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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]

[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]

Size-controllable 1-octadecanol@polystyrene phase change nanocapsules (NEPCMs) were prepared using the miniemulsion polymerization and dispersed in deionized water containing multi-walled carbon nanotubes to prepare a latent functional thermal fluid (LFTF). The results demonstrate that the NEPCMs exhibit a typical core-shell structure. The average particle size (55.28–143.8 nm) of the NEPCMs can be regulated by controlling the content of compound emulsifiers. The optimal phase change enthalpy has an excellent heat storage capacity of about 222.7 J/g, the encapsulation efficiency is up to 80.63 %, and the average particle size is about 88.3 nm. The heating/cooling cycles results show that NEPCMs have excellent cycle stability. LFTF containing 10 wt% NEPCMs was considered the optimal choice for its excellent photothermal conversion efficiency (up to 64.91 %), excellent dispersion stability (zeta potential 39.17 mV) and thermal storage capacity (peak specific heat capacity 5.72 J g−1 K−1). Under the influence of solar radiation, the temperature rise curve of LFTF exhibited a rapid initial warming rate followed by a plateau period of approximately 76 min upon reaching the melting point of the NEPCMs, whose photothermal conversion efficiency is roughly 2.18 times that of water. The experimental findings demonstrate the potential application of LFTF based on NEPCMs in the solar thermal industry. • Size-controllable (55.28–143.8 nm) NEPCMs (1-octadecanol@PS) were prepared. • The encapsulation efficiency of the NEPCMs reaches up to 80.63 %. • The NEPCMs have excellent thermal storage capacity (222.7 J/g) and thermal stability. • Photothermal conversion efficiency of NEPCMs based LFTF is 2.18 times that of water. [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]

The cost-effective molten chloride salts are promising heat transfer fluids for next-generation concentrating solar plants. However, their limited specific heat capacities and thermal conductivities hinder their applications. In this paper, molten salt-based nanofluids based on a binary chloride (50 mol.% NaCl, 50 mol.% KCl) with Al 2 O 3 nanoparticles were proposed to enhance the thermal properties. Firstly, molecular dynamics simulations were employed to investigate the thermal properties of these nanofluids, focusing on various nanoparticle volume fractions within 1100∼1600 K. The findings reveal that as the nanoparticle fraction increases from 0% to 7%, the specific heat capacity and dynamic viscosity improve by≈14.9% and 34.8%–38.6%, respectively. Concurrently, the thermal conductivity increases by 10.0%–16.5%. Then, microstructure evolution was analyzed to elucidate the enhancing mechanism of the thermal conductivity. Specifically, the negatively charged nanoparticle surface selectively attracts Na+ and K+, resulting in the formation of a compressed layer around the nanoparticle where the short-range order of ions was intensified. As a result, the compressed layer serves as a thermal conduit between the Al 2 O 3 nanoparticle and the surrounding salt, resulting in the enhancement of the thermal conductivity. Furthermore, additional analyses of thermal diffusion properties and energy density distributions provide indirect evidence for the existence of the compressed layer where ionic motion is restricted, further validating the enhancing mechanism. • Nanofluids based on a molten chloride salt and Al 2 O 3 nanoparticles were proposed. • Thermal properties of nanofluids were predicted by molecular dynamics simulations. • Al 2 O 3 nanoparticles can enhance the thermophysical properties significantly. • A compressed layer with high ionic short-range order surrounds the nanoparticle. • The compressed layer can serve as a thermal conduit to improve heat transfer. [ABSTRACT FROM AUTHOR]

The black appearance of asphalt pavement easily absorbs a large amount of solar radiation in hot summer to lower its anti-deformation ability, and asphalt pavement cools down quickly in cold winter to cause cracks. To solve these problems, thermochromic core material (TCM) was encapsulated by the shell material of urea-formaldehyde (UF) resin to prepare thermochromic microcapsule (TM) using situ-polymerization. Then the surface morphology, particle size distribution, chemical composition, phase change property and thermal stability of TM were characterized. After that, emulsified asphalt and acrylic emulsion were selected as film-forming substances to prepare thermochromic asphalt-based composite coating (TACC) after adding different dosages of TM. The surface morphology, chemical composition, thermal storage capacity, phase change property and spectral reflectance of TACC were studied. The results show that TCM is successfully encapsulated by shell material which restricts the thermal conductivity of TCM, making heat transfer process of TM become gentler. Also, the phase change property of TM is still better due to excellent phase change property of TCM. Further, TM particles with the size range of 3.2–4.8 μm are uniformly distributed on TACC surface and show better dispersion in emulsified asphalt. Additionally, TM enhances the thermal storage capacity and thermal stability of TACC. The heat exchange efficiency between asphalt pavement and surrounding environments is increased by added TM particles, improving the thermal stability of TACC. Finally, the increased spectral reflectance in the near-infrared region reflects more solar radiation in hot season because of high reflectivity of TACC on asphalt pavement, which lowers asphalt pavement temperature to improve its anti-deformation ability. [Display omitted] • TACC is developed after adding prepared TM in emulsified asphalt and acrylic emulsion. • The shell material limits thermal conductivity of TCM to enhance thermal stability of TM. • Prepared TM obviously improves thermal storage capacity and thermal stability of TACC. • Heat exchange efficiency between asphalt pavement and environments is increased by TM. • Developed TACC reflects more solar radiations to regulate asphalt pavement temperature. [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]

