies demonstrated that the latent heat and thermal degradation rate (TDR) has been delayed, with a significant decrease in latent heat of roughly 8.7% compared to pure paraffin. Laser Flash Method (LFA) results revealed that the thermal conductivity (TC) of the PCM composite significantly increased 4.84 times than the paraffin. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the melting characteristics of a phase change material (PCM) in a latent heat storage system equipped with hemispherical and quarter-spherical fins. A vertical triple-pipe heat exchanger is used as the PCM-based heat storage unit to improve the melting performance compared with a double-pipe system. Furthermore, the fins are arranged in inline and staggered configurations to improve heat transfer performance. For the quarter-spherical fins, both upward and downward directions are examined. The results of the system equipped with novel fins are compared with those without fins. Moreover, a fin is added to the heat exchanger's base to compensate for the natural convection effect at the bottom of the heat exchanger. Considering similar fin volumes, the results show that the system equipped with four hemispherical fins on the side walls and an added fin on the bottom wall has the best performance compared with the other cases with hemispherical fins. The staggered arrangement of the fins results in a higher heat transfer rate. The downward quarter-spherical fins with a staggered configuration show the highest performance among all the studied cases. Compared with the case without fins, the heat storage rate improves by almost 78% (from 35.6 to 63.5 W), reducing the melting time by 45%. [ABSTRACT FROM AUTHOR]

Climate change is forcing action to reduce energy consumption and greenhouse gas emissions. An extremely important area of high-polluting energy consumption is material transport and, within this, the transport of chilled goods, including deep-frozen goods, is an important contributor. Phase change materials (PCMs) can have an important role in reducing energy consumption for the transport of chilled goods, but the current state of knowledge is not sufficient to bring the solution into popular use. This article includes a study of the effect of implementing microencapsulated PCM (mPCM) in polyurethane foam (PU) on the insulation performance of refrigerated trailer walls in low-temperature transport. In this research, mPCM was used, characterised by a phase-change heat in the range of 170–195 k J k g and a phase change temperature in the range from −10 °C to −9 °C. The studies performed show the potential of using mPCMs to improve the insulation performance of the walls of refrigerated trailers. Containing mPCM in the amount of 5.0% wt. placed throughout the entire volume of the wall can improve thermal conductivity of the wall for up to 15% in peak and 4.5% (0.2792 W m 2 K without mPCM and 0.2665 W m 2 K with mPCM) in the phase change temperature range. Out of the range of phase change temperatures, the thermal conductivity of the wall with mPCM is worse for 2.72% than in walls without PCM. Problems that need to be tackled were also identified, before the solution can be put into everyday use, i.e., finding the technology to increase the proportion of mPCMs relative to PU. [ABSTRACT FROM AUTHOR]

Thermal control is a critical functionality in space applications due to the narrow operation temperature range of the on-board systems, and, on the other hand, due to the harsh environment the spacecraft is subject to. Thermal control systems based on phase change materials have the main advantage that are passive and, if properly designed, are highly reliable and efficient. Some Phase Change Materials (PCMs) – paraffins – have other applications for spacecrafts, such as mechanical actuators, which convert temperature changes to mechanical work. In contrast to thermal control terrestrial applications, space applications have more constraints and must ensure compatibility with more systems. One of the most important constraints in space systems is the mass. The design and choice of thermal regulation systems often boils down to replacing heat dissipation radiators mass with lighter, PCM elements. The review is centered around the main application area of PCMs in space applications, discussing numerical and experimental studies on the design and multi-objective optimization of thermal control systems for spacecrafts. Other PCM applications in spacecraft technology are discussed such as micro-actuators, thermoelectric devices, propulsion systems and thermal protection for reentry vehicles. Not only PCM applications are discussed but also some specific issues which are highly important in the design and effective operation of PCM-based thermal control systems for spacecrafts. Thus, issues such as materials, performance enhancement, stability, compatibility and phase transition process under microgravity or hyper gravity were reviewed. • Phase change materials applications in space systems were reviewed. • Phase change materials applications other than heat storage were discussed. • Microgravity and hyper gravity effects on the phase transition process were discussed. • Thermal efficiency enhancement methods were reviewed. • Corrosion and stability issues were discussed. [ABSTRACT FROM AUTHOR]

This study investigated the impregnation of beech and thermally modified beech (TMB) with a ternary mixture of capric acid, palmitic acid, and stearic acid as a bio‐based phase change material (BPCM). Finite element method (FEM) was used to complement the experimental analysis by providing new insights into computational methods for simulating the behavior of BPCMs in untreated and TMB. The analyzed specimens namely beech and TMB were impregnated with BPCM; the TMB achieved 54% weight percentage gain (WPG) while untreated beech got 37%. Accordingly, a greater increase in the latent heat was obtained for TMB up to 90 J/g, while for untreated beech with BPCM up to 75 J/g. Impregnated specimens absorbed less moisture at relative humidity of air above 50%, likely caused by the high uptake and hydrophobic nature of the BPCM. The study highlights the research gap in performing mathematical simulations on wood samples with BPCM using material thermal properties derived from differential scanning calorimetry or T‐History analysis. It shows that the direct use of these values for simulations leads to unacceptable outputs that result in high errors. The root mean square error for untreated and TMB samples impregnated with BPCM was in the range from 1.06 to 3.1 while that for untreated samples was in the range from 0.57 to 0.87, indicating that the main challenge in simulating and characterizing the samples is due to the interaction of the phase change material with the wood structure. [ABSTRACT FROM AUTHOR]

This paper presents a review of the storage of solar thermal energy with phase‐change materials to minimize the gap between thermal energy supply and demand. Various types of systems are used to store solar thermal energy using phase‐change materials. The performance of latent heat storage is dependent on the shape and size of the fins, the orientation and design of the storage unit, and its position. The efficiency of a solar thermal collector integrated with phase change material depends on the inclination of the collector, the position of the phase change material, and its thermo‐physical properties. The study of the thermo‐physical properties of various phase‐change materials and their effects is the focus of this paper. [ABSTRACT FROM AUTHOR]

Latent heat storage (LHS) using phase change materials (PCMs) is expected for application to heat utilization at high‐temperature because it can provide a heat source of high density and constant temperature. Even among PCMs, metals/alloys are promising for high‐temperature operation. However, metals and alloys PCM are concerned about corrosion reactions with structural materials. As a result, micro‐encapsulated PCMs (MEPCMs) have been created in which the surface of alloy PCM is encased in a stable oxide coating. Since the surface of MEPCM is an oxide, the creation of structures with the function of LHS in a variety of shapes by combining MEPCM with sintering aids is also possible. In this study, composite PCMs were prepared by combining Al‐25 mass% Si MEPCM with fine α‐Al2O3 particles as a sintering aid. Consequently, PCM composites containing 70‐90 vol.% of the MEPCM and heat‐treated at 1200°C or 1300°C were successfully fabricated. In particular, a high heat storage density of 0.47 GJ m−3 was obtained under conditions containing 90 vol.% of the MEPCM and a heat treatment temperature of 1200°C, which is 1.6‐fold higher than that of existing sensible heat storage materials. Additionally, the composite PCM retained its shape and the latent heat capacity even after 300 cycles of cyclic testing. Thus, the high heat storage density and high durability of the composite PCM are expected to further promote the expansion of high‐temperature heat utilization in future studies. [ABSTRACT FROM AUTHOR]

