Liquid Phase Change Material Research Articles

Experimental study on pressure-enhanced close contact melting with PCMs for stable temperature control of high heat flux electronic devices

Phase change material (PCM) demonstrates great potential for the thermal management of electronic devices. However, stable temperature control is hardly achieved because of the moving melt front during the phase change process. This study presents the pressure-enhanced close contact melting method for PCM, from the application aspect via visualization study. The overheated liquid PCM can be rapidly removed from the heat source, thus achieving stable temperature control for electronic device when operating under high heat flux. The transient performances of paraffin and low melting point alloy are evaluated, respectively, under various heat loads and pressures. It is recognized from the visualization test that the conventional PCM-based and metal foam-enhanced heat sinks fail to achieve stable temperature control since the continuously elevated liquid thickness between melt front and heat source results in increasing thermal resistance. However, the pressure-enhanced close contact melting method might continuously squeeze melted liquid, thus promoting the contact of melt front with the heat source. The effects of applied pressures and heat loads on the transient thermal management performance over time are virtually investigated. As the result, the surface temperature of heat source can be stabilized around the melting point of PCM. When applying the pressure of 2250 Pa, the thermal resistance can be minimized to lower than 10−4 K·m2·W−1. It is also noted that the thermal management performance remains unchanged when the pressure exceeds 1250 Pa.

Halloysite-based aerogels for efficient encapsulation of phase change materials with excellent solar energy storage and retrieval performance

Developing low-cost composite phase change materials with good shape stability, excellent mechanical strength, high thermal conductivity, large encapsulation ratio, strong light absorption and eminent solar-to-thermal conversion capacity is of great challenge to solve the scaling-up related issues of organic solid–liquid phase change materials during the utilization of solar energy. In this work, halloysite/poly(vinyl alcohol) and halloysite/poly(vinyl alcohol)/reduced graphene oxide aerogels with rich three-dimensional honeycomb structure were prepared by a freezing and freeze-drying method, which can significantly promote the encapsulation ratio of lauric acid in the pores of both aerogels and halloysite nanotube. Halloysite nanotube with high aspect ratio can improve the compressive strength of the aerogels and shape stability of the composite phase change materials, while reduced graphene oxide can reinforce the thermal conductivity and light absorption ability. After encapsulation of lauric acid, the halloysite/poly(vinyl alcohol) 9:1 and halloysite/poly(vinyl alcohol)/reduced graphene oxide 9:1 phase change composites demonstrate extraordinarily high latent heat of 195.4 J/g and 197.0 J/g, respectively, leading to high encapsulation ratios of 97.2 % and 98.1 % respectively, accompanied by good chemical and thermal stability over 300 thermal cycles. The thermal conductivity of lauric acid@halloysite/poly(vinyl alcohol)/reduced graphene oxide is remarkably elevated to 0.343 W/m∙K, exceeding 39.4 % that of pure lauric acid (0.246 W/m∙K). Besides, the lauric acid@halloysite/poly(vinyl alcohol)/reduced graphene oxide realizes a conspicuous solar-to-thermal conversion with solar absorption capacity of 95 % throughout the full spectrum of solar light. The marvelous improvement in the solar-to-thermal conversion efficiency can be attributed to thermally conductive interconnected network of halloysite nanotube and reduced graphene oxide. Thus, lauric acid@halloysite/poly(vinyl alcohol)/reduced graphene oxide and lauric acid@halloysite/poly(vinyl alcohol) are tentatively used in the catalytic hydrolysis of ammonia borane, and they can efficiently harvest, convert and store solar energy in the form of thermal energy and release it for the reaction, which obviously accelerates the extent of reaction with turnover frequency increasing from 29.50 (molH2/molcatalyst·min) at 25 °C to 59.18 and 41.74 (molH2/molcatalyst·min) under the heating of solar energy stored lauric acid@halloysite/poly(vinyl alcohol)/reduced graphene oxide and lauric acid@halloysite/poly(vinyl alcohol), respectively. This work paves a way for fabricating halloysite-based aerogel and composite phase change materials for thermal/solar energy saving application.

