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Although molten salt reactors and thermal storage systems are attracting increasing interest, our understanding of the physicochemical properties of molten salts is still incomplete. This is largely due to the difficulty of conducting experiments under extreme temperatures with strict control of impurities and corrosion. Ab initio calculations, machine-learned force fields, and classical molecular dynamics have helped to alleviate some of these issues. However, discrepancies between experimental and theoretical computations of the thermal conductivity of fluoride molten salts have become of increasing concern. In this paper, we present a modernized method for training a transferable equivariant graph neural network force fields to model a simple fluoride molten salt system, LiF–NaF, using minimal ab initio calculations. Using this transferable machine-learned force field, the thermal conductivity as well as various other functions of LiF–NaF were computed at various chemical temperatures and ratios in order to gain new insights into the limitations and behaviors of molten salts in relation to their thermal conductivity. Results show discrepancies between experimental and theoretical computations of the thermal conductivity as a function of temperature but good agreement between experimental and theoretical computations of the thermal conductivity as a function of ratio. Secondary results show compelling agreement of a machine-learned force field with first-principles computations and the ability to interpolate and extrapolate various chemical ratios. [ABSTRACT FROM AUTHOR]

Utilizing thermochemical reactions for thermal energy storage and solar fuel production has been an emerging research topic. Thermal transport properties of the materials are an important parameter that can determine the kinetics and efficiency of thermochemical reactions. With the increasing number of new thermochemical materials (TCMs); however, there is a lack of reliable techniques to monitor the thermal transport property of the materials and their changes as a function of reactions in real time. In this work, we report the in situ monitoring of thermochemical reactions using modulated photothermal radiometry (MPR). The thermal conductivities of two TCMs, namely, calcium hydroxide (Ca(OH)2) and Ba0.15Sr0.85FeO3−δ (BSF1585), were measured as a function of temperature and time using the MPR technique. The measured thermal conductivities were correlated to the reaction. The work has two significant contributions to the research communities. First, it provides a non-invasive diagnostic tool for monitoring the thermal transport properties of TCMs that can potentially be a high-throughput measurement technique conducive to optimizing TCMs, reactors, and related thermal systems. Second, for TCMs that show observable changes in thermal transport properties, a correlation between the measured thermal conductivity and the conversion fraction of the reaction can be established for monitoring the reaction kinetics based on thermal characterization. [ABSTRACT FROM AUTHOR]

The hierarchical three-dimensional porous structure MHP is constructed by assembling polyporre (PPy) modified halloysite (HNT/PPy) into the pores of melamine formaldehyde (MF) sponge for encapsulation of phase change materials (PCMs). The composite PCMs display unexceptionable leakage resistance, good solar-thermal conversion and storage as well as excellent solar-thermal-electric conversion performance, thus showing great potential for solar energy utilization. [Display omitted] • HNT/PPy was filled into MF to construct hierarchical 3D porous structure MHP. • MHP exhibits good stability and high encapsulation capability for PEG. • PEG@MHP shows good photothermal conversion, thermal storage and thermal stability. • PEG@MHP achieves efficient voltage and current output. Exploiting inexpensive composite phase change materials (PCMs) with comprehensive characteristics of high encapsulation efficiency, good leakage resistance, strong flexibility, high heat conductivity, and powerful light absorption is considerably imperative for their solar-thermal and solar-thermal-electric conversion. Herein, polypyrrole (PPy) modified halloysite (HNT/PPy) was assembled into the pores of melamine formaldehyde (MF) sponge to construct hierarchical porous structure (MHP), in which PPy serves as light absorber and heat conducting agent to consolidate the light absorption and thermal conductivity, while the interwoven HNT in MF not only acts as carrier to provide sufficient space for guaranteeing more PCMs' encapsulation, but also dramatically narrows MF's pore size and prevents PCMs' leakage. As expected, the MHP can encapsulate as high as 95 wt% of polyethylene glycol (PEG) with extremely high latent heat of 177.8 J g−1 (PEG@MHP). The rich hydroxyl groups on PEG, PVA and HNT form strong hydrogen bond interaction, effectively improving the leakage-proof performance of PEG@MHP. Especially, PEG@MHP with 82 wt% encapsulation ratio (PEG@MHP-82) demonstrates unexceptionable leakage resistance (negligible leakage at 100 °C), strong light absorption (97 %), good photothermal conversion efficiency (90.36 %), and high thermal conductivity (0.235 W m−1 K−1). Except that, the solar-thermal-electric (STE) conversion system assembled with PEG@MHP-82 enables efficient voltage and current outputs of 587 mV and 83.3 mA respectively under 3 kW m−2 with heat dissipation in water. Encouragingly, the voltage output still achieves 154.7 mV under actual outdoor illumination (0.984 kW m−2). This work provides a simple method to efficiently encapsulate PCMs for realizing high-efficiency solar-thermal and solar-thermal-electric conversion. [ABSTRACT FROM AUTHOR]

Micro-nanocavity graphene/paraffin nanocomposites (MNGPNs) are emerging as promising phase change materials for passive thermal management in electronics, utilizing the superior thermal conductivity of graphene in conjunction with the excellent heat storage capacity of paraffin. However, current assessments of MNGPNs thermal management performance are primarily conducted under laboratory static conditions, which do not fully represent the complex overload environments encountered in practical applications. In this study, we conducted strain freezing experiments using a split Hopkinson pressure bar and performed recovery analysis to investigate the influence of dynamic loading on thermal behavior through postmortem microstructural characterizations. Our findings reveal significant thermodynamic coupling effects in the in-plane direction, while coupling effects in the out-of-plane direction were less apparent. Specifically, the increase in internal thermal resistance under impact loading, due to the cracking, shedding, and directional changes in the graphene structure, diminishes the heat transfer capacity of MNGPNs in the in-plane direction. Alternations in interfacial thermal resistance caused by the layer compression and shedding affect the out-of-plane heat transfer capacity. Furthermore, the thermal behavior of MNGPNs was validated through heat dissipation experiments. This work provides valuable insights for the practical thermal management applications of MNGPNs, highlighting their performance from a dynamic perspective. [ABSTRACT FROM AUTHOR]

The development of nanofluids (NFs) has significantly advanced the thermal performance of heat transfer fluids (HTFs) in heating and cooling applications. This review examines the synergistic effects of different nanoparticles (NPs)—including metallic, metallic oxide, and carbonaceous types—on the thermal conductivity (TC) and specific heat capacity (SHC) of base fluids like molecular, molten salts and ionic liquids. While adding NPs typically enhances TC and heat transfer, it can reduce SHC, posing challenges for energy storage and sustainable thermal management. Key factors such as NP composition, shape, size, concentration, and base fluid selection are analyzed to understand the mechanisms driving these improvements. The review also emphasizes the importance of interfacial interactions and proper NP dispersion for fluid stability. Strategies like optimizing NP formulations and utilizing solid–solid phase transitions are proposed to enhance both TC and SHC without significantly increasing viscosity, a common drawback in NFs. By balancing these properties, NFs hold great potential for renewable energy systems, particularly in improving energy storage efficiency. The review also outlines future research directions to overcome current challenges and expand the application of NFs in sustainable energy solutions, contributing to reduced carbon emissions. [ABSTRACT FROM AUTHOR]

