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In this study, composite phase change materials (CPCMs) comprising hexadecylamine (HDA) (C 16 H 35 N), disodium hydrogen phosphate dodecahydrate (DHPD) (Na 2 HPO 4 ·12H 2 O), and expanded graphite (EG) were prepared using the demulsification method. These CPCMs exhibit high latent heat and stable thermal properties. This approach effectively mitigates the issues of substantial supercooling and poor thermal conductivity commonly associated with DHPD and HDA. Additionally, the inclusion of EG imparts superior morphological stability to the CPCMs. The HDA/DHPD/EG CPCMs demonstrated robust thermal and morphological stability at temperatures below 100 °C. Their latent heat reached up to 221 J/g and remained stable at this value even after 50 cold-heat cycles, thereby indicating excellent cycling stability. When EG was incorporated at 2 wt%, the thermal conductivity of the HDA/DHPD/EG CPCMs increased to 0.751 W/(m·K), indicating that the three-dimensional network structure of EG facilitates heat conduction and offers exceptional photothermal conversion capabilities, with a photothermal conversion efficiency of up to 97.1 %. The aforementioned results highlight the promising potential of the prepared CPCMs for applications in low-temperature waste heat recovery. [ABSTRACT FROM AUTHOR]

[Display omitted] • CNTs-related composite PCMs are categorized in a new way: CNTs are usd as nanoadditives, porous supporters, and secondary network. • The research progress in the mechanism of heat transfer and phase transition of CNTs-related composite PCMs is introduced in detail. • In-depth insights into the micro-mechanism of heterogeneous interactions induced by CNTs are revealed. • The current challenges of designing CNTs-related composite PCMs are summarized. With the merits of inherent physicochemical properties of hollow structure, high mechanical strength, thermal stability, ultrahigh light absorption capacity, and ultrahigh thermal conductivity, carbon nanotubes (CNTs) are extensively used to enhance the thermal storage capabilities of solid–liquid phase change materials (PCMs). Interestingly, CNTs can act as thermally conductive additives and supporting skeletons when marring with PCMs. The state-of-the-art reviews on PCMs pay attention to carbon-based porous composite PCMs or nanoparticle dispersed PCMs, CNTs-derived PCMs only share a small part, lacking of a comprehensive review for multifunctional CNTs compounded PCMs. Herein, focusing on the enhancement effects of CNTs on PCMs, we retrospectively describe composite PCMs with a novel category way, by using CNTs as nanoadditives, porous supporters, and secondary network. We emphasize the micro-mechanism of heterogeneous interactions induced by CNTs: crystallization behavior, interfacial thermal resistance, thermal conductivity, phonon transport. Simultaneously, we provide in-depth insight into relationship between micro structural and thermal properties of CNT-derived PCMs. As a result, some different pathways of modern utilization based on the improved PCMs are presented. Finally, we outline the current challenges of designing CNTs to enable advanced functional thermal storage materials. The review aims to inspire clever use of CNTs into PCMs for targeted applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Upcycling materials were produced composite using clothing waste and PCMs. • Clothing waste, without sorting, was utilized in specimens via a physical process. • The composites demonstrated enhanced latent heat storage capacity. • Clothing waste is valuable for building due to its high insulation. The current volume of clothing waste reached 115 million tons in 2021 and is projected to increase to approximately 150 million tons by 2030. This significant surge in clothing waste has prompted heightened discussions regarding environmentally friendly recycling methods. Clothing presents complex properties, posing substantial challenges to recycling and usually resulting in environmental pollution when disposed. In this study, our recycling approach capitalizes on the differing melting points of textiles. This transformation was achieved through a physical process that included an opening procedure and high temperature heat compression. Textile materials exhibit exceptional thermal properties. Through experimentation on 50 g fiber specimens, thermal conductivities similar to commercial insulation materials were observed, registering an average of 0.0592 W/m·K at 20 °C and 0.06053 W/m·K at 40 °C. This study explores the impregnation of phase change materials (PCMs) into clothing waste-based specimens, equipping them with heat storage capabilities. During the experimental phase, we employed three distinct types of PCMs to evaluate their thermal properties and heat storage capacities in relation to their respective melting temperatures. Through thermal properties analysis, we determined the latent heat capacity of each specimen, ranging from a minimum of 6.63 J/g to a maximum of 75.81 J/g. Our observations indicated a reduction in peak temperature and time-leg effects attributable to the use of PCMs for surface heat flow. This research underscores the superior thermal performance of construction and building materials derived from clothing waste, enhanced by the integration of PCMs, when compared to traditional materials and other waste-derived alternatives. [ABSTRACT FROM AUTHOR]

Phase change materials (PCM) have attracted much attention in the field of thermal energy storage because of exceptional heat storage capacity, stable operating temperature, and recyclability. However, organic phase change materials, represented by palmitic acid (PA), are limited by inherent leakage problem, unsatisfactory thermal responsiveness and inefficient photo-thermal storage capacity, which severely hamper the development of PCMs technology. As a means of addressing these challenges, we developed one novel support material with 2D/0D structure for palmitic acid via thermal polymerization, specifically, in which highly dispersed Ag quantum dots (Ag QDs) was firmly anchored on graphitic carbon nitride (g-C 3 N 4). PA was further infiltrated into the layered structure of nanoporous g-C 3 N 4 /Ag QDs to successfully synthesize novel shape-stabilized PA/g-C 3 N 4 /Ag QDs composite phase change materials (CPCM). On the one hand, benefiting from the tightly stacked porous structure of g-C 3 N 4 /Ag QDs, PA is effectively encapsulated to avoid leakage problem during the solid-liquid transition with a superior adsorption capacity up to 65 %. On the other hand, the combination of g-C 3 N 4 and Ag QDs in PA/g-C 3 N 4 /Ag QDs CPCM demonstrated a synergistic effect resulting in faster heat transfer capability and more efficient solar energy capture capability compared to pure PA, which is capable of dual utilization of heat and solar energy. The newly developed PA/g-C 3 N 4 /Ag QDs CPCM features a high melting latent heat and an appropriate phase change temperature, which are 128.35 J/g and 61.92 °C, respectively. The corresponding solidification enthalpy and temperature are 121.70 J/g and 60.02 °C. The photo-thermal conversion efficiency of the material is improved to 78.6 %, facilitating a rapid capture and storage of solar energy. Furthermore, through the optimization of the preparation process, Ag QDs are densely anchored on the surface of g-C 3 N 4 , which retains the excellent properties of metallic silver while eliminates the metal agglomeration phenomenon after repeated utilization of CPCMs. PA/g-C 3 N 4 /Ag QDs CPCM is proved to be extremely recyclable and thermally stable after massive thermal cycles. This innovative and operational encapsulation modified method significantly optimizes the practicality of phase change materials. The obtained shape-stabilized PA/g-C 3 N 4 /Ag QDs CPCM is more versatile, and its unique comprehensive properties can provide high-quality materials for photo-thermal storage systems. • 2D/0D structure g-C 3 N 4 /Ag QDs are constructed to encapsulate PA. • Novel PA/g-C 3 N 4/ Ag QDs CPCM is developed with outstanding and stable thermochemical properties. • PA/g-C 3 N 4 /Ag QDs CPCM exhibits stronger photo-capture capability with increased photo-thermal conversion efficiency of 78.6 %. • By the optimized synthesis process, CPCM has outstanding shape and structural stability to overcome metal agglomeration. [ABSTRACT FROM AUTHOR]