Numerical study on the thermal performance of foam-metal composite phase change material in different force fields

To make a better application of phase change material (PCM) in the thermal management of aerospace systems, this paper investigates effects of the variation of foam-metal pore structure on the thermal performance of composite PCM (CPCM) subjected to different force fields. A two-dimensional numerical model based on the enthalpy-porosity method and the two-temperature energy equation is developed and verified with the experimental data. The thermal behavior of CPCM with different porosities (ω = 20 PPI, ε = 0.91, 0.93, 0.95 and 0.97) and different pore densities (ε = 0.95, ω = 10, 20, 40 and 80 PPI) are investigated under centrifugal acceleration conditions of 0, 5 and -5 g, respectively. A novel index of "end-state isobars" is introduced to describe the melting process of CPCM. The results show that the isotherms of CPCM liquid phase evolve gradually towards the interface parallel to end-state isobars in all conditions. At 0 g, decreasing the porosity effectively improves the thermal conduction of CPCM and slows down the approaching of the isotherms to the end-state isobars. Similarly, increasing the pore density significantly weakens the natural convection of liquid PCM and can also slows down the approaching isotherms to the end-state isobars. At 5 g, the isotherms can match exactly with the end-state isobars, after which the heat transfer process mainly depends on conductive. And decreasing the porosity can significantly improve the thermal performance of CPCM, while adjusting the pore density has almost no effect. At -5 g, the natural convection strength of CPCM is enhanced, changing porosity has limited effect on the heat transfer performance of CPCM, while decreasing pore density can significantly enhance the heat transfer performance. The results may provide some valuable reference for the evaluation and design of latent heat thermal energy storage (LHTES) system suitable to the aerospace field.

Comparative study for photovoltaic cooling using metal mesh inserted eutectic phase change material enclosure

Phase change material (PCM) is a predominant storage material that enables a higher cooling effect over sensible heat storage materials without the assistance of working fluid. In this study, novel PCM infused finned, and mesh finned containers are developed to help cooling photovoltaic (PV) in operation by reducing the PCM conduction resistance. The designed container is integrated underneath the back surface of the PV module and experimented under controlled weather conditions (indoor). Fins are attached behind the PCM container without any intermediate layer favors transferring the heat from the top to the bottom fin surface as a single unit. The main benefit of a PCM-infused fin container enhances the PCM liquid flow movement throughout the finned morphology and the heat dissipation rate increases between the finned PCM container and its surroundings. Moreover, incorporating metal mesh inside the PCM container resulting to the control of the conduction barrier and increased the heat transfer rate. It is found that metal mesh based finned PCM container shows an excellent performance enhancement between 85th and 150th minutes with a peak cooling of 2.20% and corresponding to the electrical power and energy productions of 2.01% and 2.71%, respectively compared to finned PCM container. The statistical approach on finned and mesh finned PCM containers shows that ambient temperature has a strong positive correlation with the temperature rise in photovoltaic resulting in performance degradation. Furthermore, it is recommended that the developed PCM containers are suitable for tropical climatic conditions to improve the PV power output.

Industrial-scale for hydrogen charging in activated carbon (AX-21)-phase change material-nano-oxides systems

As a plausible solution for the issue of heat management during hydrogen adsorption on the activated carbon bed, in the present paper, the effects of different metal oxides nanoparticles (MgO, TiO2, CuO, or ZnO), scattered into a phase change material (PCM), have been investigated over the adsorption and dormancy phases in a large-scale bottle. This study has been conducted using Fluent software, in which a computational fluid dynamics (CFD) model (based on finite volume simulations) was implemented. This model has been validated via the experimental and theoretical results available in literature. Throughout the duration of the charging process, it has been found that the presence of nanoparticles in PCM body does not affect the thermal performance of the solid bed of activated carbon,. However, the melt fraction of PCM is steeply increased to 20 % in the range ~ 0–1300 s, whereas over 1300 s, the melting process of paraffin is amortized until the end of the dormancy phase (attaining ~ 30–35 % of liquid PCM). This trend is observed either in the presence or in the absence of metal oxides, where 16 % of enhancement in the liquid fraction of PCM is retrieved in the presence of nanoparticles (5 %) at the end of the dormancy phase (10,000 s). As a result, The nano-PCM system could be a proposed pathway for recovering the heat generated from the H2 adsorption and then replacing the fluid cooling system (cost). However, it was recommended that future research works should be focused on the improvement of the solid bed thermal conductivity in addition to the enhancement of the reactor geometry via new innovative solution pathways.