High-performance thermal storage ceramics can enable utilization of solar thermal power generation plants. In this work, in situ synthesis was used to prepare mullite thermal storage ceramics. Calcined bauxite, talc, and kaolin were used as raw materials. The effects of additives (e.g., SiC, Si 3 N 4 , TiC, and ZrB 2) on the density, mechanical durability, phase components, microstructure, and thermal performance of the mullite ceramics were studied. The results showed that the thermal expansion coefficient, thermal conductivity, and heat storage density of the mullite ceramics were affected by their phase components. SiC and Si 3 N 4 did not decompose during the in situ syntheses, but TiC and ZrB 2 decomposed. With the addition of 10 wt % SiC, the thermal conductivity improved to 2.72 W (m K)−1 (298 K). The heat storage density of this material was 688 kJ kg−1 (273–1073 K). Consequently, the in situ synthesized mullite thermal storage ceramic with added SiC could be a promising candidate material for a compound latent-sensible heat storage system. [ABSTRACT FROM AUTHOR]

• Phase change microcapsules incorporated with the hydroxylated BN were prepared. • The hydroxylated BN showed improved dispersion stability and thermal conductivity. • The microcapsules exhibit a high latent-heat capacity and perfect morphology. • The microcapsules exhibit a reliable and durable heat energy-storage capability. In this paper, phase change microcapsules with excellent performance and stability were synthesized by interfacial polymerization by using tetradecyl octadecanoate (TO) as the core material, isophorone diisocyanate as the shell-forming monomer and modified boron nitride (BN) as the thermal conductive filler. The micro morphologies of unmodified BN, modified BN and different phase change microcapsules were observed by an optical microscope and a scanning electron microscope, and their chemical structures were analyzed through a Fourier transform infrared spectrometer. Meanwhile, the phase change behavior, thermal stability, thermal cycle stability and thermal conductivity of phase change microcapsules were investigated by differential scanning calorimetry, thermogravimetric analysis and thermal conductivity tests. Finally, their exudation stability was tested through leakage experiments. The results show that the spherical TO microcapsules incorporated with modified BN with core-shell structure not only feature a great heat storage capacity (over 150 J/g) and a high encapsulation rate (66.53 %), but also possess excellent thermal stability and thermal cycle stability. After 300 thermal cycles, the phase change peak temperature and the phase change enthalpy value fluctuate within 1.23 °C and 13.76 J/g, respectively. Compared with that of microcapsules without BN, the thermal conductivity of microcapsules incorporated with 3 wt% modified BN increases to 0.1154 W/m·K by 7.95 %. In addition, the microcapsules incorporated with modified BN exhibit prominent exudation stability which enables them to remain intact without leakage at 100 °C for 8 h. [ABSTRACT FROM AUTHOR]

• Thermal properties of a PUSSPCM were improved by adding graphite flakes. • Size effect of graphite flakes on phase change properties of PUSSPCMs was clarified. • Innovatively use a GPCM as solid–solid phase change filler in asphalt mastics. • Effect of the preferable GPCM on rheological properties of asphalt mastics was revealed. • The preferable GPCM had potential to cool asphalt mastics in summer. The goal of this work is to improve the latent heat storage capacity and the thermal response rate of a polyurethane solid–solid phase change material (PUSSPCM) for evaluating its applicability as an alternative filler to cool an asphalt mastic. For this purpose, graphite/PUSSPCM (GPCM) structures with various mesh values and contents of graphite were synthesized. The latent heat was initially increased and then decreased with the increasing graphite content. By selecting the optimum content, a GPCM with a larger mesh can possess a higher latent heat. The existence of a relatively large content and mesh of graphite could lead to a higher thermal conductivity for GPCM. The latent heat storage capacity and the thermal conductivity of the synthesized GPCM-8000–1 were 23.2 % and 254.7 % higher than those of PUSSPCM, respectively. Meanwhile, the GPCM-8000–1 material configuration with excellent thermal stability at 200 °C can withstand the high-temperature construction environment of asphalt pavement without liquid leakage and decomposition. As a result, it is recommended as a solid–solid phase change filler to fabricate phase change asphalt mastics. The extracted outcomes from the rheological test results show that the high-temperature deformation resistance, low-temperature cracking resistance and fatigue resistance of the phase change asphalt mastics are improved in contrast to the traditional asphalt mastic. Finally, the cooling effect of the phase change asphalt mastics was evaluated, with the maximum cooling amplitude reaching the value of 5.6 °C. [ABSTRACT FROM AUTHOR]

