Development of a High-Density Exhaust Heat Storage System and the High-Efficiency Utilization

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We focused on a mixture of magnesium nitrate hexahydrate ass base material and magnesium chloride hexahydrate as an additive to store in order to utilize urban waste heat from emerged co-generation systems, typically available at temperatures of 60-90℃ Addition of 5-10 wt% of the latter resulted in a modulated melting point of around 80℃ and a heat of fusion around 150 kJ/kg. Increasing the mix ratio allowed the melting point to be decreased to 60℃, whereas it caused little change of heat of fusion. Repeat tests showed that the heat of fusion and melting point retained their original values after 1000 cycles. Results from corrosion tests showed SUS316 and aluminum can be used as build storage tanks or heat exchangers for the mixture.A high efficient solar hot water supply system with PCM/water hybrid thermal energy storage system was proposed. A demonstration facility which provides 70 evacuated solar collector tubes and a water tank of 250L and a PCM tank of 76L, was constructed. Measurements were reproduced by calculations in terms of minimum points of consumed energy for auxiliary heating. The points existed around 0.3 to 0.4 of the ratio of PCM capacity to total capacity. The solar thermal system could cover 60% of the annual heat demand for hot water supply in Sapporo, Japan Moreover, over 70% of the heat demand can be covered by the system in other southern cities of Japan.Microcapsule Slurry PCM (MCS-PCM) was also applied to the system. The highest performance was shown under conditions with rectangle fins because of the effect of natural convection, whereas round shape fins had the advantage in conditions with a solid PCM. The results of experiments using an actual storage tank showed that 15% larger heat can be recovered in the PCM storage compared to the water storage at the flow rate of 7L/min.