Experimental and numerical investigation of melting and solidification enhancement using Fibonacci-inspired fins in a latent thermal energy storage unit

The major challenge with phase change materials (PCMs) is their low thermal conductivity, eventuating long melting (charging) and solidification (discharging) times in latent thermal energy storage (LTES) units. Using extended surfaces (fins) is a popular method to resulve this issue, with recent developments in novel designs such as tree-like and fractal fins. The complex fin configurations improve the conduction while decreasing the natural convection effects by introducing additional shear stress to the melted PCM. The current work proposes a new fin design based on the Fibonacci sequence in a vertical LTES unit to improve the charging/discharging characteristic. The finned geometry is manufactured out of a solid block of aluminum using the wire-cutting technique. Based on the volume expansion method, an experimental setup is designed to observe the charging/discharging behavior. The PCM under study is RT42 and its density, volumetric thermal expansion coefficient and solid-state thermal conductivity are measured in house. Water is the chosen heat transfer fluid (HTF) set to a constant mass flow rate of about 99 kg/h and 96 kg/h for the melting and solidification processes, respectively. The water charging temperature is 61.5 °C while the water discharge temperature is 21.5 °C. A numerical model based on the enthalpy-porosity method is implemented to investigate the physics behind melting/solidification. A careful investigation of the mushy zone constant is performed based on comparing the experimental and numerical results for melting and solidification. The average liquid PCM velocity on the melt front is studied to evaluate the natural convection behavior. The effects of secondary flows and mixing on the melting process in the new geometry are studied by investigating the liquid PCM flow behavior during the charging. The proposed fin performed 20% better in total melting time than longitudinal fins by introducing more dispersed natural convection dominated regions. The reduction of 45% in solidification time is also established for the novel fin.

Performance analysis of PCM melting in a fin-assisted thermal energy storage system – A numerical study

The study attempts to present the melting phenomena in a Latent Heat Thermal Storage System (LHTSS) where ice is used as Phase Change Material (PCM) with fins incorporated to advance the thermal performance. The PCM-based storage system finds vast potential in addressing the imbalance between energy supply and demand. Computations are carried out to find the optimum fin number to be incorporated in Heat Transfer Fluid (HTF) tube for improved heat transfer and minimum melting time. The effect of incorporating optimum fin number on different influential parameters such as HTF tube arrangement, diameter, and temperature on charging performance is evaluated. The physical phenomena occurring due to increased fin number is also explained. Criteria such as liquid fraction, mean temperature, heat transfer rate, and heat transfer coefficient are used to compare the system's performance under varying parameters. As the number of fins is augmented from 4 to 15, the generated liquid PCM is found to increase by 34.69% followed by a declination rate of 9.03% on further increment in the numbers. Geometrical alteration in the HTF tube arrangement from inline to staggered results in a better melting performance. Considering the HTF tube temperature parameter, it is found that 280 K HTF tube produces 2.08 times more liquid PCM as compared to 275 K case. Increasing HTF tube diameter is found to enhance the charging process with 20 mm diameter HTF tube system generating 2.68 times more liquid PCM as compared to that of 5 mm HTF tube.

A comprehensive investigation of PCM based annular thermoelectric generator for energy recovery: Energy conversion characteristics and performance evaluation