• We conduct parametric simulation of pavement radiative and thermal properties. • High solar reflectance reduces urban excess heat during day and night. • Low conductivity and heat capacity reduce urban air temperatures during night. • High conductivity and heat capacity reduce urban air temperature during day. • Effect of highly reflective paving on thermal comfort depends on pedestrian solar reflectance. While pavements are currently a significant contributor to the urban heat island effect, modified pavements could play a role in cooling cities. Specifically, the radiative and thermal properties of pavements can be manipulated to alter the timing and magnitude of sensible heat storage and release into the urban airshed. The present study developed and applied a one-dimensional heat transfer model to Phoenix AZ as a case study to explore the potential for modified pavements in a hot desert climate. We explored solar reflective (0.35 albedo) and traditional (0.10 albedo) asphalt pavements. Pavement thermal conductivity and heat storage capacity values were varied across a reasonable range based on existing products. The results from this study show that daytime peak surface temperature of highly conductive (2.4 WK-1m−1) and thermally massive pavements (4.0 MJK-1m−3) is 17.5 °C cooler than less conductive (0.4 WK-1m−1) and thermally light (1.0 MJK-1m−3) pavements. However, at night, the more thermally massive and conductive pavements were as much as 10.8° C warmer than the less conductive and less massive counterpart. Therefore, when the focus is on reducing excess urban heat during the day, it is better to use pavement materials with higher conductivity and thermal storage. However, when the focus is on reducing the nocturnal heat island, it is wise to use lower conductivity and lower thermal storage pavements. Regardless of thermal properties, the use of reflective pavement surfaces will mitigate both the daytime and nocturnal urban heat island effect. We find up to a 10° C reduction in peak daytime surface temperature and a modest reduction of nocturnal temperatures (by up to 1.0° C) when pavement albedo is increased by 0.25. However, reflective pavements result in a higher influx of net radiation for pedestrians walking on these surfaces during the daytime. So, reflective pavement projects should be evaluated for potential adverse impacts on thermal comfort. Nevertheless, depending upon the time of day and the overall solar reflectivity of pedestrian clothing and skin, we argue that the benefits of reduced surface and air temperatures associated with highly reflective paving likely outweigh the adverse effects for pedestrians. However, for regions where daytime thermal comfort is of primary concern, pavements with higher thermal conductivity and thermal storage may perform better than reflective pavements. [ABSTRACT FROM AUTHOR]

In this article, waste phoenix leaf biochar was introduced into three most used organic phase change materials (PCMs) to prepare shape-stable composite PCMs by the vacuum impregnation method. The encapsulation capacity and encapsulation efficiency of steam activated biochar for paraffin, stearic acid, and polyethylene glycol were 59.28% and 49.14%, 63.03% and 57.62%, 71.38% and 46.84%, respectively, which was related to the mechanisms of biochar encapsulated organic PCMs. The dominant mechanisms of biochar encapsulated organic PCMs are summarized as pore-filling, hydrogen-bonding, hydrophobic interaction between biochar and PCMs, and other potential mechanisms. Influence degree η was introduced to illustrate the effect of biochar on organic PCMs, 16.56%, 8.72%, and 35.75% for steam activated biochar on paraffin, stearic acid, and polyethylene glycol. In addition, compared with original PCMs, the thermal conductivity of biochar-based composite PCMs first decreased and then increased with the increase of biochar pyrolysis temperature. Moreover, biochar-based composite PCMs had better thermal stability, concerned with the dominant mechanisms of biochar encapsulated organic PCMs. Therefore, biochar-based composite PCMs proposed in this study expand the application of biochar and organic PCMs in thermal energy storage, building energy conservation, solar energy utilization, and battery thermal management system. • Some eco-friendly shape-stable composite PCMs were synthesized successfully. •Physically activated biochar had richer structural characteristics than biochar. •The dominant mechanisms of biochar encapsulated organic PCMs were summarized. •The thermal conductivity of composite PCMs was related to pyrolysis temperature. •Biochar-based composite PCM had better thermal stability than original PCM. [Display omitted] [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]

It has been always a daunting task to develop thermal systems with a wide range of thermochemical properties and high stability. It presents a significant challenge, especially when aiming to utilize them for heat storage and transfer applications. In this regard, the thermal characteristics and thermal stability behaviour of molten salt mixture as a heat transfer fluid (HTF) at high temperatures were explored. A novel ternary eutectic salt mixture (base mixture) made of cuprous chloride (CuCl), potassium chloride (KCl) and sodium chloride (NaCl) was investigated as HTF for thermal energy storage (TES) system with a range up to 653 °C in a concentrated solar power (CSP) plant. To extend the temperature span and stability, the effect of an additive was investigated. Different compositions were studied in detail concerning the properties and stability regarding the additive. The molten salt with 7 % CaCl 2 additive improved thermal stability and operating temperature from 653 °C to 700 °C. The transport characteristics and thermal stability of the eutectic mixture with and without the additive were measured by high-temperature thermal analyzers. The results indicated that the melting temperature decreased and the average specific heat capacity considerably increased with the addition of CaCl 2 additive compared to the ternary chloride base mixture. As the temperature increased, the eutectic salt mixture exhibited a reduction in viscosity and density. The viscosity and density of the salt mixture with and without the additive were almost uniform at 700 °C. The average thermal conductivity of the ternary salt mixture with and without additives was 0.72 W/(m°C) which is much more than that of Solar and Hitec salts. In a 100 h experiment of long-period isothermal stability, the eutectic salt mixture showed less than 4 % weight loss at 700 °C. It was defined as the highest operating temperature at which the eutectic salt mixture remained stable. The stability and recyclability of the salt mixture were confirmed through the short-period stability test. The effect of the CaCl 2 additive on thermal stability of base salt mixture was analyzed by X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) techniques. According to the results, this novel eutectic salt mixture had outstanding thermal stability up to 700 °C and could be employed as a viable TES material in CSP plants. • CuCl–KCl–NaCl eutectic mixture with a low melting point (144 °C) and high thermal stability (658 °C) was investigated. • Addition of 7 % CaCl 2 reduced the melting point to 138.3 °C and improved thermal stability to 700 °C. • The proposed salt mixture has an excellent operating temperature range of 200–700 °C. • The long and short period thermal stability exhibited excellent stability and recyclability up to 700 °C. [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]

