Search

Electronic devices are commonly used for exploiting and extracting shale oil in deep downhole environments. However, high−temperature−and−pressure downhole environments jeopardize the safe operation of electronic components due to their severe thermal conditions. In the present study, an active thermal−insulation system is proposed, which consists of a spiral annular cooling plate (ACP), a thermal storage container with phase−change material (PCM) and an aerogel mat (AM). The effect of the ACP's structure, layout and working−medium flowrate on the heat−protection performance were experimentally measured; temperature−control capability and system−operating time were used as the criteria. The results show that the AM layer is necessary and that the inner−ACP case displays better thermal−protection performance. Next, a dimensionless temperature−control factor (TCF) was proposed to evaluate the trade−off between temperature control and the system's operating time. Note that the TCF of the spiral ACP can be improved by 1.62 times compared to the spiral−ACP case. Since the lower flowrate allows better TCF and longer operating times, intermittent control of the flowrate with a 1−minute startup and 2−minute stopping time at 200 mL/min can further extend the system's operating time to 5 h, and the TCF is 3.3 times higher than with a constant flowrate of vm = 200 mL/min. [ABSTRACT FROM AUTHOR]

Non-isothermal melting phenomenon widely exists in phase change process where mixtures are utilized as phase change materials. It is in the mushy zone that phase transition actually occurs during the melting process. Thus, an in-depth understanding of flow and heat transfer in the mushy zone can provide beneficial ways to improve melting technologies. This article focuses on the evolution of mushy zone for low-Prandtl material under Neumann boundary condition. A two-dimensional model composed of liquid zone, mushy zone, and solid zone is established based on the improved enthalpy-porosity method. The pressure and velocity are coupled with SIMPLER algorithm based on the finite volume method with a Fortran code. The results indicate that the temperature on the heating surface is uneven, which are different from the results under Dirac boundary condition. The existence of mushy zone can supply a buffer to the unsteady melting adjacent to the heating surface initially. And the mushy zone experiences expanding stage and shrinking stage. More time is needed for complete melting and the average temperature on the heating surface gets lower under greater melting temperature range. Increasing Ra can result in augmentation of heat transfer in liquid domain and more inclined interface, and the heat transfer is dominated by heat conduction when liquid phase fraction is less than 20%, and thereafter, it is dominated by natural convection. For the same material, increasing heat flux obviously shortens the total melting time. And the mushy zone is reduced for that greater temperature gradient is produced in the mushy area. [ABSTRACT FROM AUTHOR]

To curb the greenhouse gas (GHG) and carbon emission in line with the Paris climate agreement, the road transportation needs to be electrified. The predicted electrification of the road transport can substantially reduce the GHG emission. The fundamental component in electric vehicles (EVs) is the power battery, in which its performance is affected by temperature. To improve the cooling performance and enhance temperature uniformity in the battery stack, a battery thermal management system (BTMS) comprising heatsinks with fluid channels and multi-phase change materials (PCMs) was investigated in this paper. The module consists of eight prismatic cells with nine fluid passages and PCMs attached at each side of the cell. The heatsink containing PCMs is separated into three equal portions, each is filled with different PCMs. The cooling effectiveness and temperature uniformity of the BTMS were carefully explored based on compactness of the battery stack and cooling fluids. The results indicate that increasing the PCMs thickness supressed the temperature rise by more than 2.85 K and provide better temperature uniformity compared to increasing the fluid channel width for the same volume of heatsink to volume of the battery unit ratio. Liquid cooling is more effective than air cooling in mitigating temperature especially at high ambient temperature. Choosing an appropriate ratio of volume of cooling channel to battery unit is particularly essential and can minimize operation cost. [ABSTRACT FROM AUTHOR]

With the aim to investigate heat transfer characteristics of PCM on micro-textured hot surface, this study numerically investigates the heat transfer process of PCM at fractal Cantor structured surfaces using the total enthalpy-based lattice Boltzmann method, which is partly validated by experimental testing. The thermal slip length and liquid velocity distribution are assessed as evaluation criteria. Results show that Fractal Cantor structure can significantly stimulate localized thermal convection, thereby reducing the average thermal slip length from 0.3 mm to approximately 0.14 mm. When the Fourier number exceeds 0.1, both thermal conduction and convection should be considered within the melted layer. With the fractal level increasing, a more uniform melt-front evolution can be observed, consequently, minimizing the total melting time by 500 s with the fractal level of 3. Elevating Ste and gravity can significantly increase the flow rate of liquid PCM by augmenting superheat degree and buoyancy effect, thereby enhancing convective heat transfer strength and reducing thermal slip length. According to the orthogonal design, though the fractal level demonstrates minimal range values for both maximum velocity and Rayleigh number, it elevates the sensitivity to the variation of boundary conditions. Ste yields the most significant enhancement in heat transfer performance. • Dynamic melting of phase change material at fractal Cantor structure is studied. • The total enthalpy-based lattice Boltzmann method is validated by experiments. • An orthogonal design is conducted to distinguish the weights of contributors. • Fractal Cantor structure can reduce thermal slip length from 0.3 mm to 0.14 mm. • Raising Ste and gravity can both enhance the heat transfer within melted layer. [ABSTRACT FROM AUTHOR]

