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This paper presents a comprehensive review of significant studies that are relevant to thermal energy storage technologies using phase change materials (PCMs). The review focuses on the techniques applied to enhance the performance of thermal storage systems and the methods used to analyse the heat transfer problems in PCMs. In addition, this paper reviews the published results and discussions on the heat transfer intensification methods including application of fins, filling materials, nano-fluids, nano-particles, microencapsulation and the thermal conductivity enhancement method. Furthermore, the experimental and mathematical methods to enhance the thermal conductivity of PCMs are summarised, and the methods used to determine the nanofluid dynamic viscosity in recent investigations are also listed and discussed. The focus of this review is to provide a solid basis for the identification of the optimal design for the various heat transfer applications using PCM. [ABSTRACT FROM AUTHOR]

Thermal energy storage is considered as one the most perspective technologies for increasing the efficiency of energy conversion processes and effective utilization of available sources of heat. Advantages and technical attractiveness of the thermal energy storing have resulted in continuously increasing numbers of research activities, especially in the last four decades. Among various applications of thermal energy storage, the heat or cold accumulation in the temperature range from −50 °C to 120 °C has a greater market potential and this can be carried out using a wide range of phase change latent heat materials. Among these materials the salt hydrates deserve a special attention and currently a large number of phase change compositions based on salt hydrates are produced commercially and available on the market. However, reliable data on thermophysical properties as well as their thermal stability over their lifetime is required to build effective storage systems. Currently this data is insufficient and is scattered across numerous sources that are often difficult to access for potential consumers. This paper summarises practically all available original experimental data on the phase change diagram of salt–water systems, melting temperatures, heat of fusion, specific heat, density, thermal conductivity, and thermal diffusivity in solid and liquid states and viscosity in the liquid state for 18 salt hydrates. The above information is provided for major market products on the basis of the salt hydrates for latent heat storage. The wholesale prices for pure salt, salt hydrates, and salt hydrate heat storage compositions are also additionally discussed. [ABSTRACT FROM AUTHOR]

• Solar energy and PCM are used to augment the indoor steam curing process. • Mathematical model of the curing process is developed. • Comparison with experiments confirms the accuracy of the mathematical modelling. • Benefits of the proposed technology are quantitively demonstrated. Steam is used to provide heating and moisture in the curing process for the production of precast concrete (PC) construction elements. The generation of steam requires large amounts of fossil fuels. This study considers the incorporation of solar thermal energy into the steam curing of PC construction elements for reducing the need for fossil fuels and associated CO 2 emissions. For this purpose, the board made of composite phase change material covers the inner surface of the main sun-facing wall in the heating & curing building. The PCM board is heated by sun rays and accumulates thermal energy during the PCM's phase transition, and this energy then is released to the indoor environment of the building, reducing the amount of steam required to maintain a certain level of temperature during the curing process. The energy consumption simulation software, EnergyPlus, and two physical models (built on the scale of 1:3) were used to study the effects of two different PCMs on the thermal performance of such new type of heating & curing buildings. Composite PCMs considered were GH-33 and GH-37 with 33 and 37 °C melting temperatures developed by the research team. The theoretical and experimental results are in good agreement and demonstrate that, compared to the GH-33, GH-37 PCM increases the temperature of the inner surface of the main sun-facing wall and the upper surface temperature of the PC construction element by 3.4 and 1.4 °C, respectively. The heat accumulation and discharge rates also were greater by 62%. For the investigated design of the building and given location in China, the deployment of studied PCM wall panels results in a reduction in the annual energy consumption and CO2 emissions by 58.6 GJ and 5 tons, respectively. The method developed for applying solar energy and selecting PCMs for augmenting steam curing of PC construction elements can be deployed in different geographical regions. [ABSTRACT FROM AUTHOR]

• The laboratory and full-scale prototypes of the novel solar air collector were tested. • Fuel economy achieved in tests varies from 11% to 81% depending on weather conditions. • The increased concentration ratio of about 1.4 was obtained without a sun-tracking device. • The mathematical model of the collector was validated against experimental results. • The model was used to define the rational design parameters of the full-scale prototype. The application of greenhouse technologies is rapidly expanding in China and other regions of the world with the continental climate. Such technologies are characterized by a considerable consumption of fossil fuels, especially in winter periods. Various renewable energy technologies are used to reduce the energy demand in greenhouses, including solar heating. Simpler designs of water or air solar collectors are preferred without sun-tracking devices and reduced dimensions and weight. In this work, a novel solar multi-surface air collector with double-receiver tubes, which does not require a sun-tracking device is proposed and has increased concentration ratio and sun rays convergence and reduced thermal losses. The laboratory and full-scale prototypes of the proposed novel collector were manufactured and tested in laboratory conditions during the December-January period as a part of the greenhouse with the active-passive ventilation wall and latent thermal storage, located in the Beijing Region. Results of experiments demonstrate that the solar collector increases the average temperatures of the greenhouse north wall inner surface by 7.5 °C, indoor air during the night-time by 1.8 °C and indoor soil by 1.5 °C. The novel collector provided active heat gains of 11.831 GJ during the December-January period and satisfied from 11% to 81% of the heat load. A lumped parameter mathematical model of the proposed collector was developed, and the comparison of simulation results and experimental data demonstrate its high accuracy in prediction of the collector performance. The model was used to study the influences of outdoor meteorological parameters, air velocity in the receiver tubes and their length on the performance of the collector. This data was used to determine the rational design parameters and air velocity of the full-scale collector. The model was also used to rationalize the variation of air velocity in the receiver tube during the day. [ABSTRACT FROM AUTHOR]

Prefabricated concrete (PC) components require curing at the specific environment after being cast for the concrete to harden to the required levels over a certain period of time. Currently, steam curing is used as the major technique in concrete production. However, this method is highly energy consuming and requires large amounts of fossil fuels. Analysis of thermal process parameters in PC curing and thermal properties of phase change materials (PCMs), developed by the research team at Beijing University of Technology for the greenhouse applications, resulted in the development of the conceptual design of passive solar PC steam curing buildings with on-wall PCM heat storage. The process of selection of the PCM for installation on the inner surface of the main sun-facing wall of solar passive curing buildings is described. The selection is the result of the evaluation of suitable PCMs using the simultaneous process of transient energy consumption simulation with the deployment of EnergyPlus software and one-dimensional unsteady heat transfer modelling across the thickness of the thermal storage. The EnergyPlus simulations were calibrated against experimental data obtained in the curing building in Hebei Province, China. Theoretical simulations for such the building demonstrate that a GH-37 PCM panel with a thickness of 50 mm is suitable for such the application. The temperature range of phase transition for the GH-37 PCM is between 37.4 and 43.5 °C with latent heat equal to 227.5 kJ/kg. Compared to the same case but without PCM, the monthly and nocturnal average temperature of the inner surface of the main sun-facing wall increases by 1.3 °C and 2.7 °C, respectively. The heating load is reduced by 6.4, 5.8, 3.4 and 2.9 GJ in spring, autumn, summer and winter periods, respectively. The amount of annual steam consumption is reduced by 4.7%. • The design concept of solar-assisted PC curing room with PCM was proposed. • Mathematical model of the PC solar-assisted curing room with PCM was carried out. • The selection of a suitable PCM and its optimal thickness was carried out. • The proposed design solution provides annual energy saving of 4.7%. [ABSTRACT FROM AUTHOR]