The use of advanced thermal storage materials, such as phase change materials (PCMs), offers a practical approach to reducing energy consumption in buildings while maintaining comfortable indoor temperatures. This work employs EnergyPlus to simulate the energy consumption of residential homes equipped with paraffin-based PCMs in Southern California, a region that experiences extremely high summer temperatures and significant day–night temperature variations. Two computational methods, the basic method and the hysteresis method, are employed. The effect of position, melting point, thickness, and thermal conductivity of PCMs on the energy savings rate in buildings is systematically investigated. The results show that the optimized melting point of PCM for Riverside and Palm Springs falls within the range of 19 to 21 °C. As thermal conductivity increases from 0.2 W m−1 K−1 to 3 W m−1 K−1, energy consumption in Riverside decreases by about 5%, whereas in Palm Springs, with its hotter summer temperatures, energy consumption increases. The optimal parameters yielded a total annual energy savings rate of 35.24% in Riverside and 18.52% in Palm Springs using the basic method and 35.47% in Riverside and 22.13% in Palm Springs using the hysteresis method. Under natural ventilation conditions, PCMs can reduce indoor day–night temperature differences in summer to 2.4 °C and 2.2 °C in Riverside, depending on the method used, compared to a 7 °C temperature difference without PCMs. Even without air conditioning, PCMs effectively maintain indoor temperatures within a comfortable range. This work demonstrates that optimizing PCMs in building design can significantly enhance energy efficiency and thermal comfort, providing a sustainable solution for reducing energy demands in residential settings. [ABSTRACT FROM AUTHOR]

Chloride salt is the most suitable heat transfer and storage medium for the next generation concentrated solar power generation, but its low thermal properties limit its large-scale application. Doping nanoparticles to form nanofluids is an important way to enhance the thermal properties of chloride salt. In this paper, molecular dynamics method is used to investigate the thermal properties of SiO 2 /(LiCl-KCl) nanofluids such as density, viscosity and thermal conductivity. Furthermore, the underlying strengthening mechanisms of nanoparticles on thermal properties of molten salt are also explored from the perspective of microstructure, energy and compress interface layers. The results show that the doped SiO 2 nanoparticles enhance the density, viscosity and thermal conductivity of molten salt. When the doping amount of SiO 2 nanoparticles is 6 wt%, the density, viscosity and thermal conductivity increase by an average of 1.22 %, 17.21 % and 6.30 %, respectively. The doped nanoparticles enhance the association between anions and cations, increase the collision frequency between ions and build a channel for heat transfer between nanoparticles and base salt ions, but weaken the diffusion ability of molten salt. [ABSTRACT FROM AUTHOR]

Phase change materials with excellent thermal energy storage property displayed great potential application in many fields, such as lithium battery thermal management, energy saving building and waste heat utilization. In this paper, a novel composite phase change material of Ag nanowires modified expanded graphite/lauric-myristic-palmitic acid (AgNWs@EG/LMP) with the function of photo/electro-thermal conversion property was prepared which the AgNWs@EG was acted as the matrix material and LMP was the phase change material. The composite exhibited high latent heat of 118.42 J/g at the phase change temperature of 33.62 °C with the LMP supporting ratio of 76.18%. The thermal conductivity of AgNWs@EG/LMP reached 4.23 W/(m∙K) which enhanced 1914% than that of LMP. The photo-thermal conversion efficiency reached 88.01% and the electro-thermal conversion efficiency was 65.4% with an input voltage of 1.5 V. Further results showed the composite AgNWs@EG/LMP possessed good chemical compatibility, good thermal stability and reliability. Therefore, the novel composite of AgNWs@EG/LMP with good thermal property and multi-energy conversion functions will process potential application in energy storage system and thermal management fields. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are important constituents for the storage of thermal energy available from the sun. It acts as a bridge between energy demand and supply while reducing the mismatch. Organic and inorganic constituents have been used for a long time for thermal energy storage applications. In recent years, the focus has been shifted to eutectics. A eutectic is a minimum melting substance of two or more constituents. It has the advantage of having a sharp melting temperature and possessing high volumetric heat storage density. The eutectics possess a wide range of temperatures and have the properties of all of their constituents. At present organic-organic, organic-inorganic, and organic-inorganic eutectics are widely studied. In the present paper, various eutectic PCMs for low and medium temperature ranges have been analyzed. Their thermophysical properties and thermal stability and reliability concerning thermal cycling have been thoroughly discussed. The melting temperature lies in the range of −23.50 °C to 80 °C and the latent heat of fusion can be as high as 280 kJ/kg. Thermal cycle tests of up to 30000 have been conducted by various research groups, but at least 300 melt/freeze cycles are recommended so that they can be stable for a year of application. The organic eutectic PCMs are found stable in terms of deviation in melting temperature with the maximum deviation in latent heat of fusion observed was ± 20 %. The inorganic eutectic PCMs are somewhat unstable having a large deviation in melting temperature and latent heat of fusion. The low thermal conductivity of organic eutectics can be eliminated with suitable nanoparticle additives. The leakage issue can be eliminated by providing shape stabilization to the PCMs. These PCMs are suitable for various photovoltaic/thermal, buildings, textiles, solar water heating, solar air heaters, and heat recovery systems applications. [ABSTRACT FROM AUTHOR]

This research reviews the stability of recently discovered phase change materials (PCMs) for use in absorption refrigeration within solar thermal storage systems. Incorporating PCMs into these systems offers a viable method for temperature control and energy storage, addressing the increasing demand for effective and sustainable cooling solutions. This study examines the chemical, thermal, and mechanical properties of various PCMs, including organic, inorganic, and eutectic substances, to evaluate their stability. Key characteristics influencing PCM stability include thermal, physical, and chemical properties, as well as high energy storage capacity, mass density, thermal conductivity, heat capacity, phase change enthalpy, and shape-stabilized structures. This review assesses the thermal stability of PCMs at the system level, considering factors such as confinement medium, heat transfer fluid, and optimal combinations. It provides a comprehensive analysis of experimental data on desirable PCMs, utilizing advanced selection processes, software enhancements, and operational temperature considerations, especially during periods without solar input. Moreover, the incorporation of nanoparticles enhances thermal performance during phase transitions, significantly improving system efficiency. The future scope of PCMs involves more research into their benefits and downsides, the examination of numerous choices, and an assessment of their energy efficiency and cost-effectiveness. [ABSTRACT FROM AUTHOR]

Bioinspired composites for thermal energy storage have gained much attention all over the world. Bioinspired structures have several advantages as the skeleton for preparing thermal energy storage materials, including preventing leakage and improving thermal conductivity. Phase change materials (PCMs) play an important role in the development of energy storage materials because of their stable chemical/thermal properties and high latent heat storage capacity. However, their applications have been compromised, owing to low thermal conductivity and leakage. The plant-derived scaffolds (i.e., wood-derived SiC/Carbon) in the composites can not only provide higher thermal conductivity but also prevent leakage. In this paper, we review recent progress in the preparation, microstructures, properties and applications of bioinspired composites for thermal energy storage. Two methods are generally used for producing bioinspired composites, including the direct introduction of biomass-derived templates and the imitation of biological structures templates. Some of the key technologies for introducing PCMs into templates involves melting, vacuum impregnation, physical mixing, etc. Continuous and orderly channels inside the skeleton can improve the overall thermal conductivity, and the thermal conductivity of composites with biomass-derived, porous, silicon carbide skeleton can reach as high as 116 W/m*K. In addition, the tightly aligned microporous structure can cover the PCM well, resulting in good leakage resistance after up to 2500 hot and cold cycles. Currently, bioinspired composites for thermal energy storage hold the greatest promise for large-scale applications in the fields of building energy conservation and solar energy conversion/storage. This review provides guidance on the preparation methods, performance improvements and applications for the future research strategies of bioinspired composites for thermal energy storage. [ABSTRACT FROM AUTHOR]