• PCM capsules are used for thermal insulation of deice in downhole. • Various stacking structures of PCM capsules are numerically studied. • Shock properties including wave, area, frequency are analyzed. • The staggered structure shows the best thermal shock shielding performance. Pulsed power sources (PPS) are commonly employed for the exploitation and extraction of shale oil in deep downhole environments. Nevertheless, the extreme conditions, such as high temperature and high pressure, pose significant challenges to the safe operation of PPS systems due to electronic failures. In this study, capsules filled with phase change material (PCM) under three layouts are proposed, aiming to provide thermal protection and shock shielding for PPS devices. Numerical methods are applied to PCM capsules, and the properties of PCM capsules are obtained through experimental measurements. Results show that the staggered stacking structure shows the best thermal protection performance, with a phase change duration 14.1 % longer than that of the double layer stacking structure. Additionally, considering the effect of the shock wave generated by the PPS, the shock properties of the ordered stacking thermal protection structure at different phase transition stages and different structures are discussed. The double layer stacking structure has a smaller shock area, and the extreme range of the peak shock wave is 34.89 kPa, which is only 0.5 times that of the single layer array, but its internal shock frequency is larger than the latter. As a result, the staggered stacking structure is recommended, considering both thermal protection and shock shielding features. [ABSTRACT FROM AUTHOR]

The current research examines how increasing the thickness of the phase change material (PCM) layer impacts the thermal and economic behavior of the hybrid sensible-latent heat storage reservoir utilized in solar power plants in order to prevent temperature fluctuations at the end of discharge cycles. On the basis of two-phase dispersion-concentric equations, a detailed transient numerical analysis is developed. The mathematical model equations are computed using the MATLAB program, and the present numerical findings are validated. Numerical investigations are used to compare the proposed storage system to the sensible heat storage (SHS) system in the context of cost and efficiency. The impact of various performance evaluation indexes, including axial temperature allocation, thermocline layer degradation, charging time, discharging time, and overall efficiency, are investigated. The results showed that the (35% PCM-30% SHS-35% PCM) configuration possesses the most considerable thermocline thickness of 7.94 m at the charge period of 360 min, while the SHS case has 3.2 m thermocline thickness at the charge period of 420 min. Due to its optimized efficiency, reduced thermocline area, and comparatively low cost, the (15% PCM-70% SHS-15% PCM) configuration demonstrates a more viable choice among the considered cases. • The thermal performance of a hybrid sensible-latent heat storage tank is analyzed. • A numerical model is used for the thermo-economic evaluation. • Thermo-economic evaluation of increasing the thickness of the PCM layer. • The (15% PCM-70% SHS-15% PCM) configuration demonstrates a more viable choice. [ABSTRACT FROM AUTHOR]

The transition from gasoline automobiles to electric vehicles (EVs) is promoted as an alternative to reduce greenhouse gas (GHG) and pollutant emissions. The performance of EVs depends entirely on the performance of a power battery, especially the lithium-ion (Li-ion) battery, which is very sensitive to temperature. The temperature of Li-ion battery must be controlled and maintained within a desired range. This paper provides two aspects: (i) a review on research progress in battery thermal management (BTM) with emphasis on battery technology of commercial EVs and phase change material (PCM) based hybrid thermal management and (ii) a developed passive thermal management for prismatic Li-ion battery module under abuse operation condition. The hybrid thermal management combining PCM based with air/liquid/heat pipes can provide superior thermal performance than any active or passive alone. Improving the existing battery thermal management system along with exploring novel techniques to regulate thermal impact and power consumption are required. For the developed battery module, thermal performance based on finite element method is analyzed in a situation where the PCM content surrounding the batteries is reduced due to leakage or toppled over of PCM during melting process. Two different configurations are considered. The open medium configuration exhibited better performance in decreasing the maximum temperature by 1.172 °C, 1.396 °C, 1.628 °C, and 1.860 °C in the module at various PCM shrink levels of 2, 4, 6, and 8 mm, respectively. • An insight into commercial EVs battery technology and a comprehensive analysis of PCM-based hybrid BTMS are presented. • The advantages of hybrid BTMS over single passive or active BTMS are summarized. • A battery module operating under abuse conditions due to PCM leakage or toppled over of PCM during melting process is proposed. • The opened air medium configuration outperformed the closed air medium one in terms of temperature control in the proposed module. • The effect of various evaluation parameters such as cells spacing, shrink level of PCM, aluminum and contact resistance on thermal behavior are presented. [ABSTRACT FROM AUTHOR]

Perovskite Solar Cell (PSC) have recently emerged as exciting new candidates of Photovatics (PVs) for solar-to-electrical energy conversion. Nevertheless, one huge obstacle to its commercialization is how to improve its tolerance to operation at elevated temperatures. To address this issue, Composite Phase Change Material (CPCM) incorporated with a porous skeleton structure is proposed to integrate with PVs. In this structure, an important theoretical problem is that the temperature dependence of PV and the temperature control behavior of CPCMs interact with each other (bidirectional relationship). In this work, a pore-scale lattice Boltzmann phase change model is established to describe the dynamic thermal behavior of CPCMs and explore the roles of the bidirectional relationship between PVs and CPCMs, the change of power conversion efficiency influenced by temperature variation and glass transmissivity is discussed by comparing the overall liquid fraction of CPCMs, and the average temperature and power conversion efficiency of PVs. Furthermore, the situation of time-varying solar irradiation is discussed to mimic real application conditions. Results indicate that the neglecting temperature dependency of PVs leads to underestimation of PV surface temperatures and overestimation of power conversion efficiencies, while glass transmissivity provides reverse effects. These phenomena not only happen in constant solar irradiation but also in varying solar irradiation, calling for increasing attention to designing PV/CPCMs for varying heat flux conditions. The findings of this work establish a comprehensive manner toward integrated design of CPCMs for PV thermal control. • The roles of the bidirectional relationship between PVs and CPCMs are discussed. • Neglecting temperature dependency endows an overestimation of PV efficiency. • The highest temperature is underestimated if simplifying the variable heat flux to constant heat flux. • The temperature dependency of a PV has a slight influence on phase change. [ABSTRACT FROM AUTHOR]