Systematization and analysis of standalone waste materials that can serve as phase change materials (PCMs), and composites consisting of commercially available PCMs combined with organic and inorganic waste materials is presented. Within the conducted review research, obtained thermal properties of so far investigated waste-derived PCMs were presented, assessing, among other, their latent heat storage capacity, thermal conductivity, and thermal and cyclic stability. Refined coconut oil and Allanblackia oil exhibited exceptional thermal and cyclic stability along with high values of latent heat, amounting 105 kJ kg−1 and 81 kJ kg−1, respectively. In some cases incorporation of waste materials significantly improved thermal properties, e.g. the addition of carbonized waste tire rubber to dodecyl alcohol increased its thermal conductivity to 0.431 W m−1K−1, representing an increase by a factor of 2.3. This enhancement led to a 17.2 % reduction in heating times and a 20 % reduction in cooling times compared to using pure PCM. Besides providing extensive data on thermophysical properties of phase change composites, the study provides a comprehensive overview of their applications, economic feasibility, and environmental implications. This extensive review shows the potential of waste-derived PCMs to contribute to a circular economy by repurposing waste materials for sustainable energy solutions and reducing environmental impacts. The findings indicate that while valorising wastes or by-products as latent thermal energy storage materials is feasible, more research efforts are required towards potential commercialization. • Valorisation of waste materials for LTES (Latent Thermal Energy Storage) applications. • Categorized and analysed applications of waste in LTES systems. • Summarized thermal properties of waste-based phase change materials (PCMs). • Economic and environmental aspects of waste-based PCM discussed. • Future directions for usage of waste-based PCMs in LTES elaborated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Facile synthesis of eco-friendly wheat husk biomass derived microparticle. • Maximum thermal conductivity increments of the A-70 + WH composite is 66.66 %. • Heating enthalpy increment of WH derived PCM composite is 4.57 %. • Proven thermal reliability of A-70 + WH composite for 500 thermal cycles. Organic phase change materials (PCM) exhibit poor volumetric latent heat storage capacity and have low thermal conductivity. Therefore, this study aims to develop a PCM composite with better thermal conductivity and latent heat by dispersing newly synthesized wheat husk microparticles in Paraffin wax (A-70) PCM via a two-step technique. As per the results, the developed composite materials latent heat and thermal conductivity were 217.1 J/g & 0.45 W/m K, which was 4.57 % and 66.66 % higher than base PCM, respectively. Moreover, after 500 thermal cycles, the newly synthesized composite was found to be thermally and chemically stable. [ABSTRACT FROM AUTHOR]

• Influence of natural convection on the experimental characterization of liquid thermal conductivity of octadecane. • Inverse method based on heat flux measurements to characterize the thermal conductivity and specific heat capacity of the PCM at liquid state. • A comparison of the Nusselt numbers estimated from combining the numerical and experimental results with the known correlations for the different experimental conditions was carried out. This paper numerically makes use of the inverse method coupled with experimenal results obtained through the fluxmetric method in the Laboratoire de Génie Civil et géo-Environnement (LGCgE) to determine the specific heat, thermal conductivity and thermal expansion coefficient of liquid n -octadecane in an enclosure accounting for natural convection present in the experimental system. The impact of ommiting the presence of natural convection for the thermophysical propertie determination is studied and shows very little effect on the specific heat value but a large error (by a factor of two in this study) on the thermal conductivity value. The correct properties identified when accounting for natural convection (ρ = 2150 J/kg‧K; k = 0.16 W/m‧K; β = 9.38 × 10−4 K−1) are consistent with the literature. Additional direct numerical work was done to determine the impact of using the different thermal conductivity values, comparing numerical to additional expermental restuls where natural convection was stronger. The thermal conductivity value played a minial role when simulating the behavior of the systems rightly accounting for natural convection. Combining the numerical and experimental resutls allowed the calculation of encolsure specific Nusselt numbers for the various experimental conditions used and a comparison to known correlations. It was determine that the Nusselt number obtained in the liquid n -octadecane were larger by 10 to 48%. [ABSTRACT FROM AUTHOR]

This research aims to evaluate drying kinetics and thermal performance, influenced by the type of glazing. A novel solar dryer that has a phase-change-materials (PCM), heat-recovery (HR), V-groove absorber, and photovoltaic (PV). The research was carried out on jelly candy objects treated with the influence of glazing (single-double-vacuum glazing). Jelly candy has an equilibrium moisture content using single, double, and vacuum glazing collectors, namely 11.59 % (wb), 9.94 % (wb), and 8.83 % (wb), respectively. Then, all types of glazing have an average drying rate value of 0.05 % (wb)/min for three working days. Based on the model accuracy test indicate that the Page and Verma et al. model are the best models for predicting drying kinetics in jelly candy. Specific heat (Cp) and thermal conductivity (k) decreased as the equilibrium moisture content decreased with a range of >1000–2250 J/kg°C and >0.05–0.11 W/m.K, respectively. The heat-utilization-factor (HUF) and coefficient-of-energy (COE) values show an average value of 0.79 and 0.21. Various glazing shows an average heat-gain-percentage (HGP) of 24.82 %. Drying efficiency of indirect solar dryers with single, double, and vacuum solar collectors, namely 83.6 %, 85.2 %, and 85.2 %, respectively. SEM-EDS analysis shows that the surface of the jelly candy is filled with sugar crystals and contains several elements (C,O,K,Fe). [Display omitted] [ABSTRACT FROM AUTHOR]

Chloride molten salt is a promising thermal storage material owing to its high thermal storage density, but the low thermal properties need to improved. Accordingly, a new LiCl/SiC with a SiC mass fraction of 1.0 wt% based-molten salt phase change material (PCM) was proposed to recycle the LiCl contained in the lithium-ion batteries, and the calculation and improvement method of thermal properties including thermal conductivity, specific heat capacity, melting enthalpy and viscosity etc., were developed and investigated using molecular dynamics (MD) simulations. The microstructure characteristics of LiCl/SiC molten salt were also investigated. The microscopic transformation of the structure was observed, and the results show that the self-diffusion coefficient of the system can be decreased by 4.57% with the addition of SiC nanoparticles. The thermal conductivity of the system can be increased by an average of 2.43%, and the shear viscosity can be increased by 5.4%. Besides, the melting enthalpy was decreased by 8.85%, but the specific heat capacity only strengthened by 0.8% average in the studied temperature range. It is expected be helpful for the thermal performance enhancement of recycled molten salt. • Recycling lithium chloride from waste lithium-ion batteries as PCM for thermal energy storage was proposed • Microstructure of LiCl/SiC based composite PCM with 1.0 wt% fraction of nano SiC particle was established. • MD simulations were conducted to investigated the thermal performance. [ABSTRACT FROM AUTHOR]

Flexible phase change materials (FPCM) with PA/SEBS/POE were prepared by melt blending method. The microstructure, thermal properties and cycle stability were characterized. The results show that a suitable SEBS and POE ratio can not only provide flexibility, prevent the leakage of paraffin, but also enhance the thermal conductivity. Then expanded graphite (EG) was added to prepare FPCM-EG and to further improve the performance. The experimental results show that the thermal conductivity and cycle stability increase with EG content increasing. When EG content is 15 %, the thermal conductivity is 3.572 W·m−1·K−1, which is 15.5 times of paraffin. And the leakage rate is less than 0.03 % after 20 cycles. After that, the FPCM-EG is used for thermal management of photovoltaic cell-thermoelectric (PV-TE) coupling system under simulated electric heating. The effects of EG content, heating flux and heat dissipation condition on temperature control and thermoelectric conversion performance were explored. The experimental results show that the FPCM-EG can significantly reduce heating surface temperature, improve power output and relieve the impact of heating flux variation. When EG content increases from 10 % to 15 %, the maximum heating surface temperature is reduced from 40.1 °C to 37.8 °C, and the power output is improved by 33.3 %. • Flexible PCMs with high thermal conductivity and latent heat were prepared. • The thermal conductivity is 3.572 W m−1·K−1, latent heat is 134.84 kJ/kg. • After 20 cycles, the leakage rate is less than 0.03 %. • The prepared FPCMs was used for thermal management of PV-TE system. • The surface temperature is reduced and power output is improved significantly. [ABSTRACT FROM AUTHOR]

