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The issues of inherent low thermal conductivity, slow heat transport rate and easy leakage are critical challenges for accelerating solar-thermal energy harvesting and storage for organic solid-liquid phase change materials (PCMs). Aerogel carriers with thermal conductivity enhancement based on ice temple methods show favorable potential for PCMs solar thermal applications. Comparing with disordered and unidirectional freezing, bidirectional freezing can assemble efficiently in multiple dimensions and result in long-range ordered structures. In this paper, bacterial cellulose/polyvinyl alcohol/MXene aerogels were constructed by bidirectional freezing. The anisotropic PCMs composites were from vacuum impregnation PEG into aerogel networks. By controlling crystallization and growth of ice crystals through the dual temperature gradients, the PCMs composites obtained enhanced heat transfer efficiency in horizontal and vertical directions. Bidirectional aligned PCMs with PDMS wedge angle of 0° and 20° exhibit high thermal conductivity of 0.716 W m−1 K−1 and 0.768 W m−1 K−1, which were 184% higher than that of PEG, and photothermal conversion efficiency of 55.17% and 76.91%. Remarkably, the PCMs composites with a 20° PDMS wedge angle also exhibited a high PCM loading capacity (96.3%) and a high enthalpy (157.7 J/g). The results show that bidirectional anisotropic PCMs composites have excellent overall performance and are expected to improve solar thermal application. • Bidirectional aligned BC/PVA/MXene-PEG PCMs composites were developed. • The assembly of Ti 3 C 2 MXene in long-range oriented structures allows faster heat transfer and enhanced light absorption. • The thermal conductivity of bidirectional aligned PCMs with 20° PDMS wedge angle were 184% higher than that of PEG. • The PCMs composites achieved good photothermal conversion efficiency of 76.91%. • The composites exhibited high PCM loading capacity of 96.3%. [ABSTRACT FROM AUTHOR]

Summary: We investigated the performance improvement of the air‐conditioning system using fumed silica‐based composite phase change materials (PCM). Fumed silica with average particle sizes of 0.007 μm and 0.2 to 0.3 μm and an organic PCM with a phase transition temperature of 18°C were used as the raw materials for the composite PCM formulation. Chemical compatibility between these ingredients, thermal properties, and cyclability of the composite PCMs was studied by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermal hot bridge (THB), and a thermal cycling tester. An in situ X‐ray Diffractometer (XRD) was used to study the congealing behaviour of the PCM composites. The time and efficiency of the charge and discharge processes, and the overall energy efficiency were experimentally studied and compared between the composite PCMs and the pure PCM. The results showed that both the 0.2 to ‐0.3 μm and 0.007 μm silica fumes contributed to the charging rate and efficiency enhancements, while composite PCMs with 0.2 to 0.3 μm silica fumes contributed more to the charging performance improvement. The charging rate, charging efficiency, and overall energy efficiency were observed to increase by 14.67%, 25.82%, and 22.18%, respectively, when the 0.2 to 0.3 μm silica fumes were added into the PCM. The mechanism of the charging enhancement due to the use of silica fumes was also investigated. Novelty Statement: This study investigated the improvement of a PCM for air conditioning application using fumed silica with average particle sizes of 0.007 μm and 0.2 to 0.3 μm. The overall energy efficiency was increased by 22.18% when the 0.2 to 0.3 μm silica fumes were added into the PCM. The mechanism of the charging enhancement due to the use of silica fumes was also concluded. Highlights: New composite PCMs containing silica fumes were developed for air‐conditioning applications.The charging rate was enhanced by up to 14.67% through the composite formulations.The fumed silica with a larger particle size enhances more of the charging kinetics of the PCMs.The overall efficiency of the use of the composite PCMs was improved by up to 22.18%. [ABSTRACT FROM AUTHOR]