The optimal performance of a Li-ion battery is directly impacted by temperature. In order to control the temperature rise and provide even temperature distributions in the battery pack, a thermal management scheme comprises thin heat sinks with multiple phase change materials (PCMs) and air channels is investigated in this paper. The cooling performance and temperature homogenization of the battery thermal management (BTM) system are carefully studied under various configurations of PCMs. The results show that increasing the air inlet velocity has less effect in suppressing the temperature rise at early discharge stage, but ameliorates as the discharge prolonged to 3600 s. The standard deviation of the temperature (STDV) and maximum temperature of the batteries can be decreased by arranging PCMs with a lower melting temperature at the midsection and a higher melting temperature at the air outlet region of the heat sinks. In addition, for volume fraction of PCMs, Case IV, having a PCM with a higher melting point adjacent to the air outlet region and occupying one-half the height of the heat sink, illustrates a lower temperature rise and decreases the maximum temperature in the battery module by 1.024 K, 2.186 K, and 2.553 K, compared to Case I, II, and III, respectively. • Multiple PCMs incorporated thin heat sinks for battery thermal management is proposed. • The thermal performance of the battery based on maximum temperature upsurge is investigated. • The distributions of PCMs based on melting point and latent heat were carefully explored. • The optimal design for the distribution of PCMs is obtained for the proposed battery. [ABSTRACT FROM AUTHOR]

Due to the characteristics of high energy storage efficiency, large energy storage capacity and constant phase change temperature, organic phase change materials have been widely used in the field of thermal energy storage. However, organic phase change materials present a lower thermal conductivity which emerges as a critical limitation to the energy storage efficiency of latent heat thermal energy storage systems. To improve the thermal properties, the superior composite phase change materials of graphene aerogel impregnated paraffin wax were prepared in present study. Hydrothermal reaction method was used to prepare aerogel. Optimal conditions for aerogel preparation were identified as 140 °C/2.5 h/90%/(1:100) (140 °C is the hydrothermal working temperature of the reactor, 2.5 h indicates a treatment time, 90% is the solution occupying the reactor volume and 1:100 is the graphene oxide (GO)/water ratio in the solution). Furthermore, the addition of ethylenediamine and graphene nanoplatelets accelerated the reaction process, which required a hydrothermal treatment time by 50%. For the composite phase change material PW-GO/GNP-3 with a GO/GNP mass fraction of 4.4%, the thermal conductivity was 209.7% of that for the pure PW and the energy storage efficiency was still maintained at 91.60%. Meanwhile, the composite phase change material exhibits a leakage ratio of lower than 3.8%. In addition, based on the prepared composite phase change material samples, the phase change characteristics of phase change material in single cavity and three-cavities have also been examined. The synchronous phase change in three-cavities has been obtained by arranging the phase change material with low melting temperature in the cavity with low temperature, which requires the shortest melting time. [ABSTRACT FROM AUTHOR]

Abstract Phase change materials used in thermal energy storage systems are critical for energy utilization. Organic phase change materials have received considerable attention both for applications and research due to their favorable properties, such as large latent heat, low cost, stability, nontoxicity, and corrosion resistance. Because of the inherently low thermal conductivity, there has been a lot of research on various combinations of organic phase change materials with high conductivity materials. Carbon nanotubes, graphene and porous carbon have excellent properties, such as ultrahigh surface area and high thermal conductivity, which have become the preferred materials for thermal properties enhancement. Benefit from the varied dimensional spaces for retaining materials, these carbon-based materials can act as excellent confinement for phase change materials to form shape stabilized, phase change tunable, and thermally enhanced phase change composites. In this paper, a review about recent advancement and challenges for organic phase change materials confined in different types of carbon-based materials is presented, associated with some relevant theories trying to understand the mechanism of heat transfer and phase change in micro/nano confinement. Some promising applications in thermal management and energy conversion that have great potential for more explorations are also introduced. Highlights • Carbon-based materials are suitable for infiltrating organic phase change materials. • The thermal properties of organic phase change materials can be improved effectively. • The challenges and perspectives of organic phase change materials are proposed. [ABSTRACT FROM AUTHOR]

• Thermal performance of multilayered PCM(s) thermocline TES tank is analyzed. • A numerical model is used for the thermal evaluation of thermocline configurations. • A parametric study of PCM melting temperature and heat of fusion is performed. • Results indicated the optimal values of melting temperature and latent heat for MLSPCM(s). The current paper presents two parametric studies (inverse Stefan number and dimensionless temperature difference) to optimize the values of latent heat and melting temperature of multilayered phase change materials (MLPCM(s)) in thermocline tank for concentrating solar power (CSP) plants. Spherical capsules filled with PCM(s) of different thermo-physical properties are used to fill the bed region, and the molten salt is used as heat transfer fluid (HTF). The numerical model that has been developed uses the Dispersion-Concentric (D-C) equations. By using MATLAB, the governing equations are solved and validated against the experimental results. The results show that in the optimal configuration of the case (B), the values of InvSte number and dimensionless temperature (θ m) are equal to 1.2 and 0.8 for the top PCM layer, respectively; 0.75 and 0.55 for the middle PCM layer, respectively; and 0.65 and 0.3 for the bottom PCM layer, respectively. Moreover, it is also found that to obtain the best design and distribution of temperature for a thermocline tank consisting of three layers of PCM, the top PCM layer should melts by Δ T = 55.4 °C below the HTF charging inlet temperature, the PCM layer at the bottom should solidifies by Δ T = 83.1 °C above HTF discharging inlet temperature. [ABSTRACT FROM AUTHOR]