[Display omitted] • The EG-PAAS network enhances cPCMs' mechanical strength and thermal performance. • Introducing PAAS polymer network into EG skeleton. • Summarized the optimal process conditions for preparing cPCMs. • cPCMs can be used for efficient cold chain logistics transportation. The growing demand for high-quality food and medicine has propelled the expansion of the global cold chain logistics market. Passive cold chain logistics, utilizing phase change materials (PCMs), has emerged as an advanced and environmentally friendly technology. This study addresses current challenges in phase change materials, including leakage and low mechanical strength, by introducing a novel composite phase change material (cPCM) with enhanced thermal conductivity and flexibility. The expanded graphite-sodium polyacrylate (EG-PAAS) dual network framework, formed through vacuum impregnation and in-situ polymerization, results in a cPCM (H 2 O@EG-PAAS) with high thermal conductivity (5.64 W·m−1·K−1) and substantial latent heat (263.1 J·g−1). Addressed prolonged cooling times in phase change materials, accomplishing rapid cooling and uniform temperature distribution. The 8 L insulation box was maintained below 8 °C for 1124.1 min, rendering it a promising solution for efficient and flexible cold chain transportation. [ABSTRACT FROM AUTHOR]

Molten salt phase change materials (MSPCMs) provide strong support for the long-term and stable operation of new energy systems. This study focuses on LiNO 3 (high latent heat, low melting temperature), NaNO 3 (an important component in solar salts), and binary eutectic nitrate (LiNaNO 3). The aim is to explore eutectic nitrate that matches lower working temperature requirements by eutectic reaction. The other aim is to enhance the specific heat and thermal conductivity of nitrates by adding nanoparticles (NPs) with different microstructures. The NPs include multi-walled carbon nanotubes (MWCNT), graphene nanoplatelets (GNP), AlN, BN, and SiC. The distribution patterns of nitrate molecules near NPs were investigated under the influence of interaction strength through molecular dynamics. The enhancement of thermal transport is decided by phonon vibrations, interface thermal resistance, and heat pathway. NPs can significantly weaken the melting enthalpy and limit the enhancement of thermal conductivity by disrupting the eutectic microstructure of LiNaNO 3 , which is different from the mechanism of NPs' action on unitary nitrates. MWCNTs exhibit the most significant enhancement in thermal conductivity and specific heat of nitrates, which is due to the diffusion of nitrate molecules in the MWCNT. The in-plane phonon vibrations of GNP contribute slightly to the thermal transport in the vertical plane direction, resulting in limited enhancement of thermal transport. Therefore, we propose principles for selecting NPs doped into eutectic salts, which should ensure that the interaction strength between NPs and both unitary nitrates is similar or that their microscopic structure can maintain the integrity of the eutectic structure. [Display omitted] • The thermal conductivity and specific heat of nitrates were experimentally enhanced with maximum rate of 237.72 %, 95.67 %. • NPs weaken the melting enthalpy of LiNO 3 and NaNO 3 by binding them on the surfaces of NPs. • For LiNaNO 3 , the disruption of eutectic structure by NP will weaken enthalpy and limit enhancement on thermal conductivity. • The diffusion of nitrate molecules inside the structure of MWCNT leads to diverse impact on thermal properties of nitrates. • A principle for selecting NPs doped into eutectic salts is proposed to more effectively enhance heat storage efficiency. [ABSTRACT FROM AUTHOR]

Integration of phase change materials (PCMs) into buildings contributes to mitigating indoor temperature fluctuations, offering opportunities for alleviating energy crisis. However, prevalent PCM integration methods commonly suffer from shortcomings in mechanical properties, compatibility, and environmental sustainability, restricting their applications. This study developed a novel shape-stabilized PCM (SSPCM) using cenospheres from coal-fired power waste and bio-based PCMs from vegetable oil by-products, subsequently sealed with silica coatings to inhibit PCM leakage and improve thermal stability, termed as SCS@PCM, exhibiting melting enthalpy up to 103.9 J/g. SCS@PCM was then integrated into cement mortars by replacing fine sand to fabricate thermal storage cement-based materials (TSCM), followed by assessments of their microstructural, mechanical, and thermal properties. The results showed that the silica coating helps to lowrer adverse impact of SCS@PCM on the compressive strength and thermal conductivity of TSCM. TSCM containing 30.0 vol% SCS@PCM reached a 28-day compressive strength of 45.3 MPa, exhibiting only a 17.4 % reduction compared to the control group, notably less than reductions observed for other SSPCMs reported in literature. Moreover, integration of SCS@PCM improved thermal storage capacities and decreased thermal fluctuation rates of TSCM, evidenced by a 4.7 ℃ decrease in peak temperature at dosage of 30.0 vol%. This study endeavors to develop an eco-friendly TSCM with excellent thermal and mechanical properties, providing insights for applications in improving the thermal regulation and energy efficiency in building roofs. • An eco-friendly, compatible, and robust shape-stabilized PCM was developed using cenospheres and bio-based PCMs. • Effective inhibition of PCM leakage and improved thermal stability of SCS@PCM was achieved by the SiO 2 coating. • SCS@PCM replaced up to 30 % by volume of fine sand without noticeable reduction in the mechanical strength of cement mortar. • SCS@PCM significantly improved the heat storage and temperature regulation capabilities of cement mortar. [ABSTRACT FROM AUTHOR]

This study explores the use of copper foam (CF) as a thermally conductive scaffold for phase change materials (PCMs), enhancing shape stability. Employing the ice template method (ITM), we fabricate a CF with a low-density, honeycomb structure and anisotropy from flake copper powders. The resulting phase change composites (PCCs), infused with paraffin wax (PW), showcase high thermal conductivity and shape retention compared to pure PW, with anisotropic heat flow due to directional channels in the CF. With a 34.4 wt% filling ratio, the PCCs achieve axial and lateral thermal conductivities of 2.85 W m−1 K−1 and 1.51 W m−1 K−1, respectively, and a thermal storage enthalpy of 158.18 J g−1. This work presents a novel method for advanced thermal energy storage and management, indicating the promise of ITM-derived CF in high-performance PCCs for diverse applications. • 3D porous copper with lighter weight, honeycomb-like and directional structure was prepared. • The composite has good form-stability and anti-leakage property. • The composite indicates high thermal conductivity of 2.85 W m−1k−1. • The composite indicates heat storage capability of 158.18 J g−1. • The composite has good anisotropic thermal conductivity. [ABSTRACT FROM AUTHOR]

The temperature range within which phase change materials (PCM) in water emulsions can effectively function is limited to 0–100 °C. In contrast, non-aqueous emulsions offer a broader temperature range for heat storage and transfers, along with greater chemical stability. This research involved the preparation of a PCM in silicone oil phase change emulsion using the emulsion inversion point (EIP) method as an alternative to high-energy methods which known for their high energy consumption and low efficiency. The emulsion was produced by gradually adding silicone oil to a mixture of lauric acid and surfactant under low-speed stirring. The study focused on assessing dispersion stability and thermal properties of emulsions with varying PCM concentrations. Results showed that similar droplet sizes can be achieved compared to high-energy methods, with average droplet sizes ranging from 5.21 to 6.89 μm for emulsions containing 5%–20% lauric acid. The phase change enthalpy of the emulsions aligned with theoretical values, showing a supercooling below 3.0 °C when PCM concentration was between 10 and 20%. Additionally, the viscosity of the emulsions decreased as the PCM concentration increased. Moreover, the addition of nanoparticles increased thermal conductivity by 19.8%, with energy storage efficiency remaining at 97.3% after thermal cycling. The emulsions also demonstrated reduced pumping power requirements by 87.3% and 99.4% at 25 °C and 50 °C, respectively, compared to the base fluid, making them promising candidates for enhancing the utilization of renewable energy sources including solar energy. • Fatty acid in oil emulsions exhibited great storage stability for 5 months. • Viscosity of the emulsions decreased as mass fraction of PCM increased. • Inclusion of nanoparticles enhanced thermal conductivity of emulsion by 19.8%. • Energy storage efficiency remained 97.3% after 100 thermal cycles. • Pumping power reduced by 99.4% for the 20% emulsion compared to base fluid. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are a crucial focus of research in the field of photothermal energy storage. However, due to their inherently low photothermal conversion efficiency, traditional PCMs absorb solar energy scarcely. The photothermal conversion ability of PCMs are usually enhanced by incorporating photothermal conversion nanoparticles. Polydopamine (PDA) is widely used in various fields due to its excellent photothermal conversion and adhesion performance. We dispersed PDA into PEG containing CuNPs to test the effect of PDA on thermal properties of cPCMs. Our team has conducted experiments to test the thermal characteristics and photothermal conversion ability of cPCMs. Results demonstrated that the addition of PDA mitigated the enthalpy loss caused by integrating CuNPs. The enthalpy of melting of cPCMs with addition of polydopamine is greater than that without polydopamine for the composites with different mass fractions. The addition of PDA in cPCMs enhanced their photothermal conversion capacity, resulting in higher temperatures being achieved within the same exposure time compared to samples without PDA. Therefore, the cPCMs with dispersed polydopamine can store higher energy. Meanwhile, PDA also improved the overall thermal conductivity of the material. Our work provided a new method to utilize the photothermal properties of polydopamine. Meanwhile, it can reduce the cost of photothermal energy storage PCMs and further improve the potential of PCM energy storage. • The PDA was dispersed into the PEG rather than on the surface. • The addition of PDA enhanced the photothermal conversion capacity of nano-copper in PEG. • The incorporation of PDA can mitigate the enthalpy reduction induced by nano-copper. • The dispersion of PDA can further improve the thermal conductivity of PEG containing copper nanoparticles. [ABSTRACT FROM AUTHOR]