We use a dual-network model to simulate heat and mass transfer in porous media. The model captures pore-scale information in meter-scale simulations and allows for non-equilibrium between the solid and pore space. We apply the model to predict the effective thermal diffusivity in networks representing Bentheimer sandstone, Estaillades limestone and two random packings of monodisperse spheres. Non-Fourier transport at early times can lead to both higher and lower thermal dispersivity than currently assumed using a volume-weighted average of fluid and solid properties. Furthermore, we quantify the mechanical dispersion coefficient caused by differences in local flow velocity, which further contributes to thermal dispersion of the plume. We discuss the results in the context of the design and management of ATES (aquifer thermal energy storage). Ignoring pore-scale velocity and temperature fluctuations in the estimation of averaged properties can lead to errors of more than 50%. The work provides a framework to predict thermal properties of porous media under different flow conditions for more accurate prediction and design of thermal energy storage. • A dual network model simulated heat and mass transfer with non-equilibrium between the solid and pore space. • Pore-scale fluctuations in temperature and velocity impact averaged thermal transport properties. • Predictions of thermal diffusivity and dispersion can aid the design of subsurface thermal storage. [ABSTRACT FROM AUTHOR]

An optimal design for seasonal underground energy storage systems is presented. This study includes the possible use of natural structures at a depth of 100 to 500 m depth. For safety reasons the storage fluid considered is water at an initial temperature of 90 °C. A finite element method simulation using collected data on the thermal properties of the soil was performed. As a practical example of this methodology, an analysis with data collected in the region of Avila, Spain is made. A temperature-depth map using data measured in the zone was generated. A 3D model of the underground material composition was obtained by electromagnetic field diffusion techniques carried out from the surface. This allows for an analysis of available solutions in energy storage strategies, tailored to the specific conditions on the site with a sufficient degree of precision for a first evaluation without the need for deep excavations. This study shows alternating regions of sands and clays, with natural structures for potential use within a depth of 500 m. Thermal properties of water depending on temperature and pressure are considered. A variety of size configurations shows that, in a cylindrical geometry, a storage system with a radius beyond 2 m does not offer significant benefits in energy stored per mass unit. The benefits of a clay envelope are noticeable, compared with the scenario of a cavity surrounded by sand and followed by clay even after 6 months of storage. According to the underground temperature and the energy needed to transport the storage fluid, it is shown that the thermal performance does not significantly improve between 50 m and 100 m of depth. However, between 100 m and 200 m a noticeable improvement is achieved, and from there down to 500 m the improvement is negligible. Several materials for containing the storage fluid and for thermal isolation are analyzed. For periods beyond 14 days, the thermal properties of thermoplastics are relevant, as found in the case of the Acrylonitrile-Styrene-Acrylate which exhibited the best performance in the simulation. In the best configuration, it is possible to see that by storing water at 90 °C (obtaining 138.78 kJ/kg from an exchange with a typical system at ambient temperature in the months of January–February) compared to the case where the water is stored at the temperature of the underground, that is 25 °C (obtaining 77.08 kJ/kg), it is possible to store 1.8 times more energy per kg of store water without affecting the surrounding medium. Finally, the efficiency of the storage system is calculated from the thermal energy that can be potentially recovered according to the input energy needed to raise the temperature of the fluid from an ambient temperature, up to the initial storage temperature of 90 °C. Due to the thermal properties of clay in the subsoil, previous efficiencies (η = 0. 46) reported in aquifer energy thermal energy storages can be obtained with relatively small storages without continuous energy inlets as is the case of the majority of seasonal thermal energy arranges, with a potential to recover 70% of the inlet thermal energy under optimum conditions of the storage cavity. • Thermal performance of storage with clays improves at depths between 100 m to 200 m. • Water initially at 90 °C recovers 1.8 times more J/kg than that at 25 °C after 6 months. • Storage with a radius beyond 2 m does not offer significant benefits in energy density. • Potential use of natural geological structures with safe energy storage. • Evaluation of energy storage capacity without extensive excavations. [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]

The incorporation of phase change microcapsule (microPCMs) substantially augmented the temperature regulation capacity of foams, endowing it with outstanding application potential in numerous industrial domains. However, interfacial compatibility issues between the capsule and the substrate always exist and affect foam performance. In this study, a milli-meter macrocapsule (macroPCMs) containing microPCMs was prepared using calcium alginate gel as the second layer wall to physically improve the interfacial compatibility. And poly (N-hydroxymethyl acrylamide) was in situ polymerized in the gel layer and provided active alcohol hydroxyl groups to form chemical grafting with the polyurethane raw materials, which further chemically improved the interfacial compatibility. These measures created a significantly improved foam microstructure and a greatly increased foaming capacity, which thus endow the composite foam with excellent thermal insulation performance and mechanical strength. Compared with conventional microPCMs-based foam, the foaming capacity of the macroPCMs-based foam increased by 40 folds, the temperature regulation duration increased by 7 folds, and the mechanical performance increased by 3 folds. Moreover, the insulated incubator fabricated with the macroPCMs-based foam exhibited two-fold greater thermal insulation efficiency than conventional models containing internal ice incubator, which validated the potential of employing macroPCMs-based polyurethane foam in cold chain logistics applications. [Display omitted] • Double-layered macrocapsules with reactive groups on the shell material was synthesized. • The double-layered microcapsules physically and chemically improved the capsules/foams interfacial compatibility. • The improved interfacial compatibility greatly enhanced the macroscopic performances of the composite foams. [ABSTRACT FROM AUTHOR]