With electronic device miniaturization and integration, its thermal management is encountering challenges of high heat flux and eliminating thermal stress. Phase change thermal control is paid more attention to due to its high energy density and temperature uniformity. Therefore, a visual experimental platform was established to investigate the heat transfer and phase change characteristics of graphene aerogel composite phase change materials in this study. The results indicate that the heat dissipation enhancement of those composite materials can reach 220.8%, while graphene aerogel has the opposite effects of heat conduction enhancement and convection suppression. Furthermore, two new cascade arrangements are proposed and the effects of cascade arrangements on heat transfer performance are discussed. The improvement effect is best when the thermal conductivity increases longitude from top to bottom, whose heat dissipation efficiency is 207.5%, which is 11% higher than that of the group without cascade configurations. The horizontal cascade arrangement proposed in this study achieves an effective combination of heat conduction enhancement and convection heat transfer. Its heat dissipation is 12% more effective than the cavity filled with pure CPMCs using the same amount of porous materials, and the phase change speed is increased by 149 s. • Heat dissipation enhancement of composite phase change materials prepared reached 220.8%. • Graphene aerogel has conduction enhancement and convection suppression effects. • Increasing the thermal conductivity from top to bottom enhanced heat dissipation by 11%. • Horizontal cascade arrangement improved convection and enhanced heat dissipation by 12%. [ABSTRACT FROM AUTHOR]

CO 2 hydrate is a potential cold thermal energy storage material with latent heat of 500 kJ/kg, however, the dissociation principle of CO 2 hydrate is different from that of solid-liquid phase change materials and therefore, exploring the dissociation mechanism of CO 2 hydrate is of great significance for efficient cold storage. In this paper, a new lattice Boltzmann model is proposed, considering dissociation kinetics, two phase flow, heat transfer, latent heat, surface reaction, thermal buoyancy and variable parameter depended with temperature. The necessity of the temperature consideration related with latent heat and buoyancy is clarified. For the combined effect of depressurization decomposition and thermal decomposition of CO 2 hydrate dissociation, depressurization decomposition diminishes as time increases and initial pressure increases and thermal decomposition enhances as hot wall temperature increases. The fully dissociated Fo is 0.544, 0.514, 0.604, 0.628, showing a first decreasing and then increasing trend while initial pressure increases from 0 to 0.002, 0.004, 0.006 lu. As hot wall temperature increases from 8, 10, 12–14 °C, the fully dissociated Fo is 0.566, 0.544, 0.473 and 0.419 respectively. This new lattice Boltzmann model is of significance in providing guidance for the future cold thermal energy storage system application by using CO 2 hydrate. • A lattice Boltzmann model with thermal buoyancy consideration is developed for the dissociation process of CO 2 hydrate. • The dissociation tendency of CO 2 hydrate is revealed when coupling depressurization and thermal decomposition. • Increasing initial environmental pressure reduces the dissociation rate, but prolongs the fully dissociated time. • Increasing hot wall temperature apparently accelerates the heat transfer and dissociation performance. [ABSTRACT FROM AUTHOR]

Latent heat thermal energy storage (LTES) has been recommended to complicated aerospace systems due to the excellent ability of storing thermal energy in recent years. Metal foam, as an effective additive to enhance the effective thermal conductive coefficient of phase change materials, has been wildly used in the LTES system. In support of the future space exploration, solid–liquid phase change within metal foam under different gravitational accelerations and corresponding heat transfer characteristics are investigated in this work to enhance understanding of heat transfer capability in reduced gravity conditions. A pore-scale lattice Boltzmann method with the double distribution functions is developed to study the solid–liquid phase change problems with the natural convection heat transfer in metal foam. Here, microstructure of metal foam is experimentally obtained by the use of X-ray computed tomography. Two numerical validation cases are performed, one for fluid–solid conjugate heat transfer problem, and the other for melting process in a square cavity without the porous media. The presented lattice Boltzmann results are in good agreement with previous analytical and numerical results. Based on the analysis of temperature and velocity fields during melting within metal foam, it is found that the clockwise circulation, caused by the temperature gradient, leads to the inhomogeneous distribution of liquid–solid interface along vertical direction. What’s more, gravity effects on the temperature and velocity fields together with the average Nusselt number and liquid fraction coefficient are investigated. Results show that with the decrease of gravitational accelerations from 1 g to 0 g , the maximum vertical velocity reduces and the thickness of velocity boundary layer thickens accordingly, and results in the pronounced reduction of average Nusselt number and melting rate. The natural convection appears to be even more tenuous as gravitational acceleration decreases, leading to the dominant heat transfer mechanism transited from convection to conduction, and finally alleviating the phase change process. The liquid fraction under 0 g , 0.01 g and 0.1 g conditions are 54.6%, 58.9% and 67.9% respectively of that under 1 g conditions at Fo  = 0.06. In addition, porosity effects on phase change heat transfer characteristics are discussed by comparing the liquid fraction with porosity of 0.9, 0.94 and 1. It is found that metal foam with lower porosity shows higher effective thermal conductivity and outstanding heat transfer performance, while the restriction on natural convection should not be neglected, especially for melting region which is dominated by natural convection. [ABSTRACT FROM AUTHOR]

In applications of solar energy, thermal ratcheting is a crucial topic connected to the periodic performance of dual-phase thermocline storage tank. In order to investigate this phenomenon, a detailed simulation of a thermocline reservoir that includes both the hybrid tank wall and the varied filling zone is necessary. The thermo-mechanical characteristic of the cascaded layers storage tank for parabolic trough power plants is examined in the current work using one parametric study (dimensionless temperature difference) to determine the impact of changing the melting temperature of the phase change material (PCMs) layers. Experimental work from earlier studies is utilized to validate the numerical outcomes currently being presented. The results showed that structures-VIII and XIV have acceptable thermal performance, but ineffective mechanical performance since the normalized stress values were greater than one. The structure-XIII has the best overall efficiency of 79.58%, followed by structures-II, III, and XI, with performance levels of 70.82%, 67.83%, and 66.85%, respectively. The lowest overall efficiency attains by structure-XII, which equals 22.21%. The energy retrieved, overall efficiency, capacity ratio, and utilization ratio for the best scenario "structures- XIII ″ are 188.2 MWh, 79.58%, 44.34%, and 40.5%, respectively, based on the charging/discharging duration. • A numerical model of cascaded layers storage tank for PTP plants is addressed. • Thermo-mechanical analysis of varying the melting temperature of each PCM layer. • The normalized stress values for structures-VIII and XIV are greater than one. • Based on the charging/discharging period, structures-XIII is recommended due to its 188.2 MWh energy recovery. [ABSTRACT FROM AUTHOR]