Summary This article reports a recent study on a liquid cooling‐based battery thermal management system (BTMS) with a composite phase change material (CPCM). Both copper foam and expanded graphite were considered as the structural materials for the CPCM. The thermal behaviour of a lithium‐ion battery was experimental investigated first under different charge/discharge rates. A two‐dimensional model was then developed to examine the performance of the BTMS. For the copper foam‐based CPCM modelling, an enthalpy‐porosity approach was applied. The numerical modelling aimed to study the impacts of CPCM types and inlet velocity of heat transfer fluid on both the maximum battery temperature and temperature distribution under different current rates. Dimensional analyses of the results were performed, leading to the establishment of relationships of the Nusselt numbers and dimensionless temperature against the Fourier and Stefan numbers. [ABSTRACT FROM AUTHOR]

This review aims to provide an insight into the composite phase change material (CPCM) based battery thermal management system (BTMS), with a focus on the improvement of battery thermal management (BTM) performance using both passive and hybrid BTMS. The mechanism of battery heat generation and temperature effect on batteries are discussed. Challenges of CPCM based BTMS are found to be mainly associated with phase change material (PCM), which has a low thermal conductivity, low form stability, bad mechanical property, and flammability issues for organic PCM. The building of heat conduction paths could effectively increase the thermal conductivity. Discussion on methods addressing this is made, including the incorporation of PCM into porous materials and dispersing thermally conductive nanomaterials within the PCM. The effects of structure/size and surface modification on the thermal conductivity enhancement are analysed. Recent progress in the PCM adsorption into porous materials and melt blending or copolymerizing with polymers have been reviewed. The methods could improve the form stability and increase mechanical property. Formulation of CPCM using flame retardant and inorganic PCMs is found to be promising to address the flammability challenge. Compared with passive cooling, the hybrid BTMS uses active cooling and thus provides a stronger cooling capacity, and the use of CPCM can enhance heat transfer further and provide better temperature uniformity. The review suggests future research focus on developing assembly methods to minimize interfacial thermal resistance, maximising the mechanical property of CPCM, and enhancing the manufacturing readiness of the CPCM based BTMS. • Heat generation mechanisms and temperature effect on LIB introduced. • Challenges of CPCM based BTMS identified and associated solutions reviewed and discussed. • Passive and hybrid BTMS compared based on performance, complexity, and cost. • Insights into further development and commercialisation of CPCM based BTMS provided. [ABSTRACT FROM AUTHOR]

We studied the heat transfer characteristics of a phase change material (PCM) based thermal energy storage (TES) device for transport air conditioning applications. The charging and discharging times and the transient heat flux of the TES device were measured. These data allow quantification of the transient and overall heat transfer coefficients, thus a quantitative comparison between the overall heat transfer coefficients of the charging and the discharging processes. An attempt was made to process the overall heat transfer coefficient data to give the Nusselt number, the Reynolds number, and the Prandtl numbers for both the discharging and charging processes. An empirical relationship between these non-dimensionless numbers was then obtained, which was validated by further experiments. It was shown that the empirical expressions agree with the further experimental data within 2.33% and 1.65% respectively for the charge and discharge processes. To our best knowledge, this study represents the first effort to measure the transient behavior of a PCM based TES device, leading to a set of experimentally validated empirical expressions for the overall heat transfer coefficients. • Study of the transient heat transfer coefficient of a thermal energy storage unit. • The transient charging and discharging heat transfer coefficient was quantified. • The discharging and charging overall heat transfer coefficient was compared. • The empirical equations for the heat transfer coefficient were validated. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) based thermal energy storage (TES) has proved to have great potential in various energy-related applications. The high energy storage density enables TES to eliminate the imbalance between energy supply and demand. With the fast-rising demand for cold energy, cold thermal energy storage is becoming very appealing. In this paper, a review of TES for cold energy storage consisting of various liquid-solid low-temperature PCMs has been carried out. The classification of the PCMs is briefly introduced. Recent approaches to optimizing the properties of PCMs, particularly to remedy the poor thermal conductivity, leakage of liquid PCMs and the high degree of super-cooling, which limits the cold applications of TES, have also been reviewed. Methods for increasing the thermal performance including using composite PCMs and solid mesh are compared. Both modelling and experimental research on cold energy storage devices have been examined. The current cold energy storage applications including air conditioning, free cooling, etc. have been summarised. Compared with previous reviews, this work emphasises the cold energy storage applications instead of the materials aspects. The main challenges and approaches to cold thermal energy storage from the perspective of the engineering applications have been identified. Recommendations for future low charging rates and device design methodology are proposed. • Recent approaches to optimizing PCMs properties have been reviewed. • Both modelling and experimental researches on cold energy storage devices have been examined. • Main challenges and approaches on cold thermal energy storage engineering applications have been identified. • Recommendations on low charging rate issue and device design methodology have been proposed. [ABSTRACT FROM AUTHOR]