Al 2 O 3 ceramics were prepared by introducing Fe 2 O 3 –TiO 2 -Sm 2 O 3 composite additive, in which the content and ratios of Fe 2 O 3 and TiO 2 remained constant, but Sm 2 O 3 was variable. The phase transformation, micromorphology, physical properties and thermal properties were investigated. The results showed that Fe 2 O 3 and TiO 2 made the grains high sintering activity through a solid solution mechanism, which promoted grain growth, but Sm 2 O 3 preferred to form SmFe 4 Al 8 O 19 at the grain boundaries, which slowed grain growth and refined the grains. With the increase in Sm 2 O 3 , the grain refinement of SmFe 4 Al 8 O 19 became outstanding, and the grain diameter gradually decreased, which is favorable for denser sintering. However, only a proper amount of Sm 2 O 3 in the Fe 2 O 3 –TiO 2 -Sm 2 O 3 composite additive resulted in better thermal shock resistance. The Al 2 O 3 ceramics with 9 wt% Fe 2 O 3 -1 wt% TiO 2 -5 wt% Sm 2 O 3 sintered at 1520 °C exhibited the optimum properties, yielding an increase in the bending strength by 6.60% after 30 thermal shocks, a thermal conductivity of 13.33–5.64 W/(m·K) (25–800 °C) and a specific heat capacity of 0.94–1.25 J/(g·K) (25–800 °C), all of which demonstrate the potential for thermal storage. [ABSTRACT FROM AUTHOR]

• Shape-stable attapulgite/capric-myristic acid eutectic mix composite (attapulgite/C-M) was developed. • Attapulgite/C-M was used at 15, 30 and 45 wt% to produce foam concrete. • Solar thermoregulation performances of foam concretes were tested in laboratory and actual ambient conditions. • Foam concretes with acceptable mechanical properties can be used for internal temperature controlling. • Foam concretes save energy in buildings and decrease CO 2 emission. Thermal energy storage (TES) by means of phase change materials (PCM) is of great concern to decrease heating and cooling loads. In building envelopes, one of the most efficient TES methods is integration of PCMs with construction materials for preventing temperature fluctuations by taking advantage of energy storage/release feature of PCMs. Aim of this research was to develop novel foam concretes containing shape-stable attapulgite (ATP) based composite PCM as TES material. Shape-stable ATP/Capric-Myristic acid eutectic mix composite (ATP/C-M) was incorporated into foam concrete at three different ratios (15, 30 and 45 wt%) and characterized. Impacts of ATP/C-M inclusion on physico-mechanic and TES characteristics of foam concretes including composite PCM (FCPCM) were worked systematically. DSC results showed that ATP/C-M composite melts at 22.12 °C with latent heat storage capacity of 74.97 J/g, whereas FCPCM-45 melts at 21.05 °C with latent heat storage ability of 10.98 J/g. Inclusion of ATP/C-M instead of silica sand decreased flow diameter of foam concretes. Compared to reference mixture FCPCM-0, compressive strengths of FCPCM-15, FCPCM-30 and FCPCM-45 samples were reduced in the range of 11–46% while reduction in flexural strength was found to be about 35–57% at 28th day. All FCPCM samples showed lower thermal conductivity values than the specified value and could be defined as better insulation materials. Solar thermoregulation performances of foam concretes containing ATP/C-M were comparatively tested in laboratory and also actual ambient conditions. Results showed that foam concretes with acceptable mechanical properties can be used for internal temperature controlling and energy saving in buildings. [ABSTRACT FROM AUTHOR]

Phase change micro/nanocapsules with high thermal conductivity shells have extensive application prospects in solar energy storage systems and electronics cooling. To improve the heat transfer of the capsules, a method of preparing Ag-shell coated phase change micro/nanocapsules was developed, where the AgBr ultrafine solid particles are introduced to enhance the rigidity of emulsion droplets in the liquid-solid phase transition process, and by employing hydroquinone as the reductant to repeatedly reduce the AgBr that had been adhered to the surface of the emulsion droplets, an Ag shell is formed on the surface of the cores. In this work, palmitic acid (PA) is used as the core material, and the prepared PA/Ag nanocapsules (100–600 nm) exhibit high thermal storage capability and good thermal reliability. The bulk thermal conductivity of the nanocapsules can be as high as 4.072 W/(m·K), indicating that the Ag shell can effectively improve the thermal conductivity of the nanocapsules. Besides, the thermal response of the nanocapsules is estimated by simulating a single-particle heat transfer process considering nanoscale effects, and the results demonstrate that the thermal response time of PA/Ag nanocapsule (350 nm) in working fluid (water, 80 °C) could be as short as 150ns. [ABSTRACT FROM AUTHOR]