• Microencapsulation of PCM with SiO 2 by Sol-gel process. • PCM@SiO2 incorporation effectively reduced concrete pavement surface temperatures, crucial for urban heat management. • Up to 30% PCM@SiO2 replacement maintained concrete strength within Indian standards, suitable for construction use. • Enhanced thermal energy storage capabilities were observed with increased PCM@SiO2 content. This study investigates the potential of enhancing thermal performance in pavement concrete by integrating microencapsulated phase change materials (PCM@SiO 2) using a Sol-gel process for encapsulation. With a concentration range from 0% to 20% in 5% increments, the effects of PCM@SiO 2 on both the mechanical strength and thermal performance of concrete were evaluated. Although the addition of PCM@SiO 2 resulted in a compromise in mechanical strength, significant improvements in thermal performance were observed, demonstrating a promising approach to mitigating temperature stresses and the urban heat island effect in pavement construction. This balance between mechanical and thermal properties underscores the potential of PCM incorporation as a strategic material choice for innovative urban development. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new type of FSCPCMs with a wide phase change temperature range were designed. • The latent heat of the prepared FSCPCMs could reach 142.5 J/g. • The FSCPCMs exhibit good thermal conductivity and thermal stability. Phase change materials (PCMs) with wide phase change temperature range, high latent heat, good thermal conductivity, and shape stability are essential for applications such as solar energy conservation and thermal management of electronic devices. Form-stable composite PCMs (FSCPCMs) with a broad phase change temperature range of 18–65 °C were successfully developed by using a mixture of eicosane and paraffin mixture along with cross-linking polyurethane as PCM, expanded graphite as thermally conductive filler and supporting material. The prepared FSCPCMs demonstrated excellent thermal stability and thermal conductivity with a latent heat up to 142.5 J/g. In conclusion, the synthesized FSCPCMs exhibit promising potential for practical applications in thermal energy storage. [ABSTRACT FROM AUTHOR]

• EG@Ag was prepared using a novel and simple electroless silver plating process. • The effect of EG@Ag on the thermal properties of erythritol has been discovered. • Substantial reduction in the supercooling of erythritol. In this paper, the composite PCMs of Erythritol (ET)/Expanded Graphite (EG)@Ag were prepared by vacuum impregnation method with EG@Ag as matrix and the ET as the phase change material (PCM). The chemical compatibility, thermodynamic properties and thermal stability of composite phase change materials (CPCMs) were systematically examined. The results illustrated that the CPCMs possessed good chemical compatibility with only physical interaction between ET and EG@Ag. The supercooling of ET/EG@Ag-8 wt% reduced by 42.13 °C, which also remain high melting and solidification enthalpy of −258.09 J/g and 187.63 J/g, respectively. The thermal conductivity of ET/EG@Ag-8 wt% reached to 2.87 W/(m·K), which resulted in an enhancement of 463 % in the thermal conductivity of ET. Thermal stability results show that all CPCMs of ET/EG@Ag present good thermal stability below 200 °C. This offers new prospects for the use of ET in the field of medium temperature phase transitions. [ABSTRACT FROM AUTHOR]

The issue of leakage in phase change materials (PCMs) severely restricts their use as thermal storage materials. In this study, waste coffee grounds-based biochar (WCG) was developed by carbonization and chemical modification as a support material for composite PCMs. The WCG/Paraffin wax (PW) composite PCMs were prepared using the melt impregnation method. The pore structure of alkali-modified biochar (OH-WCG) underwent significant development, and the surface area and total pore volume increased to 21.9 and 12 times that of unmodified biochar, respectively. Leak-free composite PCMs (OH-WCG-40) can be obtained when using OH-WCG as the support material at a biochar addition of 40 wt%. The characterization results indicated the physicochemical compatibility of the biochar in the composite PCMs with the PCMs. Differential scanning calorimetry (DSC) showed the phase transition temperature and the melting enthalpy of OH-WCG-40 were 46.28 °C and 97.69 J/g, respectively. The thermal conductivity of OH-WCG-40 was enhanced by 43% compared to pure PW. After 300 cycles, the composite PCMs exhibited nearly no change in mass and demonstrated good cycling stability. Therefore, alkali-modified biochar is a good support material for composite PCMs which can be used as a good thermoregulation material for temperature regulation of buildings and recycling of solar energy. [Display omitted] • The surface area of the NaOH-biochar is 21.9 times that of the untreated biochar. • The thermal conductivity of the composite PCM is 43% higher than that of paraffin. • The composite PCMs show no mass change after 300 cycles and had good stability. • Only 40 wt% of modified biochar is required to ensure no leakage of the paraffin. [ABSTRACT FROM AUTHOR]

Massive concrete structures are susceptible to thermal cracking due to the large surface-to-internal temperature gradients induced by the exothermic cement hydration, threatening their durability and safety. This study explored a novel thermal-tailored strategy to mitigate thermal cracking of cement-based materials by incorporating carbon fibers (CF) and liquid-metal-based microencapsulated phase change materials (MEPCM). Specifically, spherical MEPCM composed of In-Bi-Sn alloy cores coated by polyvinyl alcohol shells was prepared through a high-speed liquid-phase dispersion method, with average diameters of 36.26 μm and a high volumetric latent heat of 214 MJ/m3. The synergistic effect of CF and MEPCM on the microstructure, mechanical and thermal properties of cement mortars was further investigated. Upon adding 0.3 wt% of CF and 3.2 vol.% of MEPCM, the flexural strength of cement mortars exhibited a significant increase of 30.3 %. Microanalysis revealed that the molten MEPCM could flow to fill the pores and microcracks within its surrounding matrix and form a network skeleton with well-dispersed CF, imparting flexibility to the typically rigid cement hydrates. By this way, the thermal conductivity of cement mortars was increased by 21.7 % and internal temperature rise was decreased by 12 ℃ by adding 4.8 vol.% of MEPCM, contributing to the mitigation of risks associated with thermal cracking. The research outcomes will provide valuable insights into the development of thermal cracking-resistant cement-based materials in a highly efficient way. • Fabrication of microencapsulated phase change materials (MEPCM) based on In-Bi-Sn alloy was achieved. • The synergistic effects of carbon fiber (CF) and MEPCM on the performance of cement mortars was evaluated. • Incorporation of CF and MEPCM significantly enhanced the flexural strength and thermal conductivity of cement mortars. • Cement mortars containing 0.3 wt% CF and 4.8 vol.% of MEPCM exhibited a maximum internal temperature reduction of 12 ℃. [ABSTRACT FROM AUTHOR]