• Cellular thermosyphon (CET) fin and cycloid thermosyphon (CYT) fin are tested. • CYT fin performs 10.1% improvement on average thermal resistance. • Reasonable computational model is developed based on VOF and Lee model. • CYT fin is optimized with four vapor zones, showing 8.7% higher liquid level. The aluminum fin integrated with thermosyphon loop is a good alternative for improving the thermal dissipation from the heat source, which has light-weight and high-efficiency features due to the charge of phase change working fluid. However, the criteria for flow channel arrangement and corresponding heat transfer mechanism in thermosyphon fins are still not clearly acknowledged. In present study, the cellular thermosyphon fin (CET fin) and the cycloid thermosyphon fin (CYT fin) are experimentally tested. Result shows that the CYT fin always illustrates much better temperature distribution and performs about 10.1% improvement on the average thermal resistance. Then, the pool boiling and condensation in CET and CYT fins are further explored via numerical investigation. It is found that the existence of vapor cavity in blind channels may enhance the condensation as well as promote the liquid level on the heat source side. Consequently, a total of four optimized configurations based on the tested CYT fin are proposed and numerically studied. Result shows that the optimum configuration with four vapor zones in one partition (4-in-1 case) possesses 8.7% higher liquid level compared with the original CYT fin. The increments on the evaporation rate and condensation rate can reach 12.7% and 10.7%, respectively, and lower fin root temperature is also achieved. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) have been considered suitable energy materials to address the mismatch between energy demand and supply to improve the utilization efficiency of the latent heat thermal energy storage (LHTES) system. However, the relatively low thermal conductivity of PCMs leads to an undesirable thermal response rate of the LHTES system. Among the common methods to improve the heat transfer performance of PCMs, the employment of metal foam (MF) has attracted growing attention as an effective strategy. Plenty of studies have investigated thoroughly the vital parameters of MF impacting the phase change process, while a corresponding discussion of the situations and limitations of the known technologies is still lacking. In this review, a total of 476 literature derived since 2000 are visualized based on scientometric analysis to exhibit the attractive spotlights and new trends. The impact factors on the heat transfer performance of PCMs embedded with MF (PCMs/MF) are presented in-depth. Besides, the developments of hybrid heat transfer enhancement techniques based on the MF are overviewed comprehensively. Combined with the thermal characteristics of typical applications, systematic information on PCMs/MF in these applications is summarized, and the suitability of these technologies is discussed. Finally, ongoing challenges of PCMs/MF are identified, and developmental tendencies and opportunities for further research work to address them are discussed. This review provides helpful information to facilitate the development of innovative and feasible PCMs/MF in the LHTES system and encourage and attract researchers and scholars to get some advancement in their future work. • Scientometric analysis is used to exhibit attractive spotlights and new trends. • Impact factors on heat transfer enhancement of PCMs/MF are presented. • Effects of hybrid enhancement techniques based on MF are overviewed. • Systematic information on PCMs/MF in typical applications is summarized. • Challenges and prospects of PCMs/MF are identified. [ABSTRACT FROM AUTHOR]

The development of phase change materials (PCMs) is hampered by issues like leakage, poor thermal conductivity, and poor light absorption. In this study, we innovatively combined modified melamine foam (MF) and graphene nanoparticle (GNP) to address these defects of PCMs in the solar-thermal energy system. The MF was modified to endow the solar-thermal energy conversion ability and superhydrophobic interface characteristics due to the polypyrrole (PPy) by the in-situ polymerization and the polymerized octadecylsiloxane (PODS) layer coating on the sponge skeleton. The composite PCMs consisting of the modified MF, paraffin wax (PW), and GNP were fabricated and exhibited good leakproof ability, high thermal conductivity, and excellent solar-thermal energy conversion capability. Results showed that due to the effects of the PPy and the PODS on the sponge skeleton structure, MF@PPy-PODS/PW composite PCMs showed a decrease in the mass loss ratio to less than 0.34% and an increase in the thermal conductivity of 0.33 W/m·K and the solar-thermal storage efficiency of 75.68%. Besides, adding GNP with higher concentrations impacted positively on the thermal conductivity and the solar-thermal energy conversion ability but negatively on the phase change enthalpies. MF@PPy-PODS/GNP3/PW composite PCMs increased the thermal conductivity to 0.59 W/m·K and the solar-thermal storage efficiency to 79.36% while decreasing the phase change enthalpy to 130.61 J/g. Furthermore, a thermoelectric conversion system driven by solar energy was developed to show the potential of composite PCMs for cleaner energy production. The open-circuit voltages of the MF@PPy-PODS/GNP3/PW composite PCMs achieved 0.78 and 0.91 V at 2 and 4 Sun, respectively. The open-circuit voltages remained for a period of time and slowly dropped without the simulated solar light irradiation. This study provided a potential strategy for the optimal performance of composite PCMs and their application in solar thermal systems. • PCMs composited with modified melamine foam and graphene nanoparticle were prepared. • Composite PCMs showed good leakproof ability and high thermal conductivity. • Solar-thermal storage efficiency of composite PCMs achieved 79.36%. • Open-circuit voltage in solar-driven thermoelectric conversion system was improved. [ABSTRACT FROM AUTHOR]