The technology of latent heat storage with phase change materials (PCMs) is one of the promising means to improve the utilization of renewable energy. Nevertheless, its broad application will be limited due to the low thermal conductivity of PCMs. In this work, paraffin/expanded graphite (EG) composite PCMs by paraffin having a melting point of 62 °C and expanded graphite with three kinds of particle sizes were prepared and characterized. Environmental scanning electron microscope (ESEM) micrographs showed that EG was dispersed homogeneously in composite PCMs. Meanwhile, the distribution uniformity of expanded graphite in composite PCMs was evaluated quantitatively. The thermal conductivities of composite PCMs increase as the mass fraction of EG increases, and the thermal conductivity of paraffin/EG80 (5 wt.%) was 1.492 W/(m·K) in comparison with the value of pure paraffin was 0.355 W/(m·K). X-ray diffraction (XRD) analysis indicated that the fabrication process of composite PCMs was a purely physical process without a new substance produced. Differential scanning calorimeter (DSC) demonstrated that the latent heat of composite PCM was slightly less than the theoretical value. The addition of EG could lead to the improvement of the melting temperature of composite PCMs, while the decrease of the freezing temperature. [ABSTRACT FROM AUTHOR]

Thermal energy storage using phase change materials (PCMs) plays a crucial role in solving the contradiction between energy supply and demand. In this paper, we proposed a novel approach to design a functionalized process for the matrix which was modified with polydopamine and silver nanoparticles for improving the crystallization process of polyethylene glycol (PEG) PCMs which were bound onto the surface and the interior of the mesoporous silica by adjusting the size and shape of pore systems, the hydrogen bonding force between PEG molecules and carriers. And the results suggested that the prepared supporting materials exhibited prominent chemical compatibility with PEG and a great enhancement for the thermal conductivity (34.0%) with the sequential modification of polydopamine and silver nanoparticles. The composite ss-PCMs also exhibited excellent thermal reliability after 10 thermal cycles, indicating that the emerging composite ss-PCMs had favorable potential in the practical applications. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel LiCl solution for three-phase absorption thermal energy storage is proposed. • The energy storage density of the solution is enhanced by adding two types of additives. • The LiCl crystal slurry overcomes the fluidity problem caused by crystallization. • Thermal and physical properties of the modified solution are measured by experiments. Absorption thermal energy storage (TES) is gaining increasing attention due to its large energy storage density (ESD), mobility and long-term thermal storage capability. Expanding the working concentration difference of a solution can significantly enhance its ESD; however, this may result in crystallization, influencing fluidity and blocking flow channels in a TES device. Furthermore, bulky crystals are difficult to dissolve during energy discharge. In this paper, a novel modified LiCl solution is proposed for three-phase absorption TES, which allows the growth of fine crystals and the formation of well suspended slurry. For the first time, two types of additives with competing mechanism are introduced into the solution: ethylene glycol as a crystallization inhibitor and SiO 2 nanoparticles (SNPs) as a nucleating agent. Compared with traditional working fluids, the proposed solution has a larger ESD and good fluidity. The expanded concentration difference is determined by experiments on solubility and suspension. The optimal mass ratio of the LiCl solution, ethylene glycol and SiO 2 nanoparticles are obtained considering both ESD and fluidity. Heat and cold storage density using this novel LiCl crystal slurry can be enhanced by 24.8% and 156.0% respectively. Measurements on thermal and physical properties including vapor pressure, density and viscosity are also carried out. [ABSTRACT FROM AUTHOR]

This work investigates the combined effect of loading Expanded Graphite (EG) and Expanded Vermiculite (EV) on the thermophysical properties of the low-cost commercially available PCM (OM37) and there capability of regulating the indoor temperature when embedded in the building element. Shape Stabilized Composite Phase Change Material (ss-CPCM) was prepared using PCM, EV, and EG through physical blending followed by vacuum impregnation. Latent heat storage capacity, phase change parameters, melting and freezing response, thermal stability, thermal reliability, and leakage proof performance was investigated. Melting enthalpy of 114.23 J/g, 111.56 J/g, 105.08 J/g, and 99.32 J/g at melting temperature of 40.61 °C, 39.12 °C, 38.83 °C, and 37.41 °C was obtained for ss-CPCM-1, 3, 5, and 7 respectively. A rise of 114.4% in the thermal conductivity was observed by adding 7 wt% of EG in ss-CPCM. ss-CPCM loaded with 7 wt% of EG heats 25.9% faster and cools 19.2% faster in comparison to pristine PCM. The prepared ss-CPCM preserves its thermal characteristics even after 1000 heating and cooling cycles. Moreover, when embedded in the wallboard, the ss-CPCM-7 has shown the excellent capability of regulating indoor temperature. [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]