Shape-stabilized phase change material (SSPCM) are widely used as energy storage materials due to its advantages of easy preparation and adjustable scale. But the thermal conductivity enhancement of SSPCM still need to be further studied to improve the energy storage efficiency. In this work, silicone rubber (SR)/paraffin@SiO 2 (Pn@SiO 2)/graphene nanoplates (GNPs) shape-stabilized phase change materials (SPG) with different GNPs content were prepared. Pn@SiO 2 and GNPs can be homogeneously dispersed in the SR matrix due to the enhanced interfacial compatibility between Pn@SiO 2 and SR. The leakage rate of SPG composites was as low as 0.25% due to the protection of SiO 2 shell, SR matrix and GNPs. The SPG composites had excellent thermal storage properties, with the enthalpy about 50 J·g−1. The thermal conductivity of SPG composites was improved with the content of GNPs, the thermal conductivity of SPG reach 0.989 W·m−1·K−1 at a GNPs content of 10 phr. The low hardness of SPG composites above the phase change temperature can provide a more cohesive surface when applied to heat dissipation. The heat dissipation of the SPG composites in electric devices was simulated and demonstrated that the addition of GNPs made the heat dissipation rate of the SPG composites increased significantly. Therefore, the SPG composites can be applied in thermal energy storage and heat dissipation of electronic devices. [Display omitted] • The thermal conductivity enhancement of SSPCM was further discussed. • The interfacial compatibility of components in the SSPCM was enhanced by the rational strategy. • The leakage-prevention performance of SSPCM was improved with the multiple protection. • The thermal conductivity of SSPCM reach 0.989 W·m−1·K−1 due to the well-dispersed GNPs and Pn@SiO 2 in SR. • Numerical simulation was used to predict the thermal performance of SPG composites. [ABSTRACT FROM AUTHOR]

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

• A new type of polyurethane/lauric acid-stearic acid PCMs has been synthesized. • The synthesized FSPCMs possess a wide phase transition temperature range. • The PU encapsulating material exhibits both support and phase change features. • The FSPCMs maintain shape stability during phase transition without leakage. The current study employed a solvent-free method to prepare a series of crosslinked polyurethane/lauric acid-stearic acid composite form-stable phase change materials (FSPCMs). FTIR, SEM, and XRD results collectively indicate that lauric acid (LA) and stearic acid (SA) have been successfully adsorbed into the polyurethane (PU) mesh-like structure, maintaining their respective crystalline characteristics and exhibiting good compatibility. DSC and TGA data show the wide phase transition temperature range of FSPCMs from 39.6 °C to 70.0 °C, with decomposition commencing at 190.4 °C and the latent heat of FSPCM reaching 181.9 J/g. In conclusion, the broad phase transition temperature range and high latent heat of FSPCMs make them particularly suitable for thermal energy storage. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) nanosheets, such as graphene and hexagonal boron nitride, are considered as the most promising fillers for enhancing thermal conductivity of polymers and phase-change materials. Nevertheless, the effect of various 2D nanosheets on the effective thermal conductivity of composites is not fully understood, and the corresponding prediction model is still lacking, since numerous influence factors and complex thermal transfer networks are involved. This paper aims to study the macroscopically effective thermal conductivity of the nanosheets-reinforced composites in a systematical way, and develop a robust machine learning based prediction model. To this end, a series of representative volume elements are reconstructed based on the SEM observations of experimental samples, and high-throughput simulations are performed via the updated lattice Boltzmann scheme proposed in our recent work. The effects of shape, size, orientation, intrinsic thermal conductivity, interface thermal resistance, surface coating, and hybrid filling of the 2D nanosheets are clarified. This work could provide a deep insight into the effective thermal conductivity of the nanosheets-reinforced composites, and may offer important guidelines for the custom-design of polymer and phase-change composites with targeted thermal performances. [Display omitted] [ABSTRACT FROM AUTHOR]

Concerns over the escalating energy crisis have prompted extensive study and application of energy storage technology as a means to augment energy efficiency. Molten salts (MSs) feature prominently as phase change material (PCM) due to their considerable latent heat, broad operating temperature range, high heat storage density, and cost-effectiveness. This paper presents a survey of the advancements in the study of preparation methods, heat transport characteristics, phase change characteristics, and thermal stability of MSs over the past three years. Heat transport characteristics encompass thermal conductivity, specific heat capacity, thermal diffusivity, and viscosity. Phase change characteristics include melting point, latent heat, subcooling, nucleation methodology, and heat storage density. The review also explores the promising domain of nano-enhancement technologies and the analysis of MSs' thermal conductivity via phonons. [Display omitted] • Recent progress in properties modifications of molten salts is reviewed. • Adding skeleton materials affects the thermal storage performance. • Nanoparticles are the properties enhancer of molten salts. • Preparation techniques of molten salts impacts the thermal storage performance. • Waste treatment is applied in thermal energy storage of MSs. [ABSTRACT FROM AUTHOR]

The thermal conductivity, thermal cycling behaviour, and deformation resistance of composite phase change materials (cPCMs) based on sodium acetate trihydrate (SAT) can be effectively improved using expanded graphite (EG). Existing studies have primarily focused on the effect of the expansion ratio on the cPCMs of SAT, and the effect of the particle size of EG on the cPCMs of the SAT has received limited attention. Additionally, more research is required on the degree of supercooling and effective thermal cycles in thermal cycles. In this study, the effects of EG of different sizes (250 and 425 μm) and proportions (0, 1, 2, 3, 4, 5, and 6 wt %) on the thermal properties and the phase change behaviour of cPCMs in thermal cycles were studied. The results revealed that the 425 μm EG had a better effect on improving the thermal conductivity of the cPCMs, whereas the 250 μm EG had a better effect on improving the thermal cycling stability of cPCMs, as evidenced by the sample with 3 wt% of 250 μm EG completing 512 solidification cycles out of 530 thermal cycles. • Explored expanded graphite's impact on the thermal conductivity and phase change properties of composite phase change materials. • Investigated how expanded graphite influences the thermal cycling stability of composite phase change materials. • Studied expanded graphite's effects on apparent density and rheological behaviour of composite phase change materials. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) present promising solutions for enhancing energy efficiency in solar heat pump systems. In our study, we have innovatively developed a composite PCMs (CPCMs) by combining sodium acetate trihydrate (CH 3 COONa·3H 2 O, SAT), lithium chloride (LiCl), potassium chloride (KCl), and incorporating expanded graphite (EG). This addition of high thermal conductivity EG was aimed at bolstering the CPCM's thermal stability. Our findings reveal that SAT-LiCl-KCl/EG CPCMs, with 14 wt% EG, significantly enhances thermal energy storage performance while preserving the fundamental phase change characteristics. The resulting CPCMs demonstrates a phase transition temperature of 49.3 °C and a latent heat of 196.4 J/g, ideally suited to meet the demands of hot water heat pump systems operating in the 45–50 °C range. Notably, the thermal conductivity of this CPCMs, following the incorporation of 14 wt% EG, registers at 4.54 W/(m K), representing a remarkable 10.6-fold increase compared to the SAT-LiCl-KCl ternary eutectic salt. To ensure long-term stability, secondary encapsulation with a thermally conductive sealant was applied. Subsequent tests involved subjecting the CPCM to 3000 heating/cooling cycles, resulting in minimal deviations, with the phase transition temperature shifting by approximately 1 °C and a modest 6 % reduction in latent heat of phase transition. These outcomes underscore the robustness and reliability of our developed composite phase change materials. • A ternary eutectic phase change material based on sodium acetate trihydrate. • The material melts at 49.3 °C and is more efficient for heat pump systems (45–50 °C). • Secondary encapsulation of composite phase change materials improves its stability. • The material has good thermal properties after 3000 heating/cooling cycles. [ABSTRACT FROM AUTHOR]