Thermal energy and its storage systems play an extensive role in day-to-day life. They store renewable energy and are capable of recovering generated heat from different systems. Storage of thermal energy can be classified into three types: sensible, latent and sorption heat storages. Thermal heat storages use different types of materials based on their capacity of heat storage, stability of duration and thermal conductivity. Various phase change materials (PCMs) that are suitable for thermal storage are reported. Low conversion ability limits their effectiveness. We reviewed some of the traditional materials synthesized recently that are used for thermal energy storage (TES). Recently developed TES materials exhibit high thermal conductivity, reduced super cooling and multiple phase change temperatures. Nano-enhanced PCMs produced an increase in thermal conductivity up to 32% with a reduction in latent heat by 32%. At this juncture, MXenes with high performance and extraordinary properties (thermal, mechanical, etc.) are of special significance. MXenes displayed an increased thermal conductivity up to 16% and 94% efficiency. In view of their structure and adaptability to be used in thermal storage systems, an attempt was made to review their role also in thermal storage applications. It is observed that MXenes highly impact storage and efficiency. Apart from MXenes, various types of PCMs along with their thermal characteristics are presented. Organic PCM's exhibit low melting point and high latent heat making them significant for TES. Organic PCM's are widely used in TES systems for consolidation and maintenance of alternative energy. However, leakage during phase transition limits their practical applications. [ABSTRACT FROM AUTHOR]

PW–EG composite phase change materials (CPCMs) with varying expanded graphite (EG) mass fractions were prepared by vacuum adsorption, using EG as the matrix and paraffin wax (PW) as the phase change material (PCM). The optimal addition amount of EG was determined to be 20 wt% based on the enthalpy change and leakage performance of the CPCMs. At this optimal composition, the thermal conductivity of CPCM enhanced significantly from 0.348 to 6.003 W/(m·K). SEM analysis revealed effective adsorption of PW within the pores of EG, reducing the leakage rate of PW to below 2.0%. The DSC results showed that the melting temperature and solidification temperature of CPCM were 36.3 °C and 40.80 °C, respectively, with the corresponding latent heat of 113.2 J/g and 106.6 J/g, respectively. FT‐IR and XRD results confirmed that the interactions of PW and EG were primarily due to capillary action, demonstrating excellent chemical compatibility. The TG test results showed that using EG may improve heat resistance of PW, increasing the heat resistance limit temperature from 110 to 142 °C. After 200 thermal cycles, the CPCM exhibited satisfactory thermal properties, excellent structural integrity, and thermal stability, which will provide a great potential of PCM for thermal energy storage applications. [ABSTRACT FROM AUTHOR]

Direct harvesting of abundant solar thermal energy within organic phase-change materials (PCMs) has emerged as a promising way to overcome the intermittency of renewable solar energy and pursue high-efficiency heating-related applications. Organic PCMs, however, generally suffer from several common shortcomings including melting-induced leakage, poor solar absorption, and low thermal conductivity. Compounding organic PCMs with single-component carbon materials faces the difficulty in achieving optimized comprehensive performance enhancement. Herein, this work reports the employment of hybrid expanded graphite (EG) and carbon nanotubes (CNTs) to simultaneously realize leakage-proofness, high solar absorptance, high thermal conductivity, and large latent heat storage capacity. The PCM composites were prepared by directly mixing commercial high-temperature paraffin (HPA) powders, EG, and CNTs, followed by subsequent mechanical compression molding. The HPA-EG composites loaded with 20 wt% of EG could effectively suppress melting-induced leakage. After further compounding with 1 wt% of CNTs, the form-stable HPA-EG20-CNT1 composites achieved an axial and in-plane thermal conductivity of 4.15 W/m K and 18.22 W/m K, and a melting enthalpy of 165.4 J/g, respectively. Through increasing the loading of CNTs to 10 wt% in the top thin layer, we further prepared double-layer HPA-EG-CNT composites, which have a high surface solar absorptance of 92.9% for the direct conversion of concentrated solar illumination into storable latent heat. The charged composites could be combined with a thermoelectric generator to release the stored latent heat and generate electricity, which could power up small electric devices such as light-emitting diodes. This work demonstrates the potential for employing hybrid fillers to optimize the thermophysical properties and solar thermal harvesting performances of organic PCMs. [ABSTRACT FROM AUTHOR]

Syntactic foams are lightweight porous composites obtained by the addition of hollow glass microspheres (HGMs) to a polymer matrix. This work experimentally and numerically investigates the thermal behavior of epoxy‐based syntactic foams with enhanced multifunctionality produced by incorporating microencapsulated phase change materials (PCMs) as functional fillers, providing thermal energy storage and temperature stabilization due to its large latent heat of melting. Foams are fabricated using varying ratios of HGMs (0–40 vol%) and PCM (0–40 vol%) to achieve tuned densities and thermal properties with a total filler content of up to 40 vol%. A one‐dimensional numerical heat transfer model based on the enthalpy method is presented to simulate the thermal behavior of these materials. The model accurately incorporates the specific heat and thermal conductivity of the foam components, as well as the latent heat absorption during PCM melting (up to 68 J/g). The model is experimentally validated by demonstrating good agreement with the measurements of transient temperature profiles during heating tests on the foam samples. The validated tool is then leveraged to model the thermal response of the foams under a sinusoidally varying heat source, similar to the possible real applicative scenarios. These results can help optimize foam compositions balancing energy storage density, heat transfer properties, and structural support for lightweight energy storage systems. Potential applications include high‐efficiency thermal management in battery packs, electronic cooling, solar energy storage, and sustainable temperature‐controlled buildings. Highlights: Foams with 0–40 vol% PCM and 0–40 vol% HGM show up to 68 J/g latent heat.1D numerical model accurately captures thermal conductivity and PCM phase change.Validated model simulates thermal response under sinusoidal heat, optimizing foam composition.Foams act as thermal reservoirs, maintaining up to 5°C lower surface temperatures than epoxy. [ABSTRACT FROM AUTHOR]

This study aims to optimize the phase change material (PCM) and fin structure, in order to improve the heat storage efficiency of the casing unit. Paraffin, lauric acid, and stearic acid were mixed with three organic PCMs. Once the total volume was constant, the volume fraction of the three PCMs was adjusted to prepare the mixed organic PCMs. An optimal combination was selected with the highest thermal conductivity. Then, Al2O3, Fe2O3, Fe, and Cu nanoparticles with different mass fractions were doped into the organic PCMs, in order to prepare a variety of composite phase change heat storage materials. The results show that four types of nano-Cu with different weight fractions (0.5%, 1%, 1.5%, and 2%) were selected as the additives to improve the thermal conductivity of the original PCM samples of 0.2% SDBS. The thermal conductivity values were 0.371, 0.373, 0.374, and 0.370 W/(m·K), respectively, which were 13.46%, 14.07%, 14.37%, and 13.15% higher than that of the sample without Cu nanoparticles, respectively. The composite PCM with 1.5% Cu nanoparticles shared the highest thermal conductivity of 0.374 W/(m·K), which was 14.37% higher than that of the sample without Cu nanoparticles. The typical fin structure of casing was summarized into four shapes: triangular, parallelogram, rectangular, and fan-shaped. The heat transfer performance of the four shapes was numerically simulated, according to the same working conditions: the volume ratio of the fin to the heat storage material, and the heat exchange edge length. It was found that the arc-shaped and straight fin were combined to achieve the high melting rate of the fan-shaped structure. The three-dimensional numerical simulation was carried out on the heat storage device of the fin structure using FLUENT software. Once the Ste number changed from 0.3 to 0.7, the melting time was reduced from 7 207 to 904 s, where the whole melting time was shortened by 6 303 s. Once the Ste number was 0.7, there was the maximum temperature difference between HTF and PCM. The natural convection was particularly intense to further accelerate the melting process of the heat storage unit. The relationship between melting time and Ste number was fitted by dimensionless quantity. The heat flux corresponded to the different Ste numbers. Once the Ste number was 0.3, the peak value of heat flux reached 155 W at the beginning of melting and then decreased gradually. The reason was that the HTF with the temperature difference between the initial and PCM entered the inner tube for heat exchange, and then the heat flux rate increased rapidly to the peak, due to the superior thermal conductivity of the steel pipe, while the HTF was continued to transfer the heat into the steel pipe, finally the heat loss occurred in the flow process, resulting in the heat flow rate gradually decreasing until the end of melting. The peak heat flow reached 436 W at a Ste number of 0.7, due to the large temperature difference between the HTF inlet temperature and the PCM. The findings can also provide a strong reference to improve the heat storage efficiency of phase change heat storage units. [ABSTRACT FROM AUTHOR]