The development of energy storage systems has become crucial to reduce negative environmental impacts and overcome the mismatch between the required and produced energy. Thermal energy storage systems (TESS) have become highly relevant, and one of the most promising TESS systems is the latent heat thermal energy storage system (LHTESS) based on phase change materials (PCMs). However, the low thermal conductivity and poor heat transfer capabilities of PCMs limit their performance. The use of metal foams as porous media in LHTESS can enhance the low thermal conductivity of PCM and exploit its high energy density. The study performs a simulation on a vertical shell and convergent tube geometry composed of metal foam filled with pure paraffin wax as the PCM considering external heat losses and using the Darcy-Forchheimer model and the enthalpy-porosity theory to analyze the thermal behavior of the system. The numerical results show that the combination of metal foam with PCM significantly improves heat transfer, resulting in a much faster phase change process and reduced melting time. The study can also be expanded further to simulate other types of metal foam and PCMs. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of using a phase change material (PCM)-based latent heat storage (LHS) integrated with an air-conditioning system. The study has filled the knowledge gap regarding the dependence of melting rate and operational time of the AC system on PCM volume. Additionally, the study has examined the influences of important parameters such as inlet velocity and Stefan number on melting rates, outlet temperature, and COP. The results have revealed that higher inlet air velocity and Stefan number have led to shorter melting duration. Specifically, an increase in velocity from 1.6 to 2.14 m/sec has reduced the time required for complete melting by 19.16% at a fixed Ste value and D value of 2. Further increasing the velocity to 2.67 m/sec has reduced the time by 31.59%. However, increasing the volume of the PCM has resulted in a longer melting duration, with the total melting time increasing from 3.35 to 7.11 h. Better COP values have been obtained for low-velocity cases. For all cases examined, the COP of the AC system with PCM has been superior to the COP without the PCM at any given time. Increasing inlet velocity and Ste raised the outlet temperature of the HEX, while PCM volume had little impact. The results have also indicated that lower inlet velocity is suitable for longer working periods and lower AC cooling loads, whereas higher inlet velocity is appropriate for shorter working periods and higher AC cooling loads. [ABSTRACT FROM AUTHOR]

This work focuses on the encapsulation of two organic phase change materials (PCMs), hexadecane and octadecane, through the formation of nanocapsules of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) obtained by oxidative polymerization in miniemulsion. The energy storage capacity of nanoparticles is studied by preparing polymer films on supporting substrates. The results indicate that the prepared systems can store and later release thermal energy in the form of latent heat efficiently, which is of vital importance to increase the efficiency of future thermoelectric devices. [ABSTRACT FROM AUTHOR]

The low ability of phase change material (PCM) to transfer thermal energy has created a serious challenge for the development of latent heat storage (LHTES) units. Embedding foam with high thermal conductivity material like copper has attracted significant attention. Besides, high porosity, lightweight, and easy usage are other important benefits of copper. However, its higher cost and decreasing effective volume of PCM led to the creation of amendments in the foam design. Employment of the foam in the form of fin or foam fin has emerged as an alternative method to benefit from the advantages of porous material and overcome its defects. In this study, various LHTES units with different numbers of foam fins have been simulated numerically and compared with pure PCM and fully foam PCM enclosures. Two practical boundary conditions including constant temperature and constant heat flux were examined for the designed systems. The obtained results demonstrated that foam fins have a remarkable effect on the thermal performance enhancement of LHTES under constant temperature boundary condition. For LHTES with six foam fins, 42% and 30% reductions in melting time were achieved for both types of boundary conditions including constant temperature and heat flux, respectively. At the beginning of charging process, a significant enhancement of input heat rate was proved for LHTES with 6 foam fins and fully foam up to 112% and 155%, respectively. In addition, the foam fins method provided some free volume of PCM to permit the falling out of natural convection of molten PCM. [ABSTRACT FROM AUTHOR]

This work presents the materials selection process, the design and the dimensioning process of a latent heat storage tank that works between a high temperature heat pump and an Organic Rankine Cycle unit. The selected heat storage material is the S117 Phase Change Material that has a melting point at 117°C matches the operational temperature of the system at approximately 120°C. The tank configuration is selected for optimised heat transfer process, resulted from practical experience of the project partners and it is described in details in the document. The simulation results from the Computational Fluid Dynamic study of the tank are also presented here. This work should be useful for engineers designing compact heat storage tanks for medium temperature applications. [ABSTRACT FROM AUTHOR]

Recently, solar thermal energy has been considered the main type of renewable energy used widely to provide heat energy and produce electrical power. Evacuated tube solar collectors (ETSCs) are used in various weather circumstances such as clear, cloudy, windy, hot, and cold weather, and their efficient system supplies latent heat storage fluid with higher temperature and lower heat energy loss compared to the flat-plate solar collectors (FPSCs). This review paper is considered an investigation on adding nanofluid particles to the evacuated tube solar collector-PCM, indicating future evacuated tube solar collector designs and predicting the suitable high- or low-temperature PCM for various types of applications. Also, three main types of ETSCs, heat pipe, Thermosyphon, and U-pipe, with their applications are reviewed, and the factors that influence the collector performance and efficiency are discussed. Moreover, the properties that affect the selection of the PCM and the usage of various types, sizes, and volumetric concentrations of nanofluid as a working fluid for each ETSC are investigated with their enhancements for each type. Lastly, this paper provides future ideas for using additive nanofluid materials as a working fluid to improve the performance and efficiency of ETSCs. [ABSTRACT FROM AUTHOR]

Strengthening the thermal response of Phase-Change Materials (PCMs) is an essential and active field of research with promising potential for advanced applications such as solar energy storage, building energy conservation, and thermal management in electronic devices. This article evaluates the efficacy of a new arc-shaped fin array in shell-and-tube heat storage systems to enhance the PCM response during the discharge mode. Different fin geometric parameters including the fin curvature angle, the fin spacing, and the nonuniform angle between fins in the top and bottom sections of the PCM domain were considered to identify the best-performing layout. The analysis shows that increasing the curvature of arc-shaped fins between 60° and 180° and increasing the fin spacing between 5 and 15 mm can significantly reduce solidifying time and improve heat recovery rates. Moreover, the arc-shaped fins are more efficient than conventional longitudinal (+-shaped) fins, which are commonly employed in thermal energy storage applications. Arc-shaped fins can also save discharge time by more than half and improve the rate of heat recovery by almost four times than that of+-shaped fins. The present findings suggest that arc-shaped fins represent a promising design for enhancing the heat-recovery aspects in PCM-based energy storage systems. [ABSTRACT FROM AUTHOR]