Thermochemical sorption heat storage based on salt hydrates offers the potential advantages such as high energy density, negligible heat loss, small volume change and flexible working modes. Magnesium sulphate (MgSO 4) is a high energy density hydrated salt available for the thermochemical sorption heat storage. In this work, different types of zeolites (including 3A, 5A and 13X zeolites) have been selected as mass-transfer-enhancing and structural stabilizing materials, and a series of zeolite/MgSO 4 composites have been fabricated. To investigate the thermal energy storage performance of zeolite/MgSO 4 composites, the properties of the composites, such as micro-morphology, pore structure, chemical composition and sorption-desorption behavior, have been characterized and analyzed. Results indicated that the mass transfer performance of the composite materials is significantly better than that of the pure zeolites. As the mass fraction of MgSO 4 in the composite sorbents increases, the specific surface area and porosity of the composite sorbent decreases, and the sorption performance has been enhanced. Compared with 3A zeolite-based and 5A zeolite-based composites, 13X zeolite/MgSO 4 composite materials show the best heat storage performance. At the condition of 25 °C and 60% RH, the 13XM20 has the highest sorption capacity of 0.21 g/g, which is 24% higher than that of pure zeolite 13X. Accordingly, the maximum heat storage density is 438.4 kJ/kg, which exhibits the superior heat storage performance among of the hydrated salt sorbents. The potential of 13X zeolite/MgSO 4 as sorption heat storage material in efficient utilization of solar heat and low-grade industrial waste heat has been revealed. [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]

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]

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]

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]

• 500 °C serves as the threshold for altering the spatial arrangement of limestone. • 500 °C accelerates thermal motion, leading to stratification of rock walls. • Following heat treatment, the microscopic structure displays a 'thousand-layer' pattern. • The thermal conductivity and heat storage coefficient decrease by about 3 % per 100 °C. This article combines X-ray diffraction (XRD) analysis of limestone after high-temperature treatment with microscopic structural characteristics. It aims to elucidate the changes in diffraction peak characteristics from a microscopic perspective and investigate the thermodynamic property variations of the material. The research findings indicate that 500 °C is the threshold temperature at which limestone's crystalline orientation and spatial arrangement change, resulting in a decrease in peak height in the diffraction pattern. Additionally, temperatures ranging from 500 to 600 °C accelerate particle thermal motion, leading to the detachment of rock layers, the inward extension of fissures, and the formation of a sedimentary rock-like 'layered' stacking structure. The thermal conductivity, specific heat capacity, and heat storage coefficient of limestone gradually decrease after thermal treatment, with a reduction rate of approximately 3 % per 100 °C. The microstructural characteristics and thermodynamic property changes of high-temperature limestone reveal the impact of high-temperature damage on limestone structure and thermodynamic properties, facilitating the advancement of limestone material applications and damage control under high-temperature conditions. [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]

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]

[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]

In the field of material science, foaming agents common are commonly used for enhancing the thermal insulation and phase change materials (PCM) for heat storage. However, PCM tends to agglomerate in the cement slurry with the directly addition, presenting an obstacle to effective dispersion. Moreover, the addition of PCM leads to rapid defoaming. To overcome this issue, a novel nanoparticle-stabilized foam was designed in this study to create a three-component system that enhances the interaction of viscosity modifiers, surfactants, and foam stabilizers. The effect of cement density on thermal insulation was evaluated by analyzing thermal conductivity and heat transfer performance tests, as well as exploring the mechanical properties of the cement-based materials. Scanning electron microscope (SEM) images show that the foam designed in this study remarkably promotes the dispersion of PCM microcapsules, indicating the bridging interactions of foam in the cement paste. The result shows that the thermal conductivity of foam cement with 15 vol% PCM microcapsules drops from 0.11 W/m·k to 0.07 W/m·k compared to that without PCM addition, with a dry density around 600 kg / m 3. Furthermore, the specimens with the addition of PCM achieve the endothermic and exothermic peaks under experimental images. This discovery is of great significance to heat absorption ability of low-density concrete, where the addition of PCM leads to a slower foam bursting under the nanoparticle-reinforced foam system. The dispersion and connectivity of foams, as well as the physical characteristics of PCM, provide new perspectives for coexistence in a relatively stable system in this way. • Nanoparticle-stabilized foam remains stable within the cement slurry. • Stable foam contributes to the low thermal conductivity and superior insulation performance of foam cement. • The sustainable and environmentally friendly energy-saving effects of phase change materials microcapsules in foam cement. • A novel lightweight and eco-friendly cement with thermal regulation capabilities. [ABSTRACT FROM AUTHOR]

• Silica aerogel granules were replaced by quartz sand of 0 to 4.5 wt% to produce lightweight cement-based composite mortars. • SAG has increased the water absorption and porosity of the mortar, while reduced compressive strength and hardened density. • Pores increased with increase in aerogel, SAG tend to agglomerate, and pores accumulate around the aerogel particles. • SAG significantly decreased thermal conductivity from 0.772 to 0.155 W/mK. • SAG also reduced thermal diffusivity and heat storage, and increased specific heat. It has been discovered in recent years that the use of silica aerogel in cement-based materials contributes to the thermal insulation properties of the materials, and studies on this subject have gained importance. However, it was determined that the studies mostly remained at the level of the thermal conductivity coefficient and the main physical and mechanical properties of the materials. In this study, a comprehensive research was carried out with the replacement of micro-sized aerogel particles with quartz sand in different ratios (0, 1, 1.6, 2.4, 3.2, 4 and 4.5 wt%) in lightweight cement-based composite mortar (LCCM) combinations. Specifically, the effect of silica aerogel granules (SAG) on flowability, fresh and hardened densities, porosity, water absorption, compressive strength, macro/microstructural properties (by optic microscope, SEM, XRD analysis), thermal conductivity, specific heat, thermal diffusivity and heat storage capability of LCCMs were investigated. While SAG could increase the flowability (up to 8.4 %) at low using rates, it decreased it at higher rates. It is very effective in reducing fresh and hardened densities. However, it highly increased porosity and water absorption, and greatly decreased compressive strength. On the other hand, generally the poor interfacial properties of the cement matrix and the aerogel were moderately improved in this study. The lowest thermal conductivity was determined as 0.155 W/mK in the highest SAG usage. SAG increased specific heat, decreased thermal diffusivity and decreased heat storage capability of LCCMs up to 45.23 %, 63.49 % and 46.32 %, respectively. As a result of the study, aerogel has been identified as a very suitable material that can be used to highly improve thermal properties in LCCMs. [ABSTRACT FROM AUTHOR]