Phase-change materials (PCMs) with three-dimensional thermally conductive skeletons show promise for thermal energy storage, but they have poor stability. Therefore, based on hydrogen bonding between graphene oxide and polyvinyl alcohol, a shape-stable thermally conductive graphene oxide/graphene nanoplates/polyvinyl alcohol (GO/GNP/PVAs) 3D porous skeleton was prepared by a simple vacuum freeze–drying method in this paper. To further improve the thermal conductivity of the GO/GNP/PVAs 3D porous skeleton, so carbonization is applied on it. After encapsulating polyethylene glycol (PEG) in the skeleton, a thermally conductive phase-change composite with good shape stability was obtained, even at a PEG loading as high as 96.1%. The carbonized C-GO/GNP/PVAs/PEG phase-change composites exhibited higher thermal conductivity (1.57 W m−1 K−1) than uncarbonized GO/GNP/PVAs/PEG phase-change composites (0.52 W m−1 K−1). This was mainly due to the low thermal conductivity GO annealing into high thermal conductivity reduced graphene oxide (rGO), which formed a conductive three-dimensional network. Meanwhile, the formation of a carbon skeleton by PVA chains after annealing also improved the thermal conductivity of the composites. The C-GO/GNP/PVAs/PEG phase-change composites also showed excellent solar-to-heat conversion properties. [ABSTRACT FROM AUTHOR]

This review presents a comprehensive comparative study on the thermal conductivity enhancement of molten nitrate salt when integrated with multi-walled carbon nanotubes (MWCNTS), expanded graphite, and graphene. Thermal conductivity is a crucial parameter in thermal energy storage systems and enhancing it can significantly improve the efficiency of such systems. The paper discusses the individual and synergistic effects of MNCNTS, Expanded graphite, and graphene on the thermal conductivity of Molten nitrate salt. The introduction provides a background on the importance of thermal conductivity in energy storage applications and the rationale behind using MNCNTS, expanded graphite, and graphene. The review then delves into detailed analyses of how each additive—MNCNTS, expanded graphite, and graphene—affects the thermal conductivity of Molten nitrate salt. MNCNTS are highlighted for their high thermal conductivity and structural stability, expanded graphite for its phase change properties and latent heat capacity, and graphene for its superior thermal properties and large surface area. Comparative results are discussed, showcasing the performance of each composite and identifying the most effective combinations. The paper summarizes the key findings, indicating that the hybrid incorporation of these materials can lead to significant improvements in thermal conductivity, thereby enhancing the overall performance of thermal energy storage systems. [ABSTRACT FROM AUTHOR]

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Lithium-ion batteries (LIBs) are progressing towards higher energy densities, extended lifespans, and improved safety. However, battery thermal management systems are facing increased demand owing to high-rate charging and discharging, dynamic operating conditions, and heightened thermal safety concerns. Therefore, this paper proposes a novel composite phase change material (CPCM) comprising Na2SO4-10H2O as the core phase change material (PCM) and expanded graphite as the thermal conductivity enhancer. The CPCM offers high latent heat, superior thermal conductivity, and a two-stage temperature control function for battery thermal management and safety. The optimal mass CPCM ratio, determined through comprehensive characterization and thermal property tests, resulted in a melting point of 29.05 C, latent heat of 183.7 J·g 1, and high thermal conductivity of 3.926 W·m 1·K 1. During normal LIB operations, the CPCM efficiently absorbs and transfers heat, reducing the peak LIB temperature from 66 to 34 C at 15 C ambient temperature during a 3.7C high-rate discharge. Under dynamic conditions, the peak temperatures across the three cycles were consistently controlled at 36.7, 36.4, and 35.8 C, respectively. In a thermal runaway state, the thermochemical heat storage of hydrated salt dehydration effectively slowed LIB temperature increase, delaying the time to reach 130 C by 187 s. Suppression of the temperature rise outside the CPCM, combined with an extended dehydration plateau of up to 320 s, prevented the occurrence and propagation of thermal runaway in the battery. [ABSTRACT FROM AUTHOR]

Solid–solid phase change materials (SSPCMs) are among the most promising candidates for thermal energy storage and management. Excellent shape stability, high heat storage capacity, and satisfying mechanical properties are essential for the practical applications of SSPCMs, yet giving PCMs these characteristics at the same time remains an unmet challenge. Herein, the synthesis of PEG‐PVEG copolymers is reported with various vinyl content using a synergistic catalysis strategy, leading to novel cross‐linked PEG‐based SSPCMs via a thiol‐ene photo‐crosslinking reaction. These PCMs exhibit excellent shape stability and remarkable energy storage capabilities with latent heat up to 128.3 J g−1. The materials exhibit exceptional thermal stability and retain their energy storage capacity after 500 heating‐cooling cycles. Notably, the materials show superior mechanical strength and excellent toughness. Furthermore, the latent heat enthalpy can be further improved to 146.8 J g−1 without erosion of shape stability by the encapsulation of PEG into present SSPCM. The enhancement of both thermal and electrical conductivities is also demonstrated by the phase change composites (PCCs) incorporating multi‐walled carbon nanotubes (MWCNTs). Overall, this study presents a convenient and feasible strategy for developing SSPCMs with excellent shape stability, high latent heat and satisfying mechanical properties for thermal management. [ABSTRACT FROM AUTHOR]

Guided by the goal of improving the heat transfer efficiency of geothermal cement, the development of high thermal conductivity fillers is urgently needed. Considering the drawbacks of carbon-based fillers in deteriorating the strength and fluidity of cement, this study proposes the use of green and low-cost deep eutectic solvents (DES) loaded with graphene oxide to form nanofluids (GONF) to improve the connection between graphene oxide and cement. The thermal conductivity and basic properties of GONF-cement under thermal storage conditions (60–100 °C, 0–36%NaCl) were reported, and the influence mechanism of nanofluids was analyzed. The following interesting conclusions were found: (1) The oxygen-containing functional groups on the surface of graphene oxide were connected to active sites of DES through the formation of the hydrogen bond network, forming thermal stable nanofluids. (2) Nanofluids was proven to be a low-cost (reduce material costs of graphene oxide by 90%) and effective material for enhancing the thermal conductivity and mechanical properties of geothermal cement while maintaining appropriate fluidity and low variation of density. (3) The synergistic mechanism between nanofluids and cement is due to the fact that nanofluids promotes hydration process by providing stable reaction sites, significantly reducing the porosity and pore size of cement. The dense structure enhances compressive strength and shortens the heat transfer path. This study enriches geothermal cementing technology and provides support for the low-cost application of graphene oxide in exploration engineering. [ABSTRACT FROM AUTHOR]

Molten salts are extensively used as high-temperature heat transfer media and thermal energy storage (TES) materials in concentrating solar power (CSP) plants. Molten salt corrosion is a critical factor influencing the safe operation of the system. This work comparatively summarizes various factors influencing molten salt corrosion, including temperature, impurities, alloy composition and gas atmosphere. Additionally, the corrosion mechanisms of nitrate, carbonate, chloride, and fluoride-based mixture salts are meticulously reviewed. The demand for high-temperature storage is indeed increasing, driven by the need for more efficient and sustainable energy solutions. High-temperature storage systems, particularly those utilizing phase change materials (PCMs) and molten salts, play a key role in enhancing energy efficiency and reducing carbon footprint. By improving the efficiency of energy storage and reducing the need for fossil fuels, high-temperature storage systems help decrease greenhouse gas emissions, contributing to the fight against global warming. The paper focused on enhancing the corrosion resistance of container materials in terms of improving PCM thermal conductivity and stability. [ABSTRACT FROM AUTHOR]