Thermal energy storage (TES) system is the most eminent storage method that aids in the power generation. Latent heat storage (LHS) is on the rapid mark‐up that fosters the TES with the utilization of the phase transition of a material to store the heat. Typically the phase change materials (PCM) are used in the LHS system to store the energy. During the material's phase transition, thermal energy is stored and released. Nevertheless, the low thermal conductivity of the PCM in the LHS is susceptible to deteriorate the charging and discharging of the thermal energy. Hence there is a necessity to enhance the thermal performance of the LHS system, on which various studies have been done. Therefore this paper aims in providing a review on the enhancements of the LHS system with improved heat transfer rate and heat transfer enhancement techniques in the PCM for better efficiency. A comprehensive review on the LHS system component is provided to make an emphasis on the heat transfer enhancement rate and storage time. Various characterizations and categories of the PCM are provided to intensify the outcomes of the review as PCMs are most viable materials for storing thermal energy. In addition the recent researches on the integration of PCM with other materials are also discussed that help in the improvements of the thermal conductivity of the PCM. The selection parameters of the PCM materials are also discussed in brief to avoid the poor performance of the PCMs. The heat transfer analysis methods are analyzed to improve the efficiency and reduce the heat loss. Finally, advancements in the future trends for the enhancement of heat transfer is provided. [ABSTRACT FROM AUTHOR]

Microencapsulated phase change materials（MePCMs） with polyaniline（PANI） as shell material are a kind of important multifunctional MePCMs. In order to broaden the source of functionalized MePCMs with PANI shell, in this work, tetradecanol（TD） was selected as core material and a series of TD@PANI MePCMs were prepared via a simple surface polymerization of aniline in the TE/water suspension. The effects of emulsifiers and core shell mass ratio on the properties of the prepared MePCMs were investigated. The results showed that the addition of emulsifier was unfavorable to the formation of TD@PANI MePCMs. The encapsulation ratio and spherical regularity of the obtained MePCMs prepared in the reaction system without emulsifier were increased first and then decreased with the increase of the core shell mass ratio, and the best result was obtained when the core shell mass ratio was 4.8∶5.2. The onset phase change temperature of the MePCM prepared under optimal condition was 32.44 ℃ with a phase change enthalpy of 102.3 J/g and a encapsulation ratio of 46.4%. Besides, the prepared MePCM possesses good thermal stability. In addition, the chemical properties and crystal structure of the tetradecanol core material did not change after it being microencapsulated by PANI. The results of this study can build a solid foundation for the development of multifunctional MePCMs with PANI shell. [ABSTRACT FROM AUTHOR]

Multiple factors govern the thermo-hydraulic behaviour of latent heat storage devices. The correlation among these factors varies from case to case. In this work, a concentric tube in tube latent heat storage system is numerically modelled. A fixed grid enthalpy porosity approach is adopted to account for phase change. The grid independence is achieved by testing mesh size, time step, and maximum iterations per time step. The computational approach is validated against the experimental data. It has been found that at the higher Rayleigh numbers, the bottom charging will result in faster melting compared to top charging. So, bottom charging is analysed in this work. Non-dimensional parameters, viz Rayleigh number (3.04x105 to 65.75 x105), Stefan number (0.2 to 1), Reynolds number (600 to 3000), and L/D ratio (2 to 15), are varied in the respective ranges mentioned in parenthesis. Stefan number is found to have a major influence on the Melt Fraction and Melting time, compared to Rayleigh number and Reynolds number. Correlations are developed for quantifying the melt fraction as MF = C.StA.RaB.ReC.FoD.(L/D)-F. Also, for the dimensionless melting time, correlation is proposed in the form Focm = G.(L/D)H.St-J.Ra-K.Re-L. [ABSTRACT FROM AUTHOR]

Nano-sized high conductive particles are extensively used in many engineering applications to achieve enhanced thermal performance. Paraffin wax is regarded as the most promising phase change material (PCM) for energy storage applications. However, the low thermal conductivity of paraffin poses a challenge which decreases the performance of storage system. In this work, composite PCMs consisting of paraffin and copper (Cu) nanoparticles were synthesized at different mass percentages (0%, 0.5%, 1%, 2% and 3%) and the thermo-physical properties were examined experimentally. The field emission scanning electron microscope (FESEM) results showed that the dispersion of nanoparticles in the PCM is homogeneous. The differential scanning calorimeter reports revealed that the effect of nanoparticle addition on phase change temperature is insignificant. On the other hand, reduction in latent heat is observed. The addition of nanoparticles is found to be critical in prolonging the thermal degradation of the storage medium which ensures the thermal and chemical stability of nano-Cu–paraffin composites. Moreover, the thermal conductivity of solid PCM is enhanced by 7%, 14%, 24% and 30.5% with the nanoparticle loading of 0.5%, 1%, 2% and 3%, respectively. In case of liquid PCM, the enhancement is found to be 8%, 15%, 28% and 31.5% with mass fraction of 0.5%, 1%, 2% and 3%, respectively. Altogether, the obtained results have revealed that the enhanced properties make nano-Cu–paraffin composite PCM as right candidate for solar thermal energy storage. [ABSTRACT FROM AUTHOR]

Thermal control methods based on phase change materials have a wide range of applications, from thermal management to latent heat storage for renewable energy systems, with intermittent availability. Organic PCMs have some advantages over inorganics; however, their major drawback is flammability. In critical applications, such as buildings, electric vehicles, and aerospace applications, flammability is an issue that must be addressed in order to comply with safety standards. This review paper covers current studies assessing the PCM response to fire or excessive temperature, methods for ensuring flame retardancy, and their impact on the PCMs key characteristics: phase transition temperature range, latent heat, heat transfer rate, and compatibility with other system materials. A special focus is set on the preparation methods and the effectiveness of the flame-retardance achievement method. Some research gaps and further research directions are identified and discussed. [ABSTRACT FROM AUTHOR]

Electric vehicles battery systems (EVBS) are subject to complex charging/discharging processes that produce various amount of stress and cause significant temperature fluctuations. Due to the variable heat generation regimes, latent heat storage systems that can absorb significant amounts of thermal energy with little temperature variation are an interesting thermal management solution. A major drawback of organic phase change materials is their low thermal conductivity, which limits the material charging/discharging capacity. This review paper covers recent studies on thermal performance enhancement of PCM thermal management for electric vehicles batteries. A special focus is placed on the constraints related to electric vehicles battery systems, such as mass/volume minimization, integration with other battery thermal management systems, operational temperature range, adaptability to extreme regimes and modulation of the melting/solidification behavior. The main research outcomes are as follows: quantitative/comparative assessment of common enhancement technique in terms of performance; approaches to deal with special constraints related to EVBS from the thermal control point of view. [ABSTRACT FROM AUTHOR]

The savings achieved as a result of energy efficiency studies are extremely important. As a matter of fact, the energy saved contributes in many ways, including effective use of resources, human health and environmental aspects. Therefore, the benefits of energy storage technologies to energy efficiency studies are significant. With the development of technology and changed needs, energy is demanded to be stored and used elsewhere and/or at another time. For this reason, studies are carried out by researchers on the storage of energy in various forms. The thermal energy storage method among energy storage technologies has been one of the research topics that have attracted attention in recent years in terms of reducing energy consumption amounts and costs. The new generation energy materials, called Phase Change Material (PCM), which enables the storage of latent thermal energy, are among the promising energy storage materials that can be used to achieve this goal. In this study, active and passive system applications based on PCMs were examined. For this purpose, the results obtained by researching the studies in the literature on this subject are presented in a systematic way. As a result of the examinations, it was seen that the studies generally focused on heat transfer and performance improvements due to the relatively low thermal conductivity of PCMs. [ABSTRACT FROM AUTHOR]