This work concerns the fabrication of a salt based form-stable phase change composite by employing halloysite nanotube (HNT) as ceramic supporting material (CSM). The HNT has been broadly reported for preparation of low-temperature organic composites but very little has been done in medium and high temperature thermal energy storage fields. Herein we demonstrate for the first time with the use of HNT as skeleton substance for the fabrication of salt composite by cold compression and hot sintering technology. The feasibility of material fabrication is confirmed by evaluating a case containing a salt of sodium nitrate as phase change material and HNT as CSM. The effect of preheating treatment of HNT on the microstructure and phase change behaviours as well as cycling performance of the composite is investigated. The results show that HNT can be wetted by the liquid nitrate salt at elevated temperatures, verifying the viability of the present strategy by using HNT as SSM for the synthesis of salt composite. A stable chemical structure is achieved in the salt-HNT composite, which confirms a preeminent chemical stability and compatibility between the HNT and nitrate salt. The hollow tubular structure of HNT could not only be able to provide extra surface for accommodating liquid salt to form a dense composite, but also strengthen the thermal stability of the nitrate salt. The preheating treatment of HNT at 300 °C and 500 °C respectively causes the occurrence of dehydration and dehydroxylation process, which in turn leads to the morphology and microstructure change of HNT, and hence affects the cycling performance of the composite. In comparison with the composite made from HNT preheated at 500 °C where a serious pulverization and deformation has been observed after 100 thermal cycles, the composite containing HNT preheated at 300 °C presents more stable structure and excellent cycling performance, revealing that the HNT is only suitable for the accommodation of inorganic salt that having application temperature limit less than 500 °C. • A form-stable composite containing HNT as CSM and NaNO 3 as PCM is developed. • The feasibility of using HNT as CSM for composite fabrication is evaluated. • Effects of heat treatment of HNT on composite performance is investigated. • HNT is only suitable for accommodating salt having a temperature limit less than 500 °C. [ABSTRACT FROM AUTHOR]

• A promising microfluidic encapsulation technique is proposed. • A novel phase change heat storage microcapsule was developed. • Microencapsulated phase change materials for storage/release of thermal energy such as solar energy. Phase change materials (PCMs), renowned for their exceptional heat storage capabilities, have been extensively utilized in solar energy utilization. However, the persistent challenge of liquid leakage during their use remains unresolved. In this study, a promising microfluidic encapsulation technology is presented, leading to the development of a novel phase change heat storage microcapsule. Differential scanning calorimetry measurements confirm the retention of over 88% of the latent heat of the phase change material (up to 171.8 J/g). Additionally, CFD modeling demonstrates that the geometric structure of the microcapsules significantly enhances heat transfer, effectively addressing the issue of low heat transfer efficiency in PCM systems. Leakage tests have demonstrated the exceptional cyclic stability of microcapsule encapsulation, as it exhibits no leakage even after undergoing 100 consecutive melting-freezing cycles. Moreover, it experiences only a minimal 4.2% loss in latent heat. The incorporation of microcapsule encapsulation into phase change heat storage technology opens up exciting opportunities for harnessing the full potential of phase change materials. [ABSTRACT FROM AUTHOR]

• Maximum improvement of 28.11% is noted in thermal conductivity at 2 wt% of CuO. • Reduction of 11.32% in melting point at 2 wt% concentration of CuO. • Addition of binary mixture of CuO-GnP to paraffin shows improved thermal properties. • 150.69% enhancement in thermal conductivity on addition of CuO-GnP mixture to PCM. This paper presents the experimental investigation on the thermal properties of mono and hybrid nanoPCM. Paraffin wax (PW) as base PCM is doped with CuO nanoparticles and CuO-GnP binary mixture respectively. CuO weight fraction is varied in PW from 0.5% −2.5%. The maximum improvement of 28.11% is noted in thermal conductivity at 2 wt% of CuO. GnP with loading levels of 0.5% − 2% are added to PW having constant wt% of CuO. The maximum improvement of 150.69% in thermal conductivity occurs at 1.5 wt% of GnP. Differential scanning calorimetry analysis shows latent heat and melting point of pure PW is reduced by 3.68% and 11.32% at 2 wt% concentration of CuO. On addition of GnP to the PW/CuO composite, the latent heat and melting point of PW/CuO GnP composite increases upto 1.5 wt% of GnP. Hence addition of CuO-GnP hybrid mixture to paraffin is viable solution for management of thermal energy storage. [ABSTRACT FROM AUTHOR]