Annular thermoelectric generators (ATEG) are increasingly attracting attention and are pivotal in thermal energy recovery due to their unique characteristics, which can be perfectly adapted to cylindrical heat sources. Considering the efficient thermal management and power generation of thermoelectric generator (TEG), phase change material (PCM) can be integrated with the cold side of TEG as a favourable cooling medium to meet its functional requirements. However, previous studies have focused on the intrinsic connection between flat-plat TEG and PCM, while the impact of PCM on ATEG has not been systematically explored. In the present study, an annular thermoelectric generator with PCM (ATEG-PCM) under a pulsed heat source is proposed, and its dynamic characteristics and energy distribution are evaluated. The effects of PCM parameters such as height, latent heat and melting temperature are comprehensively explored from multi-index, including PCM temperature, liquid fraction, temperature difference, output power, energy and exergy efficiencies. Furthermore, a comparative investigation of ATEG-PCM, PCM-ATEG where PCM is applied on the hot side, and ATEG without PCM is further carried out to clarify the coupled mechanism of PCM on thermal management and power generation enhancement of ATEG. The results indicate that the energy efficiency of ATEG-PCM has saturated at PCM height of 10 mm to 12 mm, while the exergy efficiency merely slightly increases. Especially, the PCM melting temperature merely affects the time at which PCM initiates to change from solid state to liquid state, without affecting the total energy efficiency of ATEG-PCM. Furthermore, the comparison analysis determines that ATEG-PCM deserves more attention, judging by thermal management and power generation. This work not only contributes to the understanding of the coupling mechanisms between PCM and ATEG but also provides a research direction for energy recovery in PCM based ATEG hybrid system.

Thermophysical Characterization of Paraffins versus Temperature for Thermal Energy Storage

Latent heat storage systems (LHSS), using solid–liquid phase change materials (PCMs), are attracting growing interest in many applications. The determination of the thermophysical properties of PCMs is crucial for selecting the appropriate material for an LHSS and for predicting the thermal behavior of the PCM. In this context, the thermophysical characterization of four paraffins (RT21, RT27, RT35HC, RT50) at different temperatures, including the solid and liquid phases, is conducted in this investigation. This work is part of a strategic technological brick in the CERTES laboratory of the Paris Est University to build a database for phase change material properties. It contains the measurements of the thermophysical, optical and mechanical properties. It will serve as input for the numerical simulations to study the behavior of PCMs in LHSS. The temperatures and the latent heats of the phase transitions as well as the thermal dependence of the specific heat of the paraffins were evaluated by differential scanning calorimetry (DSC). In addition, the DSC measurements under successive thermal cycles revealed good reliability of the paraffins. Thermogravimetric analysis (TGA) was performed, and the results highlighted the thermal stability of the paraffins. Moreover, the evolutions of the thermal conductivities and diffusivities with temperature were measured simultaneously using the hot disk method. A discontinuity of the thermal conductivities was observed near the melting temperatures. Furthermore, the measurements of the densities of the paraffins at different temperatures were carried out. The volume changes and the coefficients of thermal expansion were assessed. The obtained outcomes of this study were compared with the available bibliographical data.

Thermal performance of cold thermal energy storage system with fin and fin–foam structures

The heat transfer performance of most cold thermal energy storage (CTES) devices is limited by the low thermal conductivity of phase change materials (PCMs) and the increase in the thickness of PCMs. A comparative work was performed to explore the heat transfer performance of CTES systems with a fin structure (Fin-CTES) and a fin–foam structure (Fin–foam-CTES). The heat transfer performance, temperature distribution, and thermal effectiveness of Fin-CTES and Fin–foam-CTES at different inlet temperatures and volume flow rates of heat transfer fluid were investigated and compared. Results demonstrated that the overall heat transfer performance of Fin–foam-CTES is better than that of Fin-CTES. However, compared with the PCM in Fin-CTES, that in Fin–foam-CTES has a greater degree of supercooling, reaching 4.35 °C at the maximum. In the discharging (melting) process, Fin-CTES and Fin–foam-CTES have almost similar heat transfer effectiveness, in which the maximum difference is only 0.0107. That is, the enhanced heat transfer effect of the natural convection of the liquid PCM and the metal foam is basically the same during the discharging process.

Developing ternary composite phase change materials with two different phase change temperatures for battery thermal management

