Ice Thermal Energy Storage Systems

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Introduction Many studies on thermal energy storage systems using ice have been reported for load leveling of electric power [1]. In particular, in a dynamic ice thermal energy storage system, cold thermal energy can be transported directly because fluid ice slurry is used as a phase change material. Moreover, ice slurries are applicable for heavy thermal loads because they have high melting heat transfer rate. However, characteristics of ice slurries in fundamental processes including generation, storage, transportation, melting and so forth, have not been described yet. Therefore, ice thermal energy storage systems could be better understood by understanding these characteristics. In the past, storage and generation of ice slurries have been carried out by many researchers. Hirata et al. [2] proposed a method to continuously produce ice slurry using a buoyancy force. Matsumoto et al. [3] used silicon oil and water mixture emulsions as a thermal energy storage material, and could produce ice slurry having high ice packing factor (IPF). Moreover, some authors showed that permeability of an ice/water mixture varied due to storage in water [4]. Melting heat transfer of ice slurry was also investigated [5]. It is necessary to consider not only the fundamental processes but also the thermal properties of ice slurries to develop the best system, and an amount of cold thermal energy must be controlled appropriately, for designing a thermal energy storage system. Sawada et al. [6] attempted to measure latent heat of fusion of ice slurry, but their study was not satisfactory with regards to dilution heat due to variations in the concentration of solutions. Some measurements using differential scanning calorimetry (DSC) have also be... ... middle of paper ... ... 3.1. Effects of dilution heat Concentration of an aqueous solution varies with changes in amounts of ice, when ice melts or solidifies in aqueous solution. Then, variation of effective latent heat of fusion due to dilution must be considered. Therefore, amounts of heat produced by varying concentrations of aqueous solutions were taken from past studies. Ulbig et al. [14] and [15] carried out precise measurements of heat generated when propylene glycol (PG), ethylene glycol (EG) and ethanol (ET) were diluted with water, respectively. Hubert et al. [16] showed heat absorption by infinite dilution of NaCl solution with water, and Khrenova et al. [17] showed heat absorption by infinite dilution of NaNO3 solution. Using these results, heat from mixing or dilution at 25 °C for each solution was approximated using a least squares method as follows, respectively:

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