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DOI: 10.1615/ICHMT.2014.IntSympConvHeatMassTransf.850
pages 1145-1161

Masaki Toyoshima
Living Environment Systems Laboratory Mitsubishi Electric Corporation, Ofuna Kamakura Kanagawa 247-8501, Japan

Seiji Okawa
Department of Mechanical Sciences and Engineering, Graduate School of Science and Engineering, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8552, Japan


Hot water storage tank (for stratified thermal storage) with heat pump draws a lot of attention nowadays due to its high performance. In Japan, reheating of the bath is common, and in this mode, the jet injects horizontally at the middle of the tank. So the temperature distribution of the tank changes complexly with time. Hence the model is needed to simulate the phenomenon, precisely. Additionally, on a process of designing a hot water storage system, it is necessary to simulate temperature distribution quickly, since test run itself is time consuming process. In the past report, visualization experiments were performed using tracer particles and thermo-sensitive liquid crystals. Experiments were also carried out to find the unsteady temperature distribution in a tank when the positively or negatively buoyant jet was injected horizontally in the middle of the tank. A one dimensional model for simulating temperature distribution, "uniformly distributed injection model" was proposed. The model had applicability to a basic initially uniformed tank temperature. But, by considering the actual equipment, there is a temperature gradient around the jet nozzle, and the mixing process is more complicated. In this paper, the model was applied for the case of having a vertical temperature gradient around the horizontal jet height. And a modified model, "non-uniformly mixing model" was proposed, which was considered with a vertically mixing process by applying a cubic function for a mixing region. The mixing region was determined by a buoyancy force and a vortex near the wall. The performance of the model was verified by comparing the results with the unsteady temperature distribution obtained experimentally. The results showed good agreement. Hence adequacy of the model was clarified.

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