This work concerns performance enhancement of phase change material (PCM) based thermal energy storage (TES) devices for air-conditioning applications. Such devices have numerous potential applications in the building environment. The TES device often uses air as the heat transfer fluid and, as a result, its performance is often limited by heat transfer in either or both of the PCM and the air sides. This paper aims to overcome the heat transfer limitations through intensifying heat transfer using two methods of extending heat transfer surfaces (fins) in both the PCM and air sides and adding heat transfer enhancement materials in the PCM. First, a TES device with different configurations (no fins; offset strip fins on the air side only; straight fins on the PCM side only; offset strip fins on air side and straight fins on PCM side) and PCM with different thermal conductivities were modelled and compared. The comparison leads to an advantageous utilization of fins instead of adding thermal conductive particles. The results also indicated a significant extent of performance enhancement of the TES device due to the use of fins with the charging and discharging times reduced respectively by ~85% and ~74%. The airside fins were found to be more effective than the PCM side fins. The results also showed that the heat transfer enhancement due to the PCM side fins could be achieved by increasing PCM thermal conductivity. The modelling results were then validated by experimental data. Finally, a PCM-based TES device was designed and manufactured based on the above results. The device was integrated into an air-conditioning system and experimentally tested. The results showed that, for both charge and discharge processes, the stabilization of the outlet temperature of the air conditioning system was significantly improved, leading to an increased extent of thermal comfort and decreased outlet temperature fluctuations. The obtained results can be used as the design guideline of the compact TES device for air conditioning. Image, graphical abstract [ABSTRACT FROM AUTHOR]

This paper concerns the development of a metal composite containing aluminium as phase change material (PCM) and alumina as structural supporting material (SSM) by the cold compression-hot sintering (CCHS) approach. The microstructural characteristics, thermal and mechanical properties and thermal performance of the proposed composite are characterized. For comparison, a salt composite made of NaLiCO 3 as PCM and MgO as SSM with the same melting temperature as the proposed composite is also prepared and investigated. The results indicate that the alumina is wettable with liquid aluminium at elevated temperature, establishing confidence in fabrication of such aluminium composite through CCHS technique. The composite has good chemical compatibility with the melting temperature around 660 °C, and 45% alumina gives the composite optimal formulation at which a thermal conductivity of 3.75 W/m·K, a mechanical strength of 33 MPa and a thermal energy storage density of 400 kJ/kg over temperature range of 500–700 °C can be achieved. The results also indicate that the aluminium composite presents a higher thermal performance than the salt composite. At the same working conditions, the aluminium composite thermal conductivity is over twice as high as that the salt composite while maintaining a similar thermal energy storage density with salt composite. • An aluminium based form-stable composite PCM was prepared by CCHS approach. • Thermal properties of the composite was compared with a salt based composite. • Proposed composite achieved better performance than the salt composite. • 45% SSM gave composite best combination of thermal and mechanical properties. • Proposed composite can be a promising alternative for high temperature TES. [ABSTRACT FROM AUTHOR]