Considerable literature has studied different techniques to improve the thermal performance of latent heat thermal energy systems (LHTES) that utilize phase change materials (PCMs). This study aims to contribute to this growing area of research by using honeycomb structure and exploring the effect of heat transfer fluid (HTF) configuration and honeycomb cell angle on the thermal performance of the LHTES during melting and solidification processes. In this work, five cases were designed: case (a) was regarded as reference case; cases (b) and (c) were related to HTF configuration; cases (d) and (e) were used to study the effect of honeycomb cell angle. A numerical study was conducted using ANSYS FLUENT R19.3, followed by experimental validation. In this study, a good agreement is obtained from the validation process. Computational fluid dynamics (CFD) model results show symmetrical melting and solidification behavior when using a honeycomb structure. The results of the HTF configuration show a significant effect. For case (c) with a multiple water block, significant melting and solidification enhancements are obtained with 56% and 50%, respectively. Thus, the HTF configuration can improve the thermal performance of the storage. However, considering different honeycomb cell angles show an insignificant effect on the melting and solidification rates. [ABSTRACT FROM AUTHOR]

Adding metal fins to extend the heat transfer area is a viable and effective technology to improve the poor thermal conductivity of Phase-Change Material (PCM). The annular fin is the most common type due to the simple structure, but it weakens the natural convection. Under this condition, the spiral fin is proposed to overcome the poor natural convection. An experimental system was built with three vertical shell-tube latent heat storage units (LHSU), two of which employed annular and spiral fins with the same heat transfer area by taking one without fin as a reference. The melting and solidifying status, temperature distribution and comprehensive efficiency are used to evaluate thermal performance of three LHSUs. Experimental results show adding metal fins contributes to the heat transfer improvement, especially for spiral fins. Employing metal fins can weaken PCM natural convection, but annular fins have a lower weakening efficiency than spiral fins on PCM natural convection. Therefore, the spiral fins provide superior thermal performance with enhanced multi-circulation flows. Compared with annular fins, employing spiral fins can increase the average Nusselt number by 28.6%, the average heat transfer rate by 20.9%–58.2% in charging and discharging processes, and the average heat flux by 17.5%–53.8% in LHSUs. [ABSTRACT FROM AUTHOR]

Thermo-hydraulic behavior of a Phase Change Material (PCM) plays a crucial role in deciding the performance of Latent Heat Storage (LHS) devices. Discharge or Solidification is the prime portion that determines the performance of the LHS device. This work numerically models solidification in a vertical tube-in-tube LHS device. The phase change is accounted for using the fixed grid enthalpy porosity method. An independent numerical model built is validated with the experimental model. Dimensionless parameters, namely Rayleigh Number, Stefan number, Reynolds Number, and L/D ratio, vary in the range of 9.19x105 to 39.45x105, 0.2 to 0.5, 600 to 3000, and 1 to 15, respectively. Among all parameters, the Stefan Number has the greatest impact on the solid fraction and solidification time. For estimating the Solidification Time and Solid Fraction, correlations are proposed. [ABSTRACT FROM AUTHOR]

Phase-change materials (PCMs) attract much attention with regard to their capability of mitigating fossil fuel-based heating in in-building applications, due to the responsive accumulation and release of thermal energy as a latent heat of reversible phase transitions. Organic PCMs possess high latent heat storage capacity and thermal reliability. However, bare PCMs suffer from leakages in the liquid form. Here, we demonstrate a reliable approach to improve the shape stability of organic PCM n-octadecane by encapsulation via interfacial polymerization at an oil/water interface of Pickering emulsion. Cellulose nanocrystals are employed as emulsion stabilizers and branched oligo-polyol with high functionality to crosslink the polyurethane shell in reaction with polyisocyanate dissolved in the oil core. This gives rise to a rigid polyurethane structure with a high density of urethane groups. The formation of a polyurethane shell and successful encapsulation of n-octadecane is confirmed by FTIR spectroscopy, XRD analysis, and fluorescent confocal microscopy. Electron microscopy reveals the formation of non-aggregated capsules with an average size of 18.6 µm and a smooth uniform shell with the thickness of 450 nm. The capsules demonstrate a latent heat storage capacity of 79 J/g, while the encapsulation of n-octadecane greatly improves its shape and thermal stability compared with bulk paraffin. [ABSTRACT FROM AUTHOR]

Convection melting in metal foam under sinusoidal temperature boundary conditions is numerically studied in the present study. A multiple-relaxation-time lattice Boltzmann method, in conjunction with the enthalpy approach, is constructed to model the melting process without iteration steps. The effects of the porosity, phase deviation, and periodicity parameter on the heat-transfer characteristics are investigated. For the cases considered in this work, it is found that the effects of the phase deviation and periodicity parameter on the melting rate are weak, but the melting front can be significantly affected by the sinusoidal temperature boundary conditions. [ABSTRACT FROM AUTHOR]

Integrating a solar water heater (SWH) with a phase change material (PCM)-based latent heat storage is an attractive method for transferring load from peak to off-peak hours. This transferring load varies as the physical parameters of the PCM change. Thus, the aim of this study is to perform a parametric analysis of the SWH on the basis of the PCM's thermophysical properties. A mathematical model was established, and a computation code was developed to describe the physical phenomenon of heat storage/release in/from the SWH system. The thermal energy stored and the energy efficiency are used as key performance indicators of the new SWH–PCM system. The obtained numerical results demonstrate that the used key performance indicators were significantly impacted by the PCM thermo-physical properties (melting temperature, density, and latent heat). Using this model, various numerical simulations are performed, and the results indicate that, SWH with PCM, 20.2% of thermal energy on-peak periods load is shifted to the off-peak period. In addition, by increasing the PCM's density and enthalpy, higher load shifting is observed. In addition, the PCM, which has a lower melting point, can help the SWH retain water temperature for a longer period of time. There are optimal PCM thermo-physical properties that give the best specific energy recovery and thermal efficiency of the SWH–PCM system. For the proposed SWH–PCM system, the optimal PCM thermo-physical properties, i.e., the melting temperature is 313 K, the density is 3200 kg/m3, and the latent heat is 520 kg/kg. [ABSTRACT FROM AUTHOR]