The utilization of graphene aerogel encapsulated phase change materials (PCMs) presents a promising strategy to achieve solar‐thermal energy conversion and storage. However, the self‐stacking effect and inherent lattice defects in graphene aerogel significantly restrict its overall performance in the encapsulation of PCMs. Herein, interfacially self‐assembled amino‐attapulgite/graphene hybrid aerogels (GNA) are prepared via inspired by the mortise‐tenon structure. Thanks to the structural regulation of the graphene aerogel by the amino‐attapulgite nanofibers, the hybrid aerogels establish a continuous heat transfer pathway inside and ensure stable encapsulation of PCMs. The solar‐driven shape‐stabilized composite PCMs (LA/GNAb) based on GNAb impregnated with lauric acid (LA), which achieves coordinated enhancement of the effective encapsulation rate for LA (93.1%), thermal conductivity (1.164 W m−1 K−1), and photothermal conversion capability (90.5%). Drawing upon the photothermal conversion and thermal storage properties of LA/GNAb, this study demonstrates its advanced applications in solar‐driven desalination and solar‐thermoelectric generation. The evaporator and generator with integrated LA/GNAb show a high evaporation rate of 2.13 kg m−2 h−1 and a stable power density of 1.57 W m−2 under 1‐sun irradiation, respectively, which can sustain additional operating time even under the dark. This work provides new insight into the design of multifunctional solar‐driven thermal interfacial materials. [ABSTRACT FROM AUTHOR]

Infrared emitters are highly desirable for applications in infrared imaging and stealth technology. Photothermal film emitters, which are driven by light, have garnered considerable interest due to their excellent photothermal properties and ease of fabrication. However, existing photothermal films often suffer from low photothermal conversion efficiency (PCE) and limited array scale. Here, a photothermal film emitter featuring a double‐S microbridge structure is presented, which comprehensively considering the PCE and frame rate. Initially, Si microbridges are fabricated within each microstructure to support the photothermal film. The pattern structure is then arranged into a double‐S configuration to manipulate the thermal conductivity. By optimizing the length and width of the double‐S pattern, high PCE and fast frame rates are achieved. The double‐S microbridge structure photothermal film emitter is fabricated with a 4‐inch diameter, forming an ultra‐large array with over 3000 × 3000 pixels. The absorption and photothermal conversion characteristics are studied, revealing a maximum temperature of 582.70 K and a highest PCE of 16.32%. Time‐dependent photothermal response demonstrated the emitter's rapid heat storage and release capabilities. Additionally, an infrared scene generator is realized. These results position the photothermal film emitter as a promising solution for infrared imaging and dynamic scene generation. [ABSTRACT FROM AUTHOR]

This study aims to assess the thermal performance of silica sand as a heat storage medium within a shell-and-tube sensible heat storage thermal energy system that operates using water as the heat transfer fluid. Two types of silica sand were analyzed, fine sand and coarse sand, to determine which was the best for heat transfer and storage. It was found that the fine sand, which had smaller particles compared to the coarse sand, enhanced the heat transfer in the system. The fine sand required 11.86 h to charge using the benchmark case and 17.58 h to discharge, whereas the coarse sand required 13.36 h to charge and 16.55 h to discharge. Methods of enhancement are also explored by comparing the system performance with the inclusion of four different configurations of copper fins to investigate against a benchmark case without fins in the system with fine sand. When equipped with four radial fins, the system demonstrated a significant enhancement, reducing charging and discharging times by 59.02% and 69.17%, respectively, compared to the baseline. Moreover, the system exhibited an even greater improvement with eight radial fins, cutting charging and discharging times by 63.74% and 78.5%, respectively, surpassing the improvements achieved with four radial fins. The ten annular fins decreased the charging time by 42.58% and the discharge by 62.4%, whereas the twenty annular fins decreased the charging by 56.24% and the discharging by 68.26% when compared to the baseline. [ABSTRACT FROM AUTHOR]

Expanded graphite (EG) based phase change material (PCM) has attracted significant concern in thermal management systems. In this paper, a series of composite PCMs composing of EG with different sizes (50, 80, and 100 mesh) as the substrate, and palmitic acid (PA) as the PCM, were prepared by vacuum impregnation method. The results shown that the size of EG particles effect the adsorption capacity of PA. The mass fraction of PA in PA/EG-50 reached 83.6% and the enthalpy of melting and solidification of PA/EG-50 are 160.13 J/g and 159.75 J/g, respectively. The thermal conductivity decreased slightly as the particle size of EG increased, and the thermal conductivity of PA/EG-100 is the highest of 4.86 W/(m·K). The TGA results show that all composite PCMs present good thermal stability below 200 °C. The electro-thermal conversion efficiency increased with the particle size of EG increasing, and the electro-thermal conversion efficiency of PA/EG-100 reached up to 91.39% under low-voltage conditions (1.9 V). These results throw light on the potential application of EG-based composite PCM, especially for the electro-thermal conversion. [ABSTRACT FROM AUTHOR]

This current work presents the experimental validation to improve the performance of solar thermal storage systems in solar thermal applications at intermittent, fluctuating and off-sunshine periods. This study investigates enhancing the performance of PCM, the blended composition of paraffin wax/glycerine in ratios of 75/25, 50/50 and 25/75 (weight in g), paraffin wax/iron oxide and paraffin wax/Copper oxide in different concentrations (x=0.05, 0.1, 0.5) were prepared by dry grinding and melt-mixing method. During the experimental results show higher thermal accumulation at a 75/25 paraffin wax/glycerine ratio in thermal energy storage. And also, the thermal conductivity was further improved when aluminium finned strips were immersed in the blend compositions. In investigations on dielectric constant of pure paraffin wax, paraffin wax/iron oxide and paraffin wax/copper oxide are compared. The result shows that thermal conductivity improved with the increasing concentration of the iron oxide and copper oxide, that is, paraffin wax/iron oxide (5/0.5) and paraffin wax/copper oxide (5/0.5) compared to the parent compound (paraffin wax). In addition, the moisture content of the studied samples was determined, showing 0.85% (pure paraffin wax), 7.5% (paraffin wax/glycerine), 4.509% (paraffin wax/iron oxide) and 0.927% (paraffin wax/copper oxide). [ABSTRACT FROM AUTHOR]

This study examined the thermal performance of Comfortboard23, a commercial gypsum board from Knauf infused with phase change material (PCM). Structural characterization using XRD and SEM confirmed the presence of microencapsulated PCM within the gypsum matrix. The study does not provide a direct comparison between Comfortboard23 and other PCM-integrated gypsum boards on the market. This is a limitation of the research. A comprehensive comparison would involve testing multiple products under identical conditions, and evaluating factors such as thermal performance, cost-effectiveness, durability, and ease of installation. Thermal characterization involved a novel low-scale thermal chamber to measure U-value, thermal conductivity, heat storage capacity, and dynamic thermal response. Results showed incorporating PCM decreased the U-value by 2% compared to standard gypsum boards. Additionally, PCM inclusion increased heat storage capacity by around 45% and improved dynamic thermal characteristics by decreasing thermal stability coefficient from 0.92 to 0.76 and increasing thermal lag from 0.27 to 0.49 h. The 45% increase in heat storage capacity of Comfortboard23 could lead to a 10–20% reduction in heating and cooling energy consumption, improved thermal comfort, and potential HVAC downsizing. Exact benefits depend on climate, building design, and occupancy patterns, necessitating further research in diverse real-world settings. The findings demonstrate Comfortboard23's potential for enhancing thermal energy storage in buildings, contributing to energy savings, improved thermal comfort, and reduced temperature fluctuations across varying daily temperatures. Overall, the study highlights the promise of Comfortboard23 as an energy-efficient PCM-integrated building material. [ABSTRACT FROM AUTHOR]