Paraffin wax (PW), as a phase change material (PCM), with high latent heat, is likely to be used in battery thermal management. However, the application of PW is remarkably limited due to its low thermal conductivity, poor mechanical properties, and easy leakage after melting. Here, we prepared a novel ternary composite phase change material (CPCM) to eliminate melt leakage with high thermal conductivity, stable morphology, and two different phase change temperatures. The step cooling data confirmed that when the proportions of myristic acid (MA), palmitic acid (PA), and PW are 3:1:4, there are two phase transition points at 35.88 ℃ and 46.26 ℃, respectively. The addition of short carbon fiber (SCF) and carbon black (CB) with different particle sizes significantly improved the thermal conductivity of the PCM up to 8.7 W/mK. The addition of silicone rubber (SR) film not only avoids the liquid PCM leakage but also improves its mechanical properties. At the highest discharge rate, the maximum temperature of a large capacity square terpolymer lithium battery is 47.03 ℃ due to excellent thermos conductivity. Furthermore, the ternary CPCM does not melt completely at the end of discharge. Compared with the CPCM with single phase transition temperature, the two different phase transition temperatures have excellent balanced performance. After two phase change temperature controlling processes, the rise of battery surface temperature is effectively delayed, and the working time of the CPCM is prolonged. Hence, the developed CPCM is more suitable for the battery thermal management system (BTMS).

Investigation of the characteristics and mechanisms of contact melting and float melting phenomena inside a sphere

In recent decades, unconstrained melting processes with high heat-transfer rates have attracted significant interest. This study provides an in-depth investigation of the characteristics and mechanisms of two unconstrained melting phenomena (contact melting and float melting modes) of n-eicosane inside a sphere subjected to a non-isothermal wall temperature. The effects of the heating time, initial temperature, and heating temperature are studied using an improved image processing method. Quantitative and qualitative comparisons with the two melting modes demonstrate that contact melting within the sphere occurs at a higher rate (up to 2.97%) than float melting. This is because of the long-term contact state of the solid phase change material (PCM) and low thermal resistance across the bottom thin liquid PCM layer. A float melting phenomenon occurs during the melting process is a random event depending on whether the solid PCM can reach the state of force equilibrium during the initial unconstrained melting process. Due to the free motion of the solid PCM and random movement of the floating bubbles, the probability of occurrence of the contact melting mode is greater than that of the float melting mode with a maximum probability of only 46.66%. Finally, dimensional analysis of the experimental data was performed and presented with an overall uncertainty below 15%. The findings can contribute to a better understanding of the float melting and spark the interest of more researchers to further explore the unconstrained melting process.

Numerical simulation study of the effect of mechanical vibration on heat transfer in a six-fin latent heat thermal energy storage unit

The optimization of heat transfer in latent heat thermal energy storage units (LHTES) has received a lot of research during the past decade, and the use of fins to enhance heat transfer in phase change materials (PCM) is one of the efficient ways. However, the existing studies do not consider the influence of mechanical vibration which widely exists in LHTES. To fill the research gap in this important topic, a horizontal shell-and-tube six-fin latent heat thermal energy storage unit is investigated in this study, and the effects of mechanical vibration are investigated by numerically simulating the PCM charging process in LHTES using the Enthalpy-porosity technique. In this paper, the charging rate of PCM, variation of key parameters such as Nusselt number, temperature and liquid fraction are analyzed in detail under vibration conditions. And the following conclusions can be obtained. (1) Mechanical vibration can significantly increase the charging rate of PCM, under the condition of vibration amplitude of 10mm and frequency of 1Hz (the melting time of PCM is reduced by 46.6%). (2) The enhancement effect of mechanical vibration on the melting rate of PCM increases with the increase of amplitude and frequency, but the enhancement efficiency keeps decreasing. These observations result from that the mechanical vibration changes the velocity of the liquid PCM, so the forced convective heat transfer of the PCM is significantly enhanced. Furthermore, the melting process of PCM is sensitively affected by increasing the amplitude than by increasing the frequency. Increasing the amplitude or frequency alone (amplitude from 10mm to 40mm; frequency from 1Hz to 4Hz) can reduce the total melting time of PCM by 75% and 68.7%, respectively.