Purpose: Fabrics with photothermal conversion functions were developed based on the introduction of shape stable composite phase change materials (CPCMs). Design/methodology/approach: Acidified single-walled carbon nanotubes (SWCNTs) were selected as support material to prepare CPCMs with n-octadecane to improve the thermal conductivity and shape stability. The CPCMs were finished onto the surface of cotton fabric through the coating and screen-printing method. The chemical properties of CPCMs were characterized by Fourier transform infrared spectrometer, XRD and differential scanning calorimetry (DSC). The shape stability and thermal conductivity were also evaluated. In addition, the photothermal conversion and temperature-regulating performance of the finished fabrics were analyzed. Findings: When the addition amount of acidified SWCNTs are 14% to the mass of n-octadecane, the best shape stability of CPCMs is obtained. DSC analysis shows that the latent heat energy storage of CPCMs is as high as 183.1 J/g. The thermal conductivity is increased by 84.4% compared with that of n-octadecane. The temperature-regulating fabrics coated with CPCMs have good photothermal conversion properties. Research limitations/implications: CPCMs with high latent heat properties are applied to the fabric surface through screen printing technology, which not only gives the fabric the photothermal conversion performance but also reflects the design of personalized patterns. Practical implications: CPCMs and polydimethylsiloxane (PDMS) are mixed to make printing paste and printed cotton fabric with temperature-regulating functional is developed. Originality/value: SWCNTs and n-octadecane are composited to prepare CPCMs with excellent thermal properties, which can be mixed with PDMS to make printing paste without adding other pastes. The fabric is screen-printed to obtain a personalized pattern and can be given a thermoregulatory function. [ABSTRACT FROM AUTHOR]

There is a great deal of research being done on the performance of solar collectors. Evacuated tube solar collectors are a mature technology that has proved reassuring performance for heat generation. However, low thermal efficiency remains their main challenge. Therefore, research to improve the efficiency of Evacuated Tube of Solar has continued to date based on some new approaches. The present study presented various designs of Evacuated Tube of Solar collector (ETSC) thermally enhanced by the addition of reflectors and thermal storage units with phase change materials and nanoparticles. The proposed models were assessed during different periods and different zones in Tunisia, especially in the Northern and Southern regions. This work established the energy balance of solar thermal systems determined by the input/output method. Assumptions and mathematical relations are presented for the proposed designs. Additionally, measured and regression useful energy as a function of the daily cumulative global solar energy of all ETSC-types was also evaluated. Research gaps in this field are identified and future research trends and directions are recommended. [ABSTRACT FROM AUTHOR]

• Nano Ti 2 O 3 was investigated as nano additives for the first time to synthesize composite PCM with paraffin wax. • The best mass fraction of nano Ti 2 O 3 (9 wt%) is given in this research. • The photothermal conversion rate is 76.96% for composite PCM. • The thermal conductivity of composite PCM has an enhancement of 37.8% compared to pure paraffin wax. • The latent heat shows a decrease of only 5.3% compared to pure paraffin wax. Organic phase change material (PCM) has gathered considerable interest in various fields, especially in solar photothermal conversion. Nanoparticles were often utilized to improve the photothermal and thermal performances of PCM. In this work, the nano-scaled particles are obtained by grinding coarse Ti 2 O 3 powder, then they have been successfully dispersed into paraffin wax with various mass fractions. The thermal and photothermal performances get an experimental evaluation. The results indicate that the latent heat is decreased with the mass fraction, while the photothermal conversion efficiency gets improvement with the mass fraction. The 9 % mass fraction gives the highest thermal conductivity with an improvement of 37.8 % and the photothermal conversion efficiency is about 80 %. Besides, these improvements are accompanied by a mere 5.3 % drop in latent heat, much lower than the mass fraction of nanoparticles. Nano Ti 2 O 3 is first reported as an ideal particle for photothermal conversion of PCM, and it is suggested that the mass fraction should be less than 30 %. [ABSTRACT FROM AUTHOR]

The current paper summarizes the development of nano‐enhanced phase change materials (NPCMs) using capric acid (CA) and manganese dioxide (α‐MnO2) nanoparticles. The nanoparticles were obtained by the green synthesis technique using the leaves of Ficus retusa plant. The obtained nanoparticles were used in 1%, 2%, and 3% weight fractions in the nano‐formulations. The field‐emission scanning electron microscopy (FESEM) was employed to confirm the morphological structure and energy‐dispersive X‐ray (EDX) spectroscopy was used for the elemental analysis of the synthesized nanoparticles. The crystallographic studies were done using X‐ray diffraction (XRD) spectroscopy. The Fourier‐transform infrared (FT‐IR) spectroscopy results showed that the insertion of nanoparticles did not disturb the chemical configuration of CA. The differential scanning calorimetry (DSC) analysis revealed that the developed nanocomposites had excellent thermal energy storage capability that lay within the range of 145–164 kJ/kg. Five hundred extended thermal cycles were carried out which showed that the developed PCM had excellent thermal reliability and can be useful for a year‐long application. The variations reported with 1% nano‐formulation was −1.43% to +0.53%, −0.03% to +1.52%, and −6.67% to 9.94% with respect to onset, peak melting temperature, and latent heat of fusion. The thermal gravimetric analysis (TGA) results showed that developed PCMs were stable within the working temperature range. The melting/solidification curve showed faster heat storage and release rates owing to the increased thermal conductivity. These developed PCMs are useful for photovoltaic/thermal and building applications. [ABSTRACT FROM AUTHOR]

As a new material, phase change energy storage materials have irreplaceable advantages and application value in building energy conservation and ecological sustainability. The commonly used solid and liquid phase change materials, due to the problem of easy leakage of solid and liquid phase change materials to a certain extent, restrict the development and application of phase change composites. Aiming at the low temperature solid liquid phase change material encapsulation technology, this paper introduces the low temperature phase change latent heat storage material and its phase transformation in packaging technology research status quo. The porous mineral adsorption phase change material, such as diatomite, expanded vermiculite and expanded perlite, and porous carbon based phase change composites based on expanded graphite were given priority to, as well as the preparation of aerogel phase change composite material technology. The load capacity, thermal performance and thermal conductivity of phase change composites are introduced. On this basis, the future research direction of solid and liquid phase variable composites is proposed, in order to provide some reference for the application and promotion of solid and liquid phase variable composites. [ABSTRACT FROM AUTHOR]

The melting process of phase change material (PCM) in horizontal latent heat thermal energy storage (LHTES) units with longitudinal and annular fins was experimentally studied under the same fin volume condition. The PCM melting time of the annular fin unit is reduced by 13.7% compared to that of the longitudinal fin unit. The annular fins are more responsive to the increase in heat transfer fluid (HTF) inlet temperature and the longitudinal fins are more responsive to the increase in HTF flow rate. After that, numerical studies were also performed for the two LHTES units to reveal in-depth the differences in heat storage processes. The results show that the longitudinal fins perform better in the early stage due to their larger contact area with the inner tube and a denser distribution near the inner tube. But it also limits the natural convection in the latter stage. The annular fins have better natural convection performance in the latter stage and therefore have better heat storage performance. Based on the analysis, a composite fin was designed to combine the advantages of longitudinal and annular fins. Numerical results show that the newly designed fin results in a 21.6% melting time reduction compared to the longitudinal fin model and a 9.5% melting time reduction compared to the annular fin model. Finally, two principles to guide the fin design in horizontal shell-and-tube LHTES units were summarized. [ABSTRACT FROM AUTHOR]