A shape-stable glycine water-based phase-change material (GPCM) was fabricated herein via natural adsorption using modified expanded graphite (MEG) as a porous carrier. Cetyltrimethylammonium bromide (CTAB) was introduced as a modifier on the surface of expanded graphite (EG) to synthesise MEG, which improved compatibility between EG and GPCM. Furthermore, the adsorption capacities of EG and MEG on GPCM were compared and analysed. The thermophysical properties of the as-prepared MEG/GPCM composite were evaluated using differential scanning calorimetry. Results revealed that MEG modified with 0.1 g of CTAB (MEG-0.1) had the best compatibility with GPCM and its adsorption capacity increased from 73.96% to 84.05% compared with that of unmodified EG. When the MEG content was 14%, the MEG/GPCM composite had a suitable melting temperature of −5.06 °C and high latent heat of 243.80 J/g. Moreover, the thermal conductivity was 1.836 W/(m⋅K), 216.33% higher than that of GPCM. After 100 thermal cycles, and the melting temperature and latent heat of the MEG/GPCM composite only decreased by 1.38% and 6.15% to −5.13 °C and 228.79 J/g, respectively. Thus, the prepared composites exhibited excellent thermal properties and showed great potential in the application of low-temperature cold energy storage and cold-chain transportation. • The adsorption capacity of MEG increased from 73.96 % to 84.05 % compared with EG. • The compatibility of EG and GPCM was effectively improved by CTAB modifier. • The melting temperature and latent heat were −5.06 °C and 243.80 J/g, respectively. • The thermal conductivity of MEG/GPCM increased by 216.33 % than that of GPCM. [ABSTRACT FROM AUTHOR]

The main research objective of this paper is to develop a low-temperature Eutectic Phase Change Material (EPCM) for use in the Cold Storage Thermal Storage (CETS), with the aim of improving energy efficiency during the cold storage process and addressing energy crises and environmental concerns. In this study, capric acid, n-octanoic acid, and n-tetradecane are prepared as low-temperature EPCMs by melt blending, with the addition of nanographite to enhance their thermal conductivity. The thermal performance parameters, chemical stability, and thermal stability of the EPCMs under phase change cycles are tested and evaluated by using macroscopic experimental methods, DSC, FTIR, and infrared thermal imaging. The research results indicate that the G-2 low-temperature EPCM, prepared by mixing capric acid, n-octanoic acid, n-tetradecane, and nanographite with a mass ratio of 0.231:0.469:0.3:0.06, has optimal thermal properties, specifically including a melting point of 0.32 °C, a melting latent heat of 163.3 J/g, a thermal conductivity of 0.83 W/m·K, and an undercooling of 0.47 °C. These properties make it suitable for cold storage operations. Nanographite can effectively improve the thermal conductivity of EPCM, and a 6 % addition proportion can lead to a 417.45 % increase in thermal conductivity and a 64.39 % decrease in undercooling. However, once the content of nanographite exceeds 6 %, the stability of the EPCM will undergo a significant decline. Furthermore, the results of DSC, FTIR, and infrared thermal imaging confirm that capric acid, n-octanoic acid, n-tetradecane, and nanographite can be effectively co-melted with each other, the heat transfer framework function of nanographite improves the efficiency of latent heat utilization in EPCM, and the G-2 sample maintains acceptable chemical and thermal stability even after undergoing 200 phase change cycles. • A eutectic phase change material (EPCM) was developed using capric acid, n-octanoic acid, n-tetradecane, and nanographite. • The optimal low-temperature EPCM has a phase change temperature of 0.32 °C and a melting latent heat of 163.3 J/g. • The addition of 6 % nanographite in EPCM can lead to an increase in thermal conductivity of 417.45 %. • This new EPCM exhibits acceptable thermal and chemical stability after 200 phase change cycles. [ABSTRACT FROM AUTHOR]

• Studied bulk nanobubbles formation, coalescence, and behaviour in organic host liquids through various gas dissolutions. • N 2 , O 2 and H 2 could form NBs in dodecane, while O 2 could not exist in the form of NBs in isooctane. • CO 2 dissolution notably drops dodecane viscosity, while O 2 dispersion notably raises solution viscosity. • The effect of gas types on the viscosity of the samples is more than the size of the formed NB. • NB-containing samples exhibit higher specific heat capacity, with the greatest enhancement with hydrogen NB. In recent decades, nanobubbles (NBs) have attracted great attentions of researchers in a number of fields, including aquaculture, water treatment, biomedical engineering and energy/power engineering. However, the fundamental understanding of these tiny bubbles through experimental techniques is very challenging. Dodecane, as a phase change material with a high boiling point, and isooctane, as an alternative fuel with high octane number and low volatility, have been researched and used in energy applications. In this work, the nucleation, coalescence and behaviour of formed NBs of carbon dioxide (CO 2), oxygen (O 2), nitrogen (N 2), and hydrogen (H 2) gases in dodecane and isooctane samples as well as their effects on the thermo-physical properties of the samples were investigated by means of molecular dynamics (MD) simulations. The weight fraction of the added gas and temperature were also investigated to understand their effects on the bubble dynamics and inherent properties. The results reveal that the addition of CO 2 gas leads to the biggest drop in the viscosity of the dodecane by 20.47%, while the dispersion of oxygen gas in dodecane increases the viscosity. It is also found that samples containing NBs have higher specific heat capacity than samples without NBs and the highest specific heat capacity improvement can be obtained by dissolving hydrogen NBs. Furthermore, it is found that specific heat capacity of isooctane sample increases by increasing the weight fraction of dispersed gas. However, dodecane shows the opposite trend. By increasing the system temperature, the specific heat capacity of dodecane sample increases while isooctane sample again shows the opposite trend. [ABSTRACT FROM AUTHOR]

Expanded graphite (EG) is often used to encase phase change materials (PCMs) and improve their thermal performance. However, EG's effectiveness when used with disodium hydrogen phosphate dodecahydrate (DHPD) as a hydrated salt is diminished, due to its hydrophobic property. This study proposes modifying the hydrophobic surface of EG with highly hydrophilic nanoparticles, such as SiO 2 and TiO 2 , to address this shortcoming and boost its hydrophilicity. Herein, the nanoparticles were synthesized by the sol-gel technique and mixed with EG to construct a modified EG (MEG). The microstructure, morphology, and adsorption ability of MEG were analyzed. Additionally, the thermal properties, as well as the thermal stability of form-stable composite PCMs, were investigated. The results revealed that by varying the mass ratio of SiO 2 @TiO 2 in MEG, the supercooling degree of the form-stable composite PCMs decreased by 77.36%–78.49%. With 9% SiO 2 @TiO 2 in MEG, the water contact angle of MEG was optimal, and the form-stable composite PCMs prepared (DSMEG3) exhibited a phase change temperature and latent heat of 32.88 °C and 142.13 J/g, respectively. This experimental latent heat was slightly lower than the calculated latent heat by 0.12 J/g. Meanwhile, the supercooling degree decreased to 3.01 °C, and the thermal conductivity increased to 1.23 W/(m ∙ K), which was 1.73 times than that of DHPD. Moreover, DSMEG3 also showed good shape stability, preventing leakage. Therefore, the form-stable composite PCMs, as prepared, are a great potential candidate for the energy storage applications. [ABSTRACT FROM AUTHOR]

Expanded graphite (EG) is often used to encase phase change materials (PCMs) and improve their thermal performance. However, EG's effectiveness when used with disodium hydrogen phosphate dodecahydrate (DHPD) as a hydrated salt is diminished, due to its hydrophobic property. This study proposes modifying the hydrophobic surface of EG with highly hydrophilic nanoparticles, such as SiO 2 and TiO 2 , to address this shortcoming and boost its hydrophilicity. Herein, the nanoparticles were synthesized by the sol-gel technique and mixed with EG to construct a modified EG (MEG). The microstructure, morphology, and adsorption ability of MEG were analyzed. Additionally, the thermal properties, as well as the thermal stability of form-stable composite PCMs, were investigated. The results revealed that by varying the mass ratio of SiO 2 @TiO 2 in MEG, the supercooling degree of the form-stable composite PCMs decreased by 77.36%–78.49%. With 9% SiO 2 @TiO 2 in MEG, the water contact angle of MEG was optimal, and the form-stable composite PCMs prepared (DSMEG3) exhibited a phase change temperature and latent heat of 32.88 °C and 142.13 J/g, respectively. This experimental latent heat was slightly lower than the calculated latent heat by 0.12 J/g. Meanwhile, the supercooling degree decreased to 3.01 °C, and the thermal conductivity increased to 1.23 W/(m ∙ K), which was 1.73 times than that of DHPD. Moreover, DSMEG3 also showed good shape stability, preventing leakage. Therefore, the form-stable composite PCMs, as prepared, are a great potential candidate for the energy storage applications. [ABSTRACT FROM AUTHOR]