Under the background of vigorously promoting clean heating, the introduction of phase‐change energy storage technology into heating systems has become a new hot issue. In this study, a novel KAl(SO4)2·12H2O/expanded graphite (EG) shape‐stabilized composite phase‐change material (PCM), with a melting temperature of 91.6 °C, latent heat of 245.7 kJ kg−1, and high heat conductivity of 2.07 W m−1 K−1, is prepared to manufacture a PCM‐based module for space heating. This phase‐change electric heating module is developed, and its heat storage and release characteristics are investigated through experimental and numerical studies. The numerical model is validated by experimental results. In view of the numerical simulation, the structure of the module is optimized and its thermal performance is studied. Based on the optimized module, a peak‐valley time‐of‐use (TOU) electric heating module is finally proposed. It is revealed that the module exhibits good thermal performance and is capable of satisfying the indoor heating demand. The effective heat storage and release duration is 8.12 and 15.34 h, which can perfectly realize the operating mode under the "peak‐valley TOU electricity" mechanism. In this study, it is demonstrated that peak–valley electric energy storage heating devices have broad prospects in building space heating and provides reference for future application. [ABSTRACT FROM AUTHOR]

Flavored cigarettes are very popular among consumers. However, many essential oils in cigarettes are lost during storage, and the utilization rate of the essential oils during use is low. Therefore, effective packaging and stable sustained release are urgently needed. In this study, a composite electrospun stable nanofiber storage material was prepared for sustained release. Polyethylene glycol, which has good heat storage properties, was selected as the heat storage material to inhibit the release of essential materials during storage. Porous graphene with good thermal conductivity and a porous structure was selected as the heat conductive component to ensure rapid and uniform release. Polyethylene glycol/porous graphene polyvinyl alcohol-mint essential oil sustained-release composite electrospun nanofibers membrane was prepared by electrospinning, and the morphology, composition, thermal properties, and sustained-release properties were tested. The results showed that the composite electrospun nanofiber membrane reduced the loss of mint oil during storage and enabled the rapid release of mint oil at high temperatures. At room temperature, the retention rate of the mint oil was still more than 90% after 120 h, and at a high temperature (75°C) the retention rate was less than 20% after 10 min; that is, 80% of the essential oil material was released within 10 min. [ABSTRACT FROM AUTHOR]

Cordierite-mullite composite ceramics were prepared by solid-state method using Panzhihua low-grade Ti-rich clay, talc, and alumina. Influences of cordierite/mullite ratio, sintering temperature, and the chemical composition of clay on the phase composition, microstructure, physical properties, and thermal properties were investigated in detail. The results showed that the impurity oxides inside the Ti-rich clay had a great ability of forming liquid. Above 1300 °C, the reaction between TiO 2 of the clay and Al 2 O 3 produced stable Al 2 TiO 5 , which was conducive to decreasing the coefficient of thermal expansion (CTE). At 1300–1350 °C, the secondary mullitization caused the volumetric expansion, decreasing the bending strength and increasing the CTE. The optimum ratio of cordierite to mullite ranged from 90:10 to 80:20, and the sample fired at 1400 °C exhibited the lowest water absorption and porosity (0.64 % and 1.56 %, respectively), optimal bulk density, and bending strength (2.59 g cm−3 and 87.79 MPa), as well as better CTE, thermal conductivity, and thermal storage density (2.91 × 10−6 °C−1, 4.11 W/(m⋅K) (30 °C), and 1181 kJ kg−1, respectively). Compared with the reported values of cordierite-based thermal storage ceramics prepared by using the high-grade clay or minerals, the obtained samples showed the advantages such as lower costs for raw materials, higher bending strength, higher thermal conductivity (1.63–2 times higher), low CTE, and high thermal storage density. This study demonstrated that the low-grade Ti/Fe-rich clay has excellent cost-effective potential for the preparation of thermal storage ceramics. [ABSTRACT FROM AUTHOR]

Magnesium hydroxide, Mg(OH)2, is recognized as a promising material for medium-temperature heat storage, but its low thermal conductivity limits its full potential application. In this study, thermal enhancement of a developed magnesium hydroxide-potassium nitrate (Mg(OH)2-KNO3) material was carried out with aluminum oxide (Al2O3) nanomaterials. The theoretical results obtained through a molecular dynamics (MD) simulation approach showed an enhancement of about 12.9% in thermal conductivity with an optimal 15 wt% of Al2O3. There was also close agreement with the experimental results within an error of ≤10%, thus confirming the reliability of the theoretical approach and the potential of the developed Mg(OH)2-KNO3 as a medium heat storage material. Further investigation is, however, encouraged to establish the long-term recyclability of the material towards achieving a more efficient energy storage process. [ABSTRACT FROM AUTHOR]

Personal thermal management materials integrated with phase-change materials have significant potential to satisfy human thermal comfort needs and save energy through the efficient storage and utilization of thermal energy. However, conventional organic phase-change materials in a solid state suffer from rigidity, low thermal conductivity, and leakage, making their application challenging. In this work, polyethylene glycol (PEG) was chosen as the phase-change material to provide the energy storage density, polyethylene oxide (PEO) was chosen to provide the backbone structure of the three-dimensional polymer network and cross-linked with the PEG to provide flexibility, and carbon nanotubes (CNTs) were used to improve the mechanical and thermal conductivity of the material. The thermal conductivity of the composite fiber membranes was boosted by 77.1% when CNTs were added at 4 wt%. Water-resistant modification of the composite fiber membranes was successfully performed using glutaraldehyde-saturated steam. The resulting composite fiber membranes had a reasonable range of phase transition temperatures, and the CC4PCF-55 membranes had melting and freezing latent heats of 66.71 J/g and 64.74 J/g, respectively. The results of this study prove that the green CC4PCF-55 composite fiber membranes have excellent flexibility, with good thermal energy storage capacity and thermal conductivity and, therefore, high potential in the field of flexible wearable thermal management textiles. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) have emerged as an intriguing option for the storage of thermal energy because of their remarkable capacity to store latent heat. However, the practical application of these materials is hindered by their low thermal conductivity and limited photo-absorbance. For this investigation, graphene nanoplatelets (GNP) and multiwall carbon nanotubes (MWCNT) hybrid nanoparticles were disseminated in RT-54HC organic PCMs at different weight fractions. The nanoparticles were incorporated into the base PCMs using a melt blending technique. Based on the findings, one combination of GNP to MWCNT in a 0.25:0.75 ratio has shown the highest thermal conductivity, with an increase of 40% (0.28 Wm−1 K−1) compared to other hybrid combinations. This breakthrough could potentially open new avenues in the field of thermal energy storage. The chemical stability of the hybrid nanoparticle dispersed composites was assessed through FTIR analysis. In addition, the composites exhibited excellent thermal stability, maintaining their structural integrity even at temperatures as high as 300 ℃. The melting temperature of the composites also showed minimal variation. Based on the evaluation of latent heat enthalpy, the organic PCM known as base RT-54HC demonstrated a heat storage capacity of 230 J/g. However, the composites exhibited a slight decrease in latent heat with increasing nanoparticle weight fraction. In addition, the composite with added hybrid nanoparticles demonstrated an increase in optical absorbance, accompanied by a decrease in transmissibility. Therefore, the hybrid nano-enhanced composites have demonstrated enhanced thermo-physical properties, making them not only suitable but also highly promising for use in applications with mid-range melting temperatures. [ABSTRACT FROM AUTHOR]