Latent heat storage technology is widely used in solar power generation. Aiming to enhance the energy utilization rate to a greater extent, an innovative fan-shaped structure has been proposed to construct the metal fins of the shell-and-tube thermal storage device. The enthalpy method is used to simulate the heat storage process and focuses on the influence of inlet conditions on heat transfer. The influence of the fin structure on the melting properties of phase change material has been studied. The results show that increasing inlet temperature and inlet flow rate is a convenient and effective way to improve energy efficiency. As the inlet temperature is increased from 343 K to 358 K, the total heat storage and energy efficiency are improved by 13.4% and 10.2%, respectively, and the melting time is reduced by 36.2%. As the flow rate is increased from 3 L/min to 9 L/min, the complete melting time is reduced by 33.4%. Energy efficiency peaks at a flow rate of 5 L/min. Reasonable optimization of the fin structure can enhance the natural convection circulation during the melting process and further improve the energy efficiency. The research results can guide the design and structural optimization of the finned tube heat storage device. [ABSTRACT FROM AUTHOR]

• Study heat recovery from double elliptical latent heat storage system. • Study on different alignments of both inner and outer ellipse pipes. • Increase the rate of heat recovery using nano-enhanced phase change material by 4.8. • Increase the rate of heat recovery using double wavy inner tubes by 1.26. This work investigates an optimal model of the heat recovery from a double elliptical latent heat storage system using wavy inner tubes and nano-enhanced phase change material (PCM). A discharging rate and time, as well as the PCM thermal distribution in a three-dimensional simulation, are evaluated considering various alignments for both inner and outer ellipse pipes. The use of two inner tubes in two different cases considering straight and wavy tubes is also examined, followed by influences of various concentrations and types of nanoparticles. The inlet temperature and Reynolds number of heat transfer fluid (HTF) are also examined. ANSYS-FLUENT software is used to perform the numerical simulation. RT 35 and Silicon Carbide (SiC) are employed as the PCM and nanomaterials, respectively. Water is also considered as the HTF with the Reynolds number of 900. Different values of 20 and 40 mm are proposed for the horizontal and vertical radii of the outer tube to examine the different orientations of the elliptical tube considering the inner radius ranged from 4.95 to 14 mm. The findings show that the vertical alignment of the inner tube compound in the centre of the horizontal position of the outer tube presents higher efficiency during the solidification process. Using double pipes in both straight and wavy configurations increases the surface area, which enhances the heat transfer rate, accelerating the solidification rate by 1.26 and 1.1, respectively. The PCM compound with SiC nanoparticles with 2% and 4% concentrations accelerates the discharging rate by 2.8 and 4.8 times, respectively, compared with the single straight inner pipe case. Furthermore, it is found that by decreasing the temperature of the heat transfer fluid from 285 K to 280 K, the total solidification time reduces from 48 to 39 min. [ABSTRACT FROM AUTHOR]

The aim of this report is to build a portable solar thermal bank based on a Scheffler reflector that is capable of boiling‐type cooking using HITEC as a thermal storage material. This report reviews the problems related to solar cooking and evaluates the novel layout of a portable solar thermal bank which includes a daily thermal storage vessel. This stove is in the shape of a cylindrical container filled with phase‐changing latent heat storage material. Inside the container, we provide a small gap taking into account the volumetric expansion of the phase change material (PCM) during the melting process. The solar thermal bank is charged in the sun. It is placed directly for a few hours under the focus of a Scheffler reflector, which charges the solar thermal bank with enough thermal energy stored. After a while, the cooking process can be completed by users using that stored heat. The top cavity is used as a cooking pot in a solar thermal bank. Cooking meals do not require direct sunlight, which is typical for most solar cookers. The portable solar thermal bank is an alternative for low‐income households and adapts to local traditions of indoor cooking. It is portable and can be used safely to cook indoors or outdoors. In this study, a solar cooker with a thermal storage device was developed using a PCM. The size of the stove has been calculated by calculating the energy consumption for two to three people. HITEC salt has been chosen as a phase change material for thermal storage, which will be used for cooking when there is no sunlight. It enhances the applicability of solar cooking and preserves cooking possibilities using energy stored throughout the day at low production costs. [ABSTRACT FROM AUTHOR]

In this study, beeswax is studied as a phase change material (PCM) to store heat due to its high latent heat. The disadvantages of using beeswax were its low thermal conductivity and high melting point. To enhance the thermal conductivity of beeswax, nanoparticles (of Al2O3, ZnO, and FeO) and other phase change materials are used to decrease its melting point. In the present investigation, the melting point of beeswax was lowered by the addition of other organic PCMs like lauric acid, capric acid, and coconut oil. FeO nanoparticles (3 wt%) were found to give the best result for thermal conductivity enhancement of 112% compared to Al2O3 and ZnO with enhancements of 18.78% and 15.56%, respectively, at 5 mass%. Coconut oil was used to decrease the melting of the beeswax as it was the most stable and easily available one resulting in a melting point of 52 °C. An investigation was performed to study the effect of hot fluid flow rates (1 LPM and 2 LPM) and inlet temperatures (60 °C, 70 °C, and 80 °C) on the charging time of beeswax composite. The study showed that 50:50 mass% of beeswax and coconut oil and its composite with 1 mass% of FeO nanoparticle give us the best result out of all the other composites. The charging time of the material was found to be 15 min less than the composite without nanoparticles. [ABSTRACT FROM AUTHOR]

• Pumped two-phase loop (PTL) integrated with thermal storage (LHS) is proposed. • Thermal response behaviors of PTL-LHS under step heat load are investigated. • Fast tracking and delay response is sequentially observed as heat load increases. • Thermal response behavior regime diagram is quantitatively recognized. • Variable flow rate optimization strategy is validated by comparative experiments. Pumped two-phase loop integrated with thermal storage is an emerging solution for the short-term high-heat-flux cooling. The transient microchannel boiling heat transfer of pumped two-phase loop (PTL) integrated with latent heat storage (LHS) under step heat load are experimentally investigated, with special focuses on dynamic thermal response of two-phase loop and latent heat storage unit. The transient thermal behaviors of PTL-LHS are determined based on the wide variations of heat load and flow rate. A thermal behavior regime diagram is proposed to quantitatively recognize the transient thermal response of PTL-LHS, depending on the heat load and flow rate. The results indicate that the fast tracking mode and the delay response mode are observed and sequentially experienced for PTL-LHS as the step heat load increases. With respect to delay response mode, thermal storage efficiency is high with short thermal storage duration but cooling performance is insufficient, while the transient thermal performances are contrary under the fast tracking mode. The increase of heat load accelerates the transformation of the heat transfer mechanism in LHS from sensitive-heat-dominated to latent-heat-dominated, while increasing flow rate is conducive for the enhancements of thermal capacity and thermal stability of PTL-LHS. Increasing heat load brings about a larger critical flow rate of the transient thermal behavior regime transition, and hence the range of flow rate tends to be larger for the delay response mode. Particularly, the proposed variable flow rate optimization strategy is validated by comparative experiments, showing better cooling performance (the average evaporator wall temperature decreases by 10 °C) and more remaining load of phase change material. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, the thermal performance of triplex-tube heat storage system consisting of RT55 phase change material and Cu metal foam composite was investigated to find out the most efficient configuration among 17 distinct models (M1-M17) categorized into 4 distinct classes. Under simultaneous charging and discharging conditions, the melt fraction and latent heat storage capacity were calculated and finally an enhancement parameter was formulated. Additionally, the multi-criteria decision-making methods such as Analytical Hierarchy Process (AHP) and Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) were employed to obtain preference-based optimized designs. The findings revealed that model M7 has the highest steady melt fraction of λ ss = 0.81 with 107% enhancement among the models having equal volumes of PCM and composite PCM, i.e., M3-M8. The fin-type model M13 and rhombus-type model M14 provide the larger space for enhanced convection that leads to a high steady-state melt fraction values of λ ss = 0.71 and 0.75, respectively. In addition, both AHP and TOPSIS techniques predict model M13 as the optimized choice among all models upon considering the equal weightage criteria for the steady-state melt fraction (λ ss), steady-state time (t ss), and rate of steady latent heat stored per unit cost (L ⁎ ). • Simultaneous charging/discharging of CPCM inside triplex-tube is studied. • Circular, segmented, fin-type, and rhombus-type filling of CPCM are compared. • Melt fraction, melting time, and latent heat storage at thermal equilibrium are presented. • System is optimized by multi-criteria decision making techniques (AHP and TOPSIS). [ABSTRACT FROM AUTHOR]