The heat exchanger is an essential component of the supercritical CO 2 Brayton cycle. To attenuate the temperature fluctuations in the cycle, this study proposes a new structure with phase change materials embedded in the printed circuit heat exchanger. This structure package can contain a variety of phase change materials in a stepwise arrangement and a composite phase change material with expanded graphene. The effects of different flow directions, the number of layers in the phase change material ladder, whether the phase change material is compounded with expanded graphene or not, and the thickness of the phase change material were numerically compared. The results show that the PCM layer with 0.45 mm thickness has a smaller amplitude of both temperature fluctuations and liquid fraction fluctuations than that of 0.25 mm. Relative to the case without PCM, the outlet of hot side' temperature fluctuation amplitude of PCM/EG-3 and PCM/EG-5 with 0.45 mm thickness decreased by 17.11% and 22.37%, and the outlet of cold side' temperature fluctuation amplitude decreased by 36.84% and 38.16%, while the heat exchange decreased by only 2.28% and 1.78%, respectively. • A new structure for PCM embedded in PCHE is designed. • The effects of flow direction on the performance of PCHE-PCM are compared. • The effects of a multi-layer PCM ladder arrangement on PCHE-PCM are investigated. • The composite structure of PCM/EG significantly reduces the heat loss of PCHE. • The effects of different PCM layer thickness on PCHE-PCM are investigated. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) devices play an increasingly important role in solving the energy crisis. However, the conversion efficiency of the PV panel is small. Cooling of PV panels using phase change devices is an effective way to improve the working performance of PV panels. A phase change device with a two-level arrangement of metal-organic phase change materials (PCMs) is proposed. The PCM is filled in a metal cavity made of aluminium plates. A numerical model of the melting process of the combined PCMs is established, and the flow and heat transfer characteristics of the melting process are analysed. The results show that the temperature variation curve of the metal cavity wall close to the PV panel can be divided into three main stages according to the temperature increasing rate, i.e., the first rapidly rising stage, the slowly rising stage and the second rapidly rising stage. The temperature distribution inside the metallic cavity is more uniform compared to the temperature distribution inside the organic material cavity, and the flow in the metallic cavity is weaker, and the temperature controlling time shows a unimodal variation with the increase of gallium filling proportion in the studied ranges, and the optimal filling proportion is 56.9%. [Display omitted] • Solve the dimensionless temperature and velocity governing equations simultaneously. • Ambient and melting temperature influences different stage of temperature rising. • The flow in the metallic cavity is weaker than that in the organic cavity. • The temperature controlling ability of 2-stage heat sink is better than 1-stage. [ABSTRACT FROM AUTHOR]

• A modified mixture theory for PCM and PCM/meta foam melting is presented. • A new constituential heat flux term and a new internal energy supply are proposed. • Thermal non-equilibrium effect and volume change from phase change are considered. • Three cases including Pure PCM, PCM/copper foam, PCM/nickel foam are studied. • Results by considering liquid flow show a good prediction to temperature field. Phase change materials (PCMs) have been attracting researchers' attention in the last few decades for their great potential in energy storage. Nevertheless, the precise modeling of phase change problem of PCMs and PCM composites remains a problem due to the extra complexity generated by interactions between several constituents. In our study, we propose a modified mixture theory framework for one-dimensional pure PCM and PCM/metal foam composite melting problems, which allows us to study the thermal interactions between each constituent. In this modified mixture theory model, the local thermal non-equilibrium effect is considered, and the velocity correlated to the density change during paraffin melting is introduced. A new constituential heat flux term is presented to explain the heat supply from different constituents, and a new interpretation for internal energy supply term is introduced. The governing equations are numerically solved by using finite difference method. Temperature field, mushy zone evolution, and velocity profile at the boundary are predicted. Experiments are conducted to validate the numerical analysis. By comparing the temperatures at 4 positions, it is shown that the numerical results obtained by the mixture theory model have a satisfying agreement with the real situation. [ABSTRACT FROM AUTHOR]

• Increasing nanoparticle concentration and ultrasonic power improves TES rate but decreases TES efficiency. • Enhancement mechanism of combined effects between nanoparticle and ultrasonic field is analyzed. • Initiating ultrasonic at latent process offers a higher TES efficiency. • Priority relationship between TES rate and TES efficiency needs to be considered. To further improve the performance of thermal energy storage (TES) system with phase change materials (PCMs), this paper proposed a novel method, i.e. combining the additions of TiO 2 nanoparticles, metal foam and the provision of ultrasonic field, investigated its synergetic effects in enhancing conduction and convection heat transfer. The thermal characteristics, including the TES time distributions and the energy consumption of the TES system, were discussed to evaluate the combined effects of TiO 2 nanoparticles and ultrasonic field on the TES rate and TES efficiency. The results showed that the latent TES time reduction index reached 46.50%, when the TiO 2 nanoparticles concentration was 5.0 wt% and the ultrasonic power was 100 W, while the TES efficiency dropped to 10.66%. Increasing TiO 2 nanoparticles concentration and ultrasonic power positively improved the TES rate due to conduction heat transfer enhanced by nanoparticles and convection heat transfer enhanced by the acoustic streaming effect and the cavitation effect of the ultrasonic field, but which negatively reduced the TES efficiency mainly due to the energy consumption of the ultrasonic field. Therefore, the effects of the ultrasonic field introduced at four action stages on the TES rate and TES efficiency were compared, and it confirmed that introducing ultrasonic field at the latent TES stage was better than that in the sensible TES stage. Additionally, the proposed novel combined method needed to consider the priority relationship between TES rate and TES efficiency for designing the TES system, favoring the potentials for further advances in TES applications. [ABSTRACT FROM AUTHOR]