Featured Application: This work on 3D-printed TPU/MWCNT/PCM composites offers information on materials with significant potential for applications in advanced thermal management systems. These materials can be employed in smart textiles, wearable electronics, or flexible sensors, where precise control over temperature regulation and thermal conductivity is essential. These composites' enhanced electrical conductivity and tunable thermal properties make them promising candidates for multifunctional devices that require efficient heat dissipation, strain sensing, or even self-regulating thermal insulation. In this work, multiwalled carbon nanotubes (MWCNTs) were melt-compounded into a novel thermal energy storage system consisting of a microencapsulated paraffin, with a melting temperature of 6 °C (M6D), dispersed within a flexible thermoplastic polyurethane (TPU) matrix. The resulting materials were then processed via Fused Filament Fabrication (FFF), and their thermo-mechanical properties were comprehensively evaluated. After an optimization of the processing parameters, good adhesion between the polymeric layers was obtained. Field-Emission Scanning Electron Microscopy (FESEM) images of the 3D-printed samples highlighted a uniform distribution of the microcapsules within the polymer matrix, without an evident MWCNT agglomeration. The thermal energy storage/release capability provided by the paraffin microcapsules, evaluated through Differential Scanning Calorimetry (DSC), was slightly lowered by the FFF process but remained at an acceptable level (i.e., >80% with respect to the neat M6D capsules). The novelty of this work lies in the successful integration of MWCNTs and PCMs into a TPU matrix, followed by 3D printing via FFF technology. This approach combines the high thermal conductivity of MWCNTs with the thermal energy storage capabilities of PCMs, creating a multifunctional nanocomposite material with unique thermal management properties. [ABSTRACT FROM AUTHOR]

Among metal‐based phase change materials (PCMs), Al and its alloys have garnered significant attention due to their high latent heat and high thermal conductivity. However, challenges such as leakage, corrosion, and oxidation have limited their widespread application. Numerous researches have demonstrated that encapsulating Al and its alloy PCMs is one effective way to address these problems. This review provides a comprehensive overview of the characteristics, encapsulation strategies, and applications of Al and its alloy PCMs. First, the advantages and thermal properties of Al and its alloy PCMs are introduced, and their problems are then discussed. Subsequently, various encapsulation strategies that are expected to solve the above problems are summarized and compared. Additionally, the applications of Al and its alloy PCMs in solar thermal energy storage, catalysis, and electric vehicles are reviewed. Finally, current challenges, potential solutions, and the key direct of future study are presented. [ABSTRACT FROM AUTHOR]

Thermal energy storage, particularly through Phase Change Materials (PCMs), is gaining significant attention for its ability to enhance storage capacity and thermal conductivity. PCMs help alleviate the strain on renewable energy sources and stabilize load fluctuations. This study integrates a novel combination of LiNO3-NaSO4·10H2O-NaCl with boron nitride into Flat Plate Collectors (FPCs) to boost system performance. This Composite Phase Change Material (CPCM) increases latent heat value by up to 245.80 kJ, enhancing thermal decomposition and absorption rates while reducing heat losses. Boron nitride improves thermal conductivity by 25%, from 1.378 W/m·K to 5.543 W/m·K, increasing the CPCM's charging rate. The specific heat capacity rises from 4.2 J/g·°C to 5 J/g·°C at a maximum temperature of 90°C. As a result, the collector's efficiency improves by 15%, achieving an overall system efficiency of 88%. Water serves as the heat transfer fluid, and simulations are conducted using Python in Anaconda Jupyter Notebook. [ABSTRACT FROM AUTHOR]

Electric vehicles have the potential to address humanity's issues of environmental deterioration and energy scarcity. Electric vehicles frequently use lithium-ion batteries as their power source. The heat is generated when the batteries are subjected to high-power charging and discharging loads. This results in a considerable loss in battery life and raises the possibility of a battery explosion. As a result, quick heat dissipation from the cells is required to ensure safe operation and longer battery life cycles. Air cooling is the most basic type of thermal management; yet, due to its poor thermal conductivity, it has its restrictions. Liquid cooling agents are superior to air cooling systems in terms of thermal control. Liquid cooling, on the other hand, added complexity to the working system, increased operating costs, and increased total system weight. A similar problem might be seen when applying the heat pipe concept of cooling systems. PCM provides several advantages over above mentioned three cooling technologies, but it also has a limited heat storage capacity and poor thermal conductivity. As a result, a hybrid BTMS paradigm emerges. However, research on hybrid techniques is still insufficient. To make effective hybrid BTMS technology, efforts are being undertaken, and earlier research on the hybrid is also summarized in this study. [ABSTRACT FROM AUTHOR]

Sorption heat transformers and thermal energy storage systems are emerging technologies that utilize and store low-grade waste heat for heating and cooling applications. The performance of sorption systems is not only affected by systems' operating conditions, and overall systems' design but also by sorption material or composite parameters such as thermal diffusivity, composition, and pore structure, among others. In this study, CaCl 2 -based salt-in-porous-matrix composites of different compositions and coating thicknesses were synthesized. During synthesis, salt to silica gel and polyvinyl alcohol to silica gel ratios were fixed and the thermal additive (expanded natural graphite) to silica gel ratio was varied with care from 0 to 0.26 (or 0 to 20.5 wt.%, additive to silica gel ratio). The thickness of samples varied from 2.3 to 8.3 ± 0.1 mm. The composites were characterized by a transient plane source (thermal conductivity and thermal diffusivity), nitrogen adsorption porosimetry (specific surface area and total pore volume), and thermogravimetric sorption analysis (water sorption equilibrium) methods. A custom-built gravimetric large pressure jump (G-LPJ) testbed was used to study water sorption kinetics (water uptake vs. time) for selected samples. The thermal conductivity and diffusivity of the studied composite samples have shown significant enhancements, e.g., 240% (0.11 W/(m·K) vs. 0.37 W/(m·K)) and 310% (0.21 mm2/s vs. 0.87 mm2/s), respectively, by adding 12.5 wt.% expanded natural graphite (additive to silica gel ratio is 0.14) as a thermally conductive additive (additive to silica gel ratio) because of thermal percolation effect. This ratio of expanded natural graphite to silica gel was found to be optimal for studied composition. The results indicate that sorption composites with higher thermal diffusivity offer notably higher specific cooling power and improved sorption kinetics, compared to the composites without expanded natural graphite of the same thickness (850 W/kg vs. 480 W/kg at 70% water conversion for samples with thickness of 5.3 mm). [ABSTRACT FROM AUTHOR]

The increasing global population has intensified the demand for energy and food, leading to significant greenhouse gas (GHG) emissions from both sectors. To mitigate these impacts and achieve Sustainable Development Goals (SDGs), passive thermal storage methods, particularly using phase change materials (PCMs), have become crucial for enhancing energy efficiency and reducing GHG emissions across various industries. This paper discusses the state of the art of bio-based phase change materials (bio-PCMs), derived from animal fats and plant oils as sustainable alternatives to traditional paraffin-based PCMs, while addressing the challenges of developing bio-PCMs with suitable phase change properties for practical applications. A comprehensive process is proposed to convert bacon fats to bio-PCMs, which offer advantages such as non-toxicity, availability, cost-effectiveness, and stability, aligning with multiple SDGs. The synthesis process involves hydrolysis to break down fat molecules obtained from the extracted lipid, followed by three additional independent processes to further tune the phase change properties of PCMs. The esterification significantly decreases the phase transition temperatures while slightly improving latent heat; the UV-crosslinking moderately raises both the phase transition temperature and latent heat; the crystallization remarkably increases the both. The future research and guidelines are discussed to develop the large scale manufacturing with cost effectiveness, to optimize synthesis process by multiscale modeling, and to improve thermal conductivity and latent heat capacities at the same time. [ABSTRACT FROM AUTHOR]