To enhance the convective heat transfer and overall thermal performance of horizontal latent heat storage (LHS) units, an innovative tree-shaped fin structure with perforations was introduced. A numerical simulation study examined the impact of perforation layers on the unit's overall performance. For a comprehensive analysis of the perforations' cumulative effect on the LHS unit, the Response Surface Methodology (RSM) was utilized to assess the influence of variations in perforation diameter and number on material consumption and heat exchange targets, deriving predictive correlations. The results indicated that compared to a non-perforated structure, the maximum improvement was observed with three layers of perforations, reducing material usage by 0.93%, while increasing the Nusselt number (Nu) and heat exchange by 10.19% and 36.51%, respectively. Moreover, the average temperature of the phase change material (PCM) in one and three perforated layers was higher than in the non-perforated tree-shaped fins, with complete melting times reduced by 5.37% and 2.51%, respectively. RSM results showed a negative linear correlation between increased perforation diameter and number with reduced material consumption, with the number of perforations having a more significant impact on heat exchange than their diameter. The Pareto optimal points obtained using the Non-dominated Sorting Genetic Algorithm II (NSGA-II) demonstrated lower material usage and higher heat exchange. Compared to the non-perforated tree-shaped fins, the Pareto-optimized solutions reduced material consumption by 2%–2.68% and increased heat exchange by 79.42%–94.45%. Analysis of the flow field, temperature field, and phase change process revealed that perforations significantly enhanced the mixing of PCM in different areas of the tree-like fins and secondary flow, with temperatures near the perforations increasing by 5–7K and flow velocity by 3–4 times, significantly promoting convective heat transfer. • Bionic fins were utilized to enhance synergy of convection – heat conduction. • The effects of fin arrangement on performance of heat transfer were studied. • The mechanism of convection affecting phase-change heat transfer was analyzed. • The optimal solution group was obtained by NSGA-II. [ABSTRACT FROM AUTHOR]

Renewable energy sources are more acceptable and reliable by using efficient and well-design thermal storage. Therefore, enhancing the thermal performance of thermal storage is extensively studied. In the current work, the latent heat storage is a shell and a finned tube heat exchanger, the end of the fins being connected by a coiled spiral. Numerical investigation of the latent heat storage was performed by a three-dimensional model, with experimental validation. The heat transfer in the latent heat storage is improved by dispersing aluminum oxide nanoparticles with concentrations of 1%, 4%, 7%, and 10%. The outcomes confirmed that the distinguishing design of spiral enhances the heat transfer by convection, consequently rising the temperature of paraffin and accelerating the melting process. Nanoparticles increase the paraffin's low thermal conductivity, thus reducing the time required for completing the melting process. The higher the nanoparticles concentration, the greater the reduction in melting time and the improvement in thermal conductivity, whereas the highest concentration of nanoparticles gave 19.5% and 33% reducing in melting time and improvement in thermal conductivity, respectively. [ABSTRACT FROM AUTHOR]

To improve the charging performance of the latent heat storage units, this paper performs a numerical simulation study of the melting of phase change material under various gradient straight fins employing the enthalpy-porous medium model. Based on the evolution of phase interface and temperature distribution, along with the variation of liquid phase fraction and Nusselt number, we analyze the sole effects of gradient-length and gradient-angle on the melting of the phase change material. Further, we gain the optimized-gradient fins by cooperatively adjusting the geometrical parameters of both the gradient-length and gradient-angle using response surface methodology. The introduction of natural convection of the formed liquid divides the melting process into three stages. Optimizing the geometrical parameters of straight fins could facilitate the fast second stage containing natural convection, leaving no (or less) room for the slow third stage without natural convection. Compared with the uniform fin structure, gradient-length and gradient-angle could reduce the total melting time at most by 48.9% and 8%, respectively. The largest reduction (56.6%) exists in the optimized straight fin structure with the gradient-length of 5.56 mm and the gradient-angle of 5.36°, involving only the first two melting stages without the third stage. [ABSTRACT FROM AUTHOR]

Limonene-based polymers have a growing interest as being renewable source-derived materials. Here, highly cross-linked porous polymers were synthesized by free radical copolymerization of water-in-oil (w/o) high internal phase emulsions (HIPEs) of limonene and ethylene glycol dimethacrylate (EGDMA). The bio-derived monomer content in the total monomer composition was set to 50 vol%. To vary the openness and permeability of the resulting porous copolymers, synthesized poly(limonene- co -EGDMA) (PLE-x) copolymers were processed via two different approaches as extraction (E) and lyophilization (L). Ultimately, the ring-porous PLE-E or PLE-L copolymers with different degrees of permeability were used as supporting matrices for the development of form-stable palmitic acid@poly(limonene- co -EGDMA) (PA@PLE-E and PA@PLE-L) composite phase change materials (PCMs). The chemical structure, pore morphology, specific surface area, and thermal properties of the PLE based supports and PA@PLE-E / PA@PLE-L composite PCMs were explored. BET specific surface areas of the ring-porous PLE-E and PLE-L frameworks were measured to be 20.5 m2.g−1 and 4.8 m2.g−1. In addition to that, the latent heats of the resulting composite PCMs were found to be 77.4 J.g−1 and 64.1 J.g−1, while the peak melting temperatures were 63.4 °C and 60.7 °C, for PA@PLE-E and PA@PLE-L, respectively. The bio-derived matrices based thermally stable leak-proof PA@PLE-x composite PCMs with proper latent heat storage (LHS) characteristics are ideal candidates as energy materials for passive solar heating applications due to their favorable phase change temperatures. [Display omitted] • Limonene was used as bio-derived building block for copolymer synthesis. • Porous polymer supports was synthesized by free radical copolymerization of w/o type HIPE of limonene and EGDMA. • Porous copolymers were used as supporting matrices to develop form-stable palmitic acid/poly(limonene- co -EGDMA) PCMs. • The resulting leak-proof composite PCMs were shown to be good candidates for solar energy based LHS applications. [ABSTRACT FROM AUTHOR]