Flame-Retardant and Form-Stable Delignified Wood-Based Phase Change Composites with Superior Energy Storage Density and Reversible Thermochromic Properties for Visual Thermoregulation

The development of form-stable phase change materials (PCMs) with flame retardancy and the visual thermal storage process is crucial for their application in building energy conservation. Herein, an active phosphorus/ammonium-containing non-formaldehyde flame retardant (APA) was synthesized based on the natural compound phytic acid. Then, wood-based form-stable PCM composites (PTPCMs) with high energy storage density, excellent flame retardancy, and real-time and visual reversible thermochromic properties were successfully fabricated by impregnating the thermochromic compound into the APA-grafted delignified wood. The delignified wood well supports the solid–liquid PCMs and avoids their liquid leakage during phase transition due to the high surface tension and strong capillary effect. The differential scanning calorimetry (DSC) results showed that the PTPCMs possessed high thermal energy storage density (165.3–198.6 J/g) and reliable thermal stability. With the concentration of the flame-retardant APA increased, the peak heat release rate (pHRR) and total heat release (THR) of PTPCMs reduced noticeably, demonstrating the enhanced flame retardancy of PTPCMs. Moreover, PTPCM composites had good thermoregulation properties and the visualization of the phase transition process was made possible by the reversible thermochromic properties. In summary, the novel PTPCMs show tremendous application potential for efficient building energy conservation.

PCM-Impregnated Textile-Reinforced Cementitious Composite for Thermal Energy Storage

The growing global energy demand requires solutions that improve energy efficiency in all sectors. The civil construction sector is responsible for a large part of global energy consumption. In this context, phase change materials (PCMs) can be incorporated into construction materials to improve the energy efficiency of buildings. The purpose of this study was to incorporate a PCM to jute fabric, applying it in civil construction as a reinforcement for cement matrices. In order to do that, a method of immersing jute fabric in liquid phase change material, and then coating it with a polymer, was proposed. Treated jute fabric was then used to produce a laminated composite with a cementitious matrix. Morphological, mechanical and chemical characterization of jute textiles was performed, as well as an analysis of the composites’ mechanical and thermal behavior. The results verified that jute textiles absorbed 102% PCM in weight, which was successfully contained in the capillary porosity of jute. The PCM was able to delay the composite’s temperature increase by up to 24 °C. It was concluded that this method can be used to incorporate PCM to natural textiles, producing composites with thermal energy storage properties.

Improving the melting performance of phase change material (PCM) in a latent heat thermal energy storage unit via a non-uniform arrangement of longitudinal fin

The application of latent heat thermal energy storage (LHTES) technology in solar energy utilization is greatly restricted by the low thermal conductivity of phase change material (PCM). This paper proposed a non-uniform arrangement of a longitudinal fin in a typical LHTES unit to improve the melting performance of PCM. Water is used as the heat transfer fluid (HTF) and paraffin (RT35) is selected as the PCM. A three-dimensional computational model is built to simulate the melting process of PCM, and its result is verified by experimental data. Firstly, the melting performance of PCM in the LHTES unit with four kinds of fin arrangements is comparatively studied, and its heat transfer mechanism is characterized via the maximum velocity of liquid PCM. In addition, the influences of HTF inlet temperature and flow rate, as well as heat transfer tube material on the complete melting time of three typical fin arrangements are also investigated. The results implied that the complete melting time of the non-uniform arrangement of the longitudinal fin reduces by 30.91% relative to the conventional longitudinal fin (Case 2). The results also revealed that the melting rate of PCM is related not only to the intensity of natural convection but also to the distribution of natural convection in the whole melting process.

Volumetric quantification of melting and solidification of phase change materials by in-situ X-ray computed tomography

Solid–liquid phase transitions in phase change materials (PCM) usually exhibit a complex dynamics, which critically determines the performance of latent heat thermal energy storage systems (LHTES). Experimental approaches enabling to track the dynamics of the entire PCM solid–liquid phase transition are thus crucial to provide relevant data for PCM material development and to validate PCM-models used to design efficient LHTES. In this work, we show how in-situ dynamic X-ray computed tomography (XCT) can be used to track the dynamics of the solid–liquid phase transition in PCMs. The method based on time-lapse XCT is illustrated based on data collected for two PCMs (ice/water and calcium chloride hexahydrate) during melting and solidification processes, respectively. Key enabler of the method is the density difference between solid and liquid PCM, which facilitates a clear identification of the solid and liquid PCM phases and, thus, tracking their spatial evolution in time. Analysis of the transient liquid fraction curves reveals a volumetric melting rate of 0.55 (% vol)/min for ice with a total melting time of 165 min, whereas calcium chloride hexahydrate undergoes a partial solidification at −0.30 (% vol)/min, with an overall volumetric shrinkage of 12.7 %. Furthermore, an image-based approach to quantify the time-dependent liquid volume fraction curve from the sequences of XCT imaging data, is presented. The extracted liquid volume fraction curves capture the entire dynamics of the solid–liquid phase transition and can either be directly inserted in the mass and energy balance equations of currently existing PCM models to predict LHTES performance or used for PCM-models validation.