Diatomite's most common application is its use as a sorbent for petroleum substances. Since paraffin is a petroleum derivative, this paper investigates the sorption capacity of diatomite to absorb it. In this paper, the physical and chemical properties were studied for 4 different fractions of diatomite (0–0.063 mm; 0–2 mm; 0.5–3 mm; and 2–5 mm) in the crude and calcined states, and the sorption capacity of diatomite earth for absorbing paraffinic phase-change substances was determined. The physical and chemical studies of the material included conducting an oxide chemical composition analysis using XRF, examining the composition of the mineral phases using X-ray diffraction, and determining the particle size, porosity, and thermal conductivity of the diatomite. Morphology images were also taken for all 8 diatomite variants using scanning electron microscopy. Each fraction was subjected to static calcination at 850 °C for 24 h. The results showed that the calcination of the diatomite increased the porosity of the material and reduced the thermal conductivity coefficient, and most importantly, the sorption capacity to absorb paraffins. The highest sorption capacity was characterized by calcined diatomite powder, that is, diatomite with the smallest particle size. Absorption of paraffinic substances by diatomite exceeding 200 wt.% is possible. Thus, diatomite is one of the feasible candidates for an economical and lightweight building material for making PCM composites for thermal energy storage in buildings. [ABSTRACT FROM AUTHOR]

Phase change material (PCM)‐based heat storage systems utilize the absorption or release of latent heat during a phase change of the storage material to store thermal energy. Nevertheless, the effectiveness of these systems is restricted by the shape and structure of their confinement, as well as the heat conductivity of the storage material. This work investigates a novel method to enhance the effectiveness of PCM systems by concurrently utilizing two techniques: the inclusion of nanoparticles and the alteration of the system's geometry. Introducing nanoparticles enhances the thermal conductivity of the storage medium while altering the shape, which improves heat transfer efficiency by adjusting the surface area available for heat exchange. RT‐35 was tested for use in latent heat thermal energy storage systems for space heating and cooling. With a melting point of 35°C, RT‐35 was chosen to moderate building temperatures by storing and releasing thermal energy for space heating and cooling. The results indicate that using nanoparticles and adjusting shape can greatly enhance the effectiveness of PCM systems. By incorporating Al2O3 nanoparticles, the melting time of the PCM was reduced by 20% compared to the pure PCM, and it is more efficient than the best case of shape modification. These findings indicate that including nanoparticles and modifying the shape are effective methods to improve the performance of heat storage devices. This technology's potential surpasses this study's limits and can be utilized in diverse applications, including solar thermal energy storage, district heating and cooling, and industrial process heat. [ABSTRACT FROM AUTHOR]

Two nanoprecursors with capping agents were incorporated in stearyl alcohol–adipic acid combination phase change material (PCM) in this study. The addition of nanomaterials made the eutectic reliable in the manner of its thermal properties like higher enthalpy, degradation point, and more compatible with the metal encapsulation materials when compared with the pristane eutectic. The importance of nano‐metal oxides in parent material was shown by the reduced time frame of the PCM's thermal energy storing and releasing process for space heating applications. The specific heat capacity of both the aluminum and titanium oxide nanocomposites were greater than the eutectic, which indicates that the material can retain more energy. The thermal conductivities of base material and nanocomposite PCMs were 0.2686, 0.2815, and 0.4395 W/mK at 40°C, and the highest percentage increment of nanocomposites was seen as 9.19% and 63.62% at varied encircled temperatures. The crystal structure and chemical disintegration were evinced with the X‐ray diffractometer results of the composites. [ABSTRACT FROM AUTHOR]

A multifunctional microencapsulated phase change material (PW@CaCO3/Y2O3) with both photoluminescence and thermal energy storage/release properties has been prepared by in situ polymerization. The material is based on the phase change material paraffin wax (PW) as its core, and the highly thermally conductive inorganic material CaCO3 is selected as the shell material to which a nano-Y2O3 material is attached. Five samples with different amounts of nano-Y2O3 incorporated in the shell are prepared. The microscopic morphology, chemical composition, crystal structure, thermal energy storage properties, thermal conductivity, thermal stability, as well as fluorescence spectra and intensities of the samples are experimentally measured and compared. The luminescence properties of nano-Y2O3 and the light enhancement phenomenon of microencapsulated phase change materials are also analyzed. The thermal properties are investigated, and it is found that the PC-Y3 sample (i.e., the mass ratio of PW:CaCO3:nano-Y2O3 is 100:100:3.0) exhibits the best thermal performance among the five samples with a melting enthalpy of (87.5 ± 2.5) J/g, an encapsulation efficiency of (61.9 ± 1.2)%, a thermal energy storage efficiency of (62.1 ± 1.5)%, an average specific heat capacity of (1.38 ± 0.21) kJ/(kg K) in solid phase (10–20 °C) and (1.46 ± 0.02) kJ/(kg K) in liquid phase (70–80 °C), and a thermal conductivity of (1.55 ± 0.01) W/(m K) in solid phase that is six times that of the solid PW. A study of the optical properties revealed that the microcapsules emitted blue light at an excitation wavelength of 290.0 ± 2.2 nm. The fluorescence intensity appeared to be enhanced with the addition of nano-Y2O3. This microencapsulated phase change material has potential applications in areas where synchronization of fluorescence and thermal modulation is required; for example, some specific fluorescent sensors that are very sensitive to heat should operate at a fixed low temperature. [ABSTRACT FROM AUTHOR]

A multifunctional microencapsulated phase change material (PW@CaCO3/Y2O3) with both photoluminescence and thermal energy storage/release properties has been prepared by in situ polymerization. The material is based on the phase change material paraffin wax (PW) as its core, and the highly thermally conductive inorganic material CaCO3 is selected as the shell material to which a nano-Y2O3 material is attached. Five samples with different amounts of nano-Y2O3 incorporated in the shell are prepared. The microscopic morphology, chemical composition, crystal structure, thermal energy storage properties, thermal conductivity, thermal stability, as well as fluorescence spectra and intensities of the samples are experimentally measured and compared. The luminescence properties of nano-Y2O3 and the light enhancement phenomenon of microencapsulated phase change materials are also analyzed. The thermal properties are investigated, and it is found that the PC-Y3 sample (i.e., the mass ratio of PW:CaCO3:nano-Y2O3 is 100:100:3.0) exhibits the best thermal performance among the five samples with a melting enthalpy of (87.5 ± 2.5) J/g, an encapsulation efficiency of (61.9 ± 1.2)%, a thermal energy storage efficiency of (62.1 ± 1.5)%, an average specific heat capacity of (1.38 ± 0.21) kJ/(kg K) in solid phase (10–20 °C) and (1.46 ± 0.02) kJ/(kg K) in liquid phase (70–80 °C), and a thermal conductivity of (1.55 ± 0.01) W/(m K) in solid phase that is six times that of the solid PW. A study of the optical properties revealed that the microcapsules emitted blue light at an excitation wavelength of 290.0 ± 2.2 nm. The fluorescence intensity appeared to be enhanced with the addition of nano-Y2O3. This microencapsulated phase change material has potential applications in areas where synchronization of fluorescence and thermal modulation is required; for example, some specific fluorescent sensors that are very sensitive to heat should operate at a fixed low temperature. [ABSTRACT FROM AUTHOR]

Multiform NiO nanowalls with a high specific surface area were constructed in situ on carbon foam (CF) to construct NiO@CF/OD composite phase change materials (CPCMs). The synthesis mechanism, microstructures, thermal management capability, and photothermal conversion of NiO@CF/OD CPCMs were systematically studied. Additionally, the collaborative enhancement effects of CF and multiform NiO nanowalls on the thermal properties of OD PCMs were also investigated. NiO@CF not only maintains the porous 3D network structure of CF, but also effectively prevents the aggregation of NiO nanosheets. The chemical structures of NiO@CF/OD CPCMs were analyzed using XRD and FTIR spectroscopy. When combined with CF and NiO nanosheets, OD has high compatibility with NiO@CF. The thermal conductivity of NiO@CF/OD-L CPCMs was 1.12 W/m·K, which is 366.7% higher than that of OD. The improvement in thermal conductivity of CPCMs was theoretically analyzed according to the Debye model. NiO@CF/OD-L CPCMs have a photothermal conversion efficiency up to 77.6%. This article provided a theoretical basis for the optimal design and performance prediction of thermal storage materials and systems. [ABSTRACT FROM AUTHOR]