• Dynamic melting is characterized by a pore-scale lattice Boltzmann model. • Selection of phase change material for photovoltaics thermal management is studied. • A low melting temperature offers a quick response but with a short duration. • A high latent heat offers high energy density while taking a long time to melt. Composite Phase Change Materials (CPCMs) using metal foam as core material are highly promising for thermal management of photovoltaics. Selecting a proper CPCM for a given application is challenging. To address this, we developed a pore-scale lattice Boltzmann model based on X-ray micro-Computed Tomography to describe the complicated microstructures of the metal foam and computed the dynamic temperature and flow fields in representative applications. Two important parameters for the design of PCMs, melting temperature and latent heat, are discussed in this work by comparing the melting fraction, energy density, and power density for different CPCMs. Further, we demonstrate a CPCM choice for thermal management of a tilted photovoltaic panel. By comparing the thermal behavior of four different paraffin based CPCMs having similar thermophysical properties but different melting temperatures and latent heats, the effects of melting temperature and latent heat are illustrated for a practical application. Compared with the highest latent heat (Stefan number Ste = 0.1), energy density is reduced by 31.8%, 52.0%, and 63.5% for the other three cases with Ste of 0.15, 0.22, and 0.3, respectively, while the melting time is extended, with the reverse order. Besides, a lower melting temperature leads to a quicker response at the early melting stage, while this quick response is short-lived. Thus, the choice of melting temperature should balance the benefits of excellent initial thermal control against the risks of loss of control later. The results of this work help establish an effective strategy toward material selection of CPCMs. [ABSTRACT FROM AUTHOR]

Photovoltaics, as a direct technology to convert sunlight into electricity, possess significant potential to deal with ever-increasing environmental problems and the desire to reduce the use of fossil fuels. Thermal stability of photovoltaics is of major concern when considering large-scale commercialization under conditions in which device degradation by high temperature operation is possible. Phase change materials (PCMs) are highly promising for thermal management of such devices due to their high latent heat and inherent heat transfer properties. However, a great challenge in applying PCMs to photovoltaics is in achieving high energy density while maintaining high power density, especially with different orientations of the photovoltaics. In this work, the dynamic heat transfer characteristics of a composite PCM with embedded metal foam are systematically studied by a pore-scale lattice Boltzmann model. It is found that the melting rate of composite PCMs dramatically decreases at late-stage melting, leaving a region of solid PCM ("dead zone") for a long time. To address this issue, we propose a special, nonuniform structure for the composite PCM that has a different porosity in the dead zone than elsewhere. The melting rate, energy density, and power density of the composite PCM can be significantly enhanced by tailoring the porosity of the composite metal foam. For instance, at a Fourier number of 0.30, the energy density of a case with a dead zone porosity of 0.80 is 6.8% higher than that with a dead zone porosity of 0.95. This work provides an effective strategy toward applying PCMs for thermal management of photovoltaics and paves a way toward optimizing energy storage capabilities of PCMs under various working conditions. [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide (SCO 2) Brayton cycle is widely known as highly potential bottoming cycle among energy conversion systems in the future due to its low requirement to heat source, high efficiency and small volume. Recently, SCO 2 Brayton cycle has been considered utilized in marine industry. In marine environment, unstable disturbance due to the oscillating condition driven by wind and waves makes an impact to on the dynamic performance of SCO 2 Brayton cycle. In this study, we proposed a novel type of compact heat exchanger coupled with phase change material (PCM) based on the concept of printed circuit heat exchanger (PCHE) as a transient controlling method in order to stabilize the dynamic performance of main compressor, re-compressor and turbine in the SCO 2 recompression Brayton cycle system. In this paper, dynamic modelling of the SCO 2 recompression Brayton cycle system with designed PCM based heat exchanger is developed and its dynamic performance is tested. The result of the transient simulation shows that with the effect of PCM based heat exchanger, the disturbing ranges of compression and expanding power of the main compressor, re-compressor and turbine decrease at most by 84%, 75%, and 95% respectively, and the disturbing range of efficiency is reduced by 94%. The PCM based heat exchangers are proved to have great effect on reducing disturbing amplitude of performance of turbo machineries and cycle parameters. • A novel type of PCM based heat exchanger which fits SCO 2 cycle is proposed. • The thermal design and dynamic numerical modeling of PCM-PCHE are developed. • Designed PCM-PCHEs highly reduce disturbing response range of working parameters. • PCM-PCHE in front of turbine impact most on cycle efficiency and output power. [ABSTRACT FROM AUTHOR]

• Melting of composite PCMs with void cavities is characterized by lattice Boltzmann model. • Void cavities can suppress thermal energy performance of composite PCMs. • Melting process is hindered with increasing volume fraction of void cavity. • Difference between near-wall and randomly distributed void cavities is identified. Composite Phase Change Materials (PCMs) incorporated with metal foams are promising candidates for thermal management for space exploration. However, void cavities are generated as a result of the volume change of PCM during the melting process, introducing a resistance to heat transfer due to the low thermal conductivity of the void. In this work, the effects of void cavity distribution on the conduction-dominated melting of composite PCMs under microgravity conditions are studied by a two-dimensional pore-scale lattice Boltzmann method, in which a microstructural description of the metal foam is experimentally characterized with the help of X-ray micro-Computed Tomography. Two typical distribution patterns of void cavities are analsed and computed performance is compared (1) a near-wall void cavity, and (2) randomly distributed void cavities. The evolutions of temperature distributions and melting interfaces are compared, and the average liquid fraction and energy stored per width are deduced to describe the energy storage performance. Moreover, the influence of the volume fraction of void cavities is investigated by comparing temperature distributions and energy storage performances of composite PCMs with four different volume fractions of void cavities (0%, 3.7%, 7.6%, 15.2%). After introducing void cavities, the energy stored per width is reduced by 5.7%, 12.3% and 20.2% for randomly distributed void cavities when volume fraction of void cavities is 3.7%, 7.6%, and 15.2%, respectively, and reduced by 42.2%, 64.1% and 79.7% for the near-wall void cavity, respectively. This work initiates the study of the effects of void cavity distribution on composite PCMs, which will stimulate work on structural optimization of thermal management systems. [ABSTRACT FROM AUTHOR]