Fe3O4-Functionalized κ-Carrageenan/Melanin Hybrid Aerogel-Supported Form-Stable Phase-Change Composites with Excellent Solar/Magnetic–Thermal Conversion Efficiency and Enhanced Thermal Conductivity

Impregnating organic phase-change materials (PCMs) into biomass-derived aerogels is regarded as one of the most effective and accessible approach to address the liquid leakage issues of solid–liquid PCMs. However, the inefficient solar–thermal conversion and low thermal conductivity still restrict the large-scaled applications of organic PCMs in solar utilization fields. Herein, novel form-stable PCM composites (CMPCM-Fe) with enhanced thermal conductivity and excellent solar- and magnetic-driven thermal energy conversion and storage efficiency were fabricated by impregnating n-docosane into Fe3O4-functionalized κ-carrageenan/melanin hybrid aerogels (CMA-Fe) through vacuum impregnation. CMA-Fe effectively supported n-docosane and prevented the leakage issue during the phase transition process owing to its strong surface tension and capillary force. CMPCM-Fe exhibited high encapsulated efficiency (88.9–94.6%), satisfactory thermal storage capacity (229.1–246.9 J/g), and excellent reversible stability. The introduction of Fe3O4 nanoparticles enhanced the thermal conductivity (55.3% increased) and solar–thermal conversion efficiency (up to 93.5%) of CMPCM-Fe and endowed it with excellent magnetic–thermal conversion capacity under an alternating magnetic field. The synthesized CMPCM-Fe possesses broad application prospect in mutiresponse thermal management.

Melting Processes of Phase Change Material in Sidewall-Heated Cavity

Melting processes of phase change material (PCM) confined in a rectangular cavity with an isothermal vertical wall are investigated to quantify the transition criterion between different melting regimes. A series of numerical simulations are conducted via the phase-change lattice Boltzmann method, and the results show that the temperature field in the liquid PCM region changes from the structure with two thermal boundary layers to the structure with two thermal boundary layers plus a convection region. Moreover, the results also indicate that the heat transfer mechanism undergoes a transition from conduction to convection when the relative thickness between the convention region and the thermal boundary reaches a critical value. This value (transition criterion) can be quantified by the critical melted volume fraction, and its dependence on Rayleigh number, Prandtl number, and aspect ratio of cavity is theoretically derived in this study. Then, based on the transition criterion, a piecewise correlation of melted volume fraction is proposed, which considers the effect of different melting regimes and is proven to predict the literature’s result.

Experimental study of minimum - temperature hydrated salt latent heat thermal energy storage with sodium acetate trihydrate as phase change materials

There’s a lot of hope for phase change material (PCM) in applications like sustainable energy generation and retrieval of heat loss. Latent heat thermal energy storage (LHTES) systems containing hydrated salt (HS) at minimum-temperature have been the topic of much study, particularly with regards to their thermal behavior and charging-discharging properties. The PCM was prepared by adding sodium acetate trihydrate (SAT), a nucleation agent, and a thickness agent to the test tube. We monitored PCM’s temperature behavior and analyzed its thermal characteristics. Natural convection was the dominant way of heat transmission while the phase change material temperature was over the fusion threshold, whereas conduction was the dominant mode when liquid phase change material formed during the phase transition progression. Heat storage and release efficiency as a function of tube diameter and flow rate was analyzed. Internal stainless-steel fins and aluminium fins of varying thicknesses were added to the tube to increase heat transmission. The shape of the storing tube and fins was shown to have a significant impact on the heat transmission among the thermal fluid and the phase change material. Charging and discharging duration may be cut by 28 % and 25 %, respectively, because to the revised fins shape. Our findings from this study can serve as an experimental foundation for using the minimum-temperature hydrated salt LHTES system.