An intermittent heat charging and discharging strategy is proposed for on-demand thermal utilization in a three-layer latent heat storage unit filled with nanoparticle-enhanced phase change materials. To optimize the utilization ratio of phase change materials, and the stored and released thermal exergy amounts, a multi-objective prediction and optimization methodology combining orthogonal experimental design, range and variance analyses, multi-nonlinear regression models, and non-dominated sorting genetic algorithm-II is introduced while considering the variables of nanoparticle concentration, heat transfer fluid velocity, and intermittent time interval. Results show that the time interval presents the most significant influence. Multi-nonlinear regression models for the above three variables are established with determination factors of 0.9871, 0.9625, and 0.9253, respectively. The ultimate optimal results are 0.8, 57094.03 J, and 43066.73 J, achieved at the three variables of 44.37 min, 0.38 m s−1 and 8.99%, respectively. The maximum verification error of 5.11% indicates the reliability of this methodology. The methodology aims to enhance the overall performance of the three-layer latent heat storage system by mitigating the constraints associated with single-performance optimization. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are promising options of thermal energy storage mediums. However, their low thermal conductivity and leakage issues remain the setback and limits the practical applications. In this work, Palmitic acid (PA)/copper foam (CF) composite PCMs have been prepared using the melting-vacuum impregnation method, with PA serving as the phase change material (PCM) and CF as the supporting material. The surface of CF with pore sizes of 15, 20, 25, 30 and 35 PPI (pores per inch) has been chemically modified with hydrochloric acid to increase the surface roughness of CF, strengthening the adsorption capacity of CF skeleton structure for PCM. The melting temperature and the latent heat of PA/CF composite PCMs were measured by differential scanning calorimeter (DSC) to evaluate the heat storage performance. The charging/discharging properties of the PA/CF composite PCMs have been experimentally investigated. At the same time, the solidification process of PA/CF composite PCMs was tested and analysed using infrared imaging technology. The introduction of CF to form composite PCM not only improves greatly the thermal conductivity of PCM but also prevents the leakage. The thermal conductivities of PA/CF composites have obtained a significant enhancement. The composite PCM based on 15 PPI CF has the highest thermal conductivity of 5.112 W/(m∙K), which is more than 31 times higher than that of pure PA. The 15 PPI sample melts at 61.4 °C with a latent heat of 174.788 kJ/kg and possesses the fastest charging/discharging rate. Besides, the prepared samples behave uniform temperature distribution and perfect shape-stabilization when cooled. The prepared samples have the high thermal conductivity and fast thermal response rate, and could play a crucial role in the field of heat storage and thermal management of electronic devices. • The thermal conductivity of 15PPI PA/CF is 31 times that of pure PA. • The 15PPI PCM storage/heat release efficiency is extremely fast. • The three-dimensional CF skeleton is benefit to external heat dissipation. • The 35PPI impregnation rate is 76.685% and the highest enthalpy is 204.376 kJ/kg. [ABSTRACT FROM AUTHOR]

High-efficient latent heat storage technology plays a crucial role in solar energy utilization. In this study, a shell-and-tube heat storage tank employing a novel fin structure has been proposed. A three-dimensional unsteady heat transfer model of the tank has been established. The effects of fin height, fin angle and fin number on liquid fraction, average temperature and heat storage rate have been investigated. The results show that the complete melting time of the phase change material in the novel finned tube is shortened by 66.4% compared with the finless structure. The melting time of the fins with heights of 34.20 mm, 42.75 mm, and 51.30 mm are shortened by 56.9%, 60.1% and 66.4%, respectively. When the fin height exceeds 51.30 mm, the melting rate remains almost unchanged. The fin angle is not the larger the better. Compared with the bending angles of 10°, 20° and 40°, the complete melting time of 30° is reduced by 14.0%, 11.6% and 6.4%, respectively. As the number of fins increases, the total heat storage time is shorter, but the total heat storage has also been reduced. The results can provide a good reference for design, operating, and energy-saving of latent heat storage systems. [ABSTRACT FROM AUTHOR]

For the numerical simulation of a heat storage based on phase change materials (PCMs) an enhanced model is presented, considering the physical effects of convection flow in the liquid phase as well as the volume change during phase change. A modified heat capacity is used to realize the phase change. The phase change material is initially defined as a liquid with temperature-dependent material properties. A volume force is added to the Navier-Stokes equations to allow a circulating flow field in the liquid phase and prevent flow motion in the solid phase. The volume change is implemented with the Arbitrary Lagrangian-Eulerian method. A laboratory phase change experiment was performed using the PCM RT42 with a melting temperature of 42 °C. The laboratory experiment was calculated numerically using the enhanced model to evaluate the numerical model and to investigate the influence of the simulation parameters on the thermal behavior of the PCM. The thermal conductivity is determined as the main influencing parameter. A good agreement of the simulated melting front throughout a major part of the laboratory experiment has been shown. COMSOL Multiphysics provides a default model for phase change, which neglects convection flow and volume change. Compared to the default model, the enhanced model achieves more accurate results but requires more computational cost for complex latent heat storage systems. Using the default model without convection can be reasonable, considering that the heat storage design is either over-dimensioned or a suitable correction factor must be applied. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a numerical study of a new high‐temperature metal hydride bed configuration integrating a phase change material (PCM) and equipped with heat pipes. The first half of the heat pipe is incorporated into the metal hydride (MH) tank and the second into the PCM domain to enhance heat transfer between two domains. A parametric study of different thermophysical and geometrical parameters of both media (MH and PCM) was carried out. In the simulations, the thermal conductivities of the MH and the PCM, the convective heat transfer coefficient, the melting temperature, and the number of heat pipes were investigated to evaluate their effects on the kinetics of absorption and melting of the PCM. Numerical results showed that the reactor performance improved upon increasing the PCM thermal conductivity, the convective heat transfer coefficient and the number of heat pipes and also by considering an optimal melting temperature, which ensures good hydrogen storage capacity in a minimum loading time. [ABSTRACT FROM AUTHOR]

The real-time change of solar radiation intensity leads to the instability of the outlet temperature of the collector, which has an important influence on the thermal performance of the thermal energy storage system. Therefore, the dynamic thermal performance of a packed-bed latent heat storage system integrated with a solar parabolic trough collector is studied in this paper. Moreover, the effects of different mass flow rates on the total charging capacity, total exergy input, total exergy storage and exergy efficiency of the system are investigated. The result indicates that the steady-state and unstable-state inlet boundary conditions show significant differences in thermal performance. Under the unstable-state boundary conditions, when the mass flow rate increases from 0.1 to 0.2 kg/s and 0.1–0.4 kg/s, the maximum temperature difference between the PCM capsules and the air decreases to 24.11% and 47.39%, respectively. The larger the mass flow rates, the smaller the temperature difference, which is the opposite of the steady-state situation. Under steady-state inlet temperature conditions, the exergy efficiency gradually decreases with the increase of mass flow rate. Under unstable-state inlet temperature conditions, the mass flow rate has little effect on the exergy efficiency, and which is about 41.00%. • The packed-bed latent heat storage system integrated with the solar parabolic trough collector is modeled. • The thermal performance under the steady-state and unstable-state inlet boundary conditions is compared. • The instantaneous energy efficiency decreases as the mass flow rates increases. • The exergy efficiency is about 41.00% under unstable-state inlet temperature conditions. [ABSTRACT FROM AUTHOR]