Energy-harvesting devices, consisting of thermoelectric modules and phase change materials (PCMs), can extract energy from the ambient environment for the self-power supply of many small electronic devices such as wireless sensors. However, due to the distinct temperature ranges of various seasons in different places, these devices' power generation performance may be seriously impaired. In this paper, a new double-PCM-based thermoelectric energy-harvesting device based on temperature fluctuations in the ambient environment is proposed to improve device performance. A double-PCM-based device has been built and tested in an environment with a large temperature range (0–40°C) for three days. Experimental results show that the average output power of the double-PCM-based thermoelectric energy-harvesting device under matched load resistance outperforms that of the single-PCM device by 35.8%. A one-dimensional unsteady heat transfer model is established to describe the temperature variation of PCMs. The influence of phase change is considered through variations in PCMs' specific heat capacity. This work demonstrates that the proposed double-PCM-based thermoelectric energy-harvesting device performs better over a large temperature range and is more suitable for small electronic devices operating at different times and in different places. • A double-PCM-based thermoelectric energy-harvesting device is proposed. • A one-dimensional unsteady heat transfer model is established for PCMs. • Average power of double-PCM device is 1.48 mW with four peaks in one period. • Output power of double-PCM-based device outperforms that of single-PCM device by 35.8%. [ABSTRACT FROM AUTHOR]

• Heat transfer of gallium in three-dimensional spaces is examined by experiment. • A piece of solid gallium is deposited at the end of melting due to weaken convection heat transfer. • Overall and most of melting time of gallium heat sink are reduced by 55.5% and 56.0% respectively. Phase change thermal storage technology has received considerable attention in the thermal management of electronic devices. Unfortunately, the efficiency using paraffin is too low to meet the heat dissipation requirements of high power devices. In this work, gallium is selected as the phase change material, and the melting mechanism of gallium heat sink in spatial distributions is examined by experiment. Results show that the heat transfer efficiency of regions in the Y -cross section near the heating surface and in the X -cross section near the upper surface of the gallium heat sink are better than other regions. The average effective thermal conductivity of the gallium heat sink reaches 71.97 W/(m·K). The natural convection promotes the overall melting rate, but it results in the inefficient heat transfer in the middle melting stage and worse heat transfer in the later melting stage. Compared with the copper foam/paraffin composite heat sink in the same size, the overall and most of melting time of the gallium heat sink is reduced by 55.5% and 56.0%, respectively. At the same thermal storage capacity, the volume and weight of the gallium heat sink are reduced by 67% and 18%, respectively, compared with the copper foam/paraffin composite heat sink. [ABSTRACT FROM AUTHOR]

• The effect of PCM volume fraction for three-layers TES tank is investigated. • A numerical model is used to define the temperature distribution of molten salt. • The thermal/economic performance of the three-layers thermocline tank is evaluated. • The bottom PCM layer with a higher VF has the lowest capacity cost of $38/kWh. The current paper investigates the phase change material (PCM) volume fraction (VF) effect on the thermal and economic behavior of a three-layer thermocline thermal energy storage (TES) tank system which is used in concentrating solar power (CSP) plants. The one dimensional transient dispersion-concentric (D-C) scheme is applied to calculate the phase change inside each capsule. Using MATLAB software, the numerical model equations have been figured out, and the current numerical results have been verified. Four different scenarios have been created to investigate the effect of PCM-VF on the thermal behavior and economic feasibility of the TES tank. The results described that the overall efficiency and the cost of capacity for all cases in order from the case (1) to the case (4) are 80.77%, 64.32%, 73.43%, 85.58%, and $45.37/kWh, $60.49/kWh, $46.28kWh, $38.58/kWh, respectively. Furthermore, case (4) demonstrates the storage capacity of 149 kWh/m3, which is 7.21%, 19.42%, and 15.78% higher than case (1), (2), and (3), respectively. In the comparative study, the results showed that case (4), which has higher VF for the bottom PCM layer, indicates that it is the most viable option of all the studied cases due to its best performance and relatively low cost. [ABSTRACT FROM AUTHOR]

• A three-dimensional pore-scale lattice Boltzmann model is developed for charging. • Primary natural convection and secondary convection interplays during charging. • Increasing gravitational accelerations make the melting interfaces more inclined. • The distinction between two-dimensional and three-dimensional models is identified. Latent heat thermal energy storage with metal foams has been considered as a promising candidate for thermal management in aerospace systems. Thus, there is good cause to deeply explore the heat transfer mechanisms of phase change material (PCM) melting with metal foams. In order to get close to the real situation, a three-dimensional, pore-scale lattice Boltzmann model is explored based on a three-dimensional reconstructed porous structure morphology taken from experimentally observed in this paper, to characterize the distribution of flow and temperature fields during charging of porous PCM. The gravity effects on heat transfer performance are documented by comparison of charging at different accelerates. During the charging process, nonuniform temperature distributions and inclined melting interfaces are presented at the latter stages, caused by the interplay of primary natural convection in the melting direction and secondary convection in the transverse direction. More inclined melting interfaces are observed as gravitational acceleration increases, yielding faster PCM melting in the upper region while melting in the bottom region almost terminated. This implies that natural convection gradually dominates heat transfer and leads to the temperature nonuniformity. Similar shape characteristics of melting interface are observed in two-dimensional model, while there is an apparent difference of the melting fraction, showing it gradually growing from 4.1% to 8.6% with increasing gravitational acceleration. These results indicate that secondary convection effect neglected in the two-dimensional model, leading to a significant error in the prediction of heat transfer performance. [ABSTRACT FROM AUTHOR]