Thermophysical properties of molten salts aid in determining the storage efficiency of thermal energy storage (TES) systems in concentrating solar power plants. In this research, a novel ternary molten salt (4NaCl–37KCl–59LiNO 3 , mol%) was utilized as the phase change material (PCM), while Al 2 O 3 nanoparticles (NPs) were employed as a thermal conductivity enhancer. Experimental measurements and molecular dynamics simulations were conducted to confirm that the introduction of Al 2 O 3 NPs as dopants enhanced the specific heat, thermal conductivity, and energy storage density of the eutectic salt. Specifically, at an Al 2 O 3 NP content of 0.5 wt%, the composite PCM exhibited a 44.23 % increase in liquid-state specific heat and a 40.82 % increase in liquid-state thermal conductivity, along with a 15.73 % increase in storage density. This study demonstrates that the enhanced thermal properties of eutectic salts by adding Al 2 O 3 NPs are primarily attributed to the emergence of nanostructures and alterations in atomic potential energy, as evidenced by both experimental and simulated microstructural analyses. These findings offer valuable insight into the selection of thermal storage materials and additives, as well as their implementation in medium-temperature TES systems, with the objective of optimizing the efficient utilization of solar energy. • Eutectic ratios of ternary molten salts predicted by thermodynamic calculations. • Thermophysical properties can be improved by doping with Al 2 O 3 nanoparticles. • The effect of nanoparticle content on thermophysical properties were studied. • Doping with 0.5 wt% Al 2 O 3 nanoparticles achieves a maximum energy storage density. [ABSTRACT FROM AUTHOR]

The purpose of this study is to assess the effect of polyurethane solid-solid phase change materials (PUSSPCMs) and polyethylene glycol (PEG4000) on the thermoregulatory and rheological properties of asphalt, as well as their potential for regulating asphalt pavement temperature. The chemical and thermodynamic characteristics of PEG4000 and PUSSPCMs were investigated using infrared spectroscopy (FTIR), adsorption test, polarized light microscopy (POM), X-ray diffractometer (XRD), differential scanning calorimetry (DSC), thermogravimetric (TG), and atomic force microscopy (AFM). Meanwhile, the effects of PEG4000 and PUSSPCMs on asphalt road performance and micromorphology were determined by tests of thermoregulation, three major indexes, DSR segregation, and scanning electron microscopy (SEM). The results indicate that PUSSPCMs have no hydroxyl characteristic peaks of PEG4000 and isocyanate bonds after the complete reaction. PUSSPCMs exhibit better phase stability over PEG4000, the soft segment for thermal storage changes from crystalline to amorphous and is limited by the hard segment micro-region to maintain a stable solid phase. PUSSPCMs exhibit slightly weaker thermal storage properties than PEG4000, while the thermal stability and elastic modulus are stronger. PUSSPCMs-modified asphalt performs lower thermoregulation properties than PEG4000-modified asphalt, which improves with the increasing soft segments. Furthermore, the advantages of PUSSPCMs-modified asphalt are in terms of basic physical, rheological properties and storage stability. The micromorphology of PUSSPCMs-modified asphalt shows no visible cracks compared to PEG4000-modified asphalt and flattens with soft segment rises, which contributes to the thermoregulation and rheological properties of asphalt. • The phase change behavior, thermal storage properties, and mechanical properties of PUSSPCMs and PEG4000 are investigated. • The thermo-mechanical properties of PUSSPCM and rheological properties of PUSSPCM-modified asphalt are investigated. • The correlation of the thermo-mechanical properties of PUSSPCMs and PEG4000 with the thermoregulation and rheological properties of modified asphalt was analyzed. • Micro-morphological characteristics of PUSSPCMs-modified asphalt and PEG4000-modified asphalt are observed. [ABSTRACT FROM AUTHOR]

Concrete infrastructures, such as high-speed railway subgrades, are vulnerable to frost heave in cold regions. Multi-stage phase change material (PCM) aggregate concrete can alleviate frost heave by thermal regulation. This study explored the effect of replacing coarse aggregate with multi-stage PCM aggregate at 0%− 100% on concrete. Firstly, the compressive strength and splitting tensile strength of PCM aggregate concrete were evaluated. Then, the influence of substituting PCM aggregate on the thermal properties was investigated, including thermal conductivity, thermal diffusivity, volumetric heat capacity, and time-temperature curve. Subsequently, the changes in the pore structure were characterized by using a combination of nuclear magnetic resonance (NMR) and computerized tomography (CT). Finally, the interface transition zone (ITZ) of natural aggregate and PCM aggregate was evaluated by using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results show that the mechanical properties of concrete decrease after the addition of PCM aggregate, but its thermal properties improve. This improvement is not only related to the PCM aggregate but also to the increased pores. It has been confirmed by NMR and CT analysis that the replacement of PCM aggregate leads to an increase in both pore volume and pore number. Only the macropores with a volume larger than 108 μm3 may have an impact on mechanical and thermal properties, although their quantity only accounts for 2%. The SEM and EDS results show that there are no obvious cracks in the ITZ of PCM aggregate, indicating that the PCM aggregate has better compatibility with the cement matrix. Considering the mechanical properties, thermal properties, and porosity, the replacement of 60% PCM aggregate is reasonable in concrete, which provides a theoretical basis for multi-stage PCM aggregate concrete application in cold regions. • The strength of PCM aggregate concrete is descending. • The incorporation of PCM aggregate increases the thermal performance. • The pores increase after the incorporation of PCM aggregate. • A few macropores affect the performance of concrete. • The ITZ of PCM aggregate concrete is not the weakest area. [ABSTRACT FROM AUTHOR]

Incorporation techniques of phase change materials (PCM) in cementitious composites have a significant influence on thermal properties. This study investigated the thermal behavior of low-temperature PCM when subjected to varying temperature change rates and pore confinement inside the porous network of lightweight aggregates (LWA) and encapsulation using melamine-formaldehyde-based polymer. Three categories of thermal energy storage (TES) specimens were prepared: (i) Bulk PCM (i.e., liquid PCM), (ii) micro-encapsulated PCM (MPCM), and (iii) four different LWAs infused with PCM (PCM-LWA). The thermal properties of small-scale individual TES specimens were analyzed using a low-temperature differential scanning calorimeter (LT-DSC) to evaluate the effect of ramp rates. Dynamic vapor sorption (DVS) analysis was utilized to characterize the pore structure of LWAs. LT-DSC results show that undercooling of the PCM significantly increases with the rise in ramp rate for all the specimens; temperature change rate affects the nucleation and crystallization growth process during the phase transition. Pore structure characterization of LWAs indicates that the majority of the pores (> 92 %) were larger than 17.3 nm (i.e., macropores). Confined liquid properties are subjected to modification due to interaction with the confining surfaces, as explained by Gibbs-Thomson theory. PCM incorporated in the LWA porous network experienced variable degree of supercooling during phase transition; magnitude of confinement pressure is dependent on the pore diameter, structure, and tortuosity. Experimental evidence suggested that PCM-LWA will exhibit gradual expulsion of enthalpy of fusion over a larger temperature range (i.e., ∼−5 °C to 4.28 °C) in comparison to MPCM (i.e., ∼4.28 °C). • Effect of temperature change rate on phase transition properties of PCM. • Effect of LWA pore network confinement on phase transition properties of PCM. • Thermal efficiency of latent heat storage specimens. • Correlation of pore size to melting temperature using Gibbs-Thomson theory. [ABSTRACT FROM AUTHOR]

Polyurethane (PU) possesses excellent thermal properties, making it an ideal material for thermal insulation. Incorporating Phase Change Materials (PCMs) capsules into Polyurethane has proven to be an effective strategy for enhancing building envelopes. This innovative design substantially enhances indoor thermal stability and minimizes fluctuations in indoor air temperature. To investigate the thermal conductivity of the Polyurethane-Phase Change Materials foam composite, we propose a hierarchical multi-scale model utilizing Physics-Informed Neural Networks (PINNs). This model allows accurate prediction and analysis of the material's thermal conductivity at both the meso-scale and macro-scale. By leveraging the integration of physics-based knowledge and data-driven learning offered by Physics-Informed Neural Networks, we effectively tackle inverse problems and address complex multi-scale phenomena. Furthermore, the obtained thermal conductivity data facilitates the optimization of material design. To fully consider the occupants' thermal comfort within a building envelope, we conduct a case study evaluating the performance of this optimized material in a detached house. Simultaneously, we predict the energy consumption associated with this scenario. All outcomes demonstrate the promising nature of this design, enabling passive building energy design and significantly improving occupants' comfort. The successful development of this Physics-Informed Neural Networks-based multi-scale model holds immense potential for advancing our understanding of Polyurethane-Phase Change Material's thermal properties. It can contribute to the design and optimization of materials for various practical applications, including thermal energy storage systems and insulation design in advanced building envelopes. [ABSTRACT FROM AUTHOR]

Chemically activated biochar with richer pore structure and higher specific surface area is well suited for loading phase change materials (PCMs). However, the effect of structural characteristics and abundant surface functional groups of chemically activated biochar on the thermal properties of PCMs has not been systematically investigated. Here, shape-stable samples were prepared by introducing biochar obtained by activation with different chemical reagents (ZnCl 2 , H 3 PO 4 , KOH, and K 2 CO 3) into three organic PCMs (paraffin, stearic acid, and polyethylene glycol). The results indicated that the biochar activated by KOH possessed the highest specific surface area of 1344.45 m2/g, followed by biochar activated by ZnCl 2 , H 3 PO 4 , and K 2 CO 3 of 1297.35, 1062.74, and 891.38 m2/g, respectively. The loading capacity of KOH-activated biochar was as high as 82.12 %, 83.13 %, and 80.81 % for the three organic PCMs, and the melting enthalpies of corresponding composite PCMs were 163.82, 168.54, and 139.96 kJ/kg. Additionally, the influence degree on the enthalpies of the three PCMs was only 10.84 %, 12.26 %, and 7.74 %, while that of ZnCl 2 and H 3 PO 4 -activated biochar was as high as 53.61 % and 44.22 %, 52.10 %, and 57.74 %, 55.35 % and 45.79 % indicating the two biochar were not suitable as support materials for PCMs. Moreover, ZnCl 2 -activated biochar has the most apparent upgradation on PCMs' thermal conductivity, which could increase the thermal conductivity of the three organic PCMs by 1.318, 1.34, and 1.229 times, respectively, followed by H 3 PO 4 , K 2 CO 3 , and KOH-activated biochar. • Chemically activated biochar had larger specific surface area. • Encapsulation capacity of KOH-activated biochar for organic were significant. • Influence degree of ZnCl 2 and H 3 PO 4 -activated biochar was obvious. • ZnCl 2 -activated biochar had the most apparent upgradation on thermal conductivity. [ABSTRACT FROM AUTHOR]

Electric vehicles often encounter the challenge of battery capacity reduction in cold environments. Existing thermal conductive patches and partial short-circuiting for electrical heating can address the above issues. In this paper, a method to increase battery capacity was proposed by phase change material (PCM) assisted heating. Specifically, a nitrogen-doped hierarchical porous carbon (NPC) was synthesized through a combination of "low-temperature calcination + concentrated nitric acid treatment" to treat the chrysanthemum-shaped MOF-199@EG, and impregnated with stearic acid (SA) to form a stable composite PCM. With its well-developed pore structure and N-adsorbed active sites, the NPC prevents the leakage of molten SA, maintains stability effect and significantly improves the thermal properties of SA composites. The SA/NPC has a loading rate of 80.15 wt%, closely approaching the theoretical values of latent heat (137.89 J·g-1). It also demonstrates enhanced thermal conductivity (1.873 W·m-1·K-1) and thermal diffusivity (1.024 mm2·s-1). Thermal conductivity and thermal diffusivity of SA/NPC are 8.56 times and 14.06 times higher, respectively, than those of SA. Furthermore, when the lithium-ion battery is discharged 2C at −20 °C, the utilization of SA/NPC as an insulation material can increase the discharge energy by 7.89 %. Consequently, this novel composite PCM holds significant promise for the thermal optimization of batteries at low temperature. • A method to increase battery capacity was proposed by phase change material assisted heating. • A nitrogen-doped hierarchical porous carbon was synthesized. • Novel composite PCMs was used for the thermal optimization of batteries at low temperatures. [ABSTRACT FROM AUTHOR]

• GO reduced supercooling of microencapsulated phase change materials (MEPCMs). • GO further increased the degradation temperature of the microcapsules by 7–21 °C. • Thermal conductivity of MEPCM increased to 1.04 W/m∙K by 0.5 w.t.% GO. • Young's modulus/hardness of MEPCMs increased 0.2/0.1 GPa by 0.5 w.t.% GO. The low thermal conductivity of microencapsulated phase change materials (MEPCMs) limits the latent heat charging and discharging rates for various applications. To overcome this limitation, we prepared MEPCM by co-surfactants of polyvinyl alcohol and high thermal conductivity graphene oxide (GO) through an emulsion polymerization process. Fourier transformation infrared spectroscopy and Raman spectra results verified that GO was successfully added to the MEPCMs' hybrid polymer shell. The core material content of MEPCM and GO/MEPCM was within the range of 78.4 %−91.8 % according to differential scanning calorimetry testing results. According to the comparison of fabricated microcapsule samples, the dosage of 0–0.5 w.t.% GO can reduce the loss of shell monomers and overcome the supercooling and leakage problem of MEPCM. Thermogravimetric results exhibited that the thermal stability of MEPCM samples increased by 66 °C after encapsulation, and this value further increased by 7–21 °C with the addition of 0.1–0.5 w.t.% GO. The thermal conductivity of MEPCM samples increased from 0.32 W/m∙K to 1.04 W/m∙K with a dosage of 0.5 w.t.% GO. Meanwhile, Young's modulus and the hardness of GO/MEPCM samples with 0.5 w.t.% GO increased by 0.2 GPa and 0.1 GPa, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microscopic structure of LA and CuO nanoparticles based CPCM was established. • Thermal properties of PCM were predicted by means of molecular dynamics (MD) simulations. • The microscopic structure evolution and phase transition characteristic of the CPCM were investigated. Lauric acid (LA) based phase change material (PCM) has been broadly used for thermal energy storage, whereas its poor thermal performance limits its practical application. In this paper, the microscale structure of LA as the PCM and CuO nanoparticles based composite PCM was established, the thermal properties including density, thermal diffusion, thermal conductivity, melting enthalpy were predicted by means of molecular dynamics (MD) simulations. The microscopic structure evolution and phase transition characteristic of the CPCM system were observed and investigated by structure snapshots and thermal diffusion behaviors. The addition of CuO nanoparticle makes the self-diffusion coefficient of LA based PCM decreased by 15.13 %, and addition of CuO nanoparticle is an effective way to enhance the thermal conductivity of LA based PCM significantly, and it can lead to a 33.765 % increase on average in thermal conductivity with an addition fraction of 6.86 wt%, the melting enthalpy was decreased by 17.57 %, and possible mechanism was revealed at nanoscale. This study is expected to be helpful for the preparation, performance enhancement and practical application of LA based PCM. [ABSTRACT FROM AUTHOR]