Heat Extraction Characteristics of Downhole Heat Exchanger with Ground-Water Flow and Phase Change

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A spiral-tube downhole heat exchanger has been proposed to make the best use of geothermal energy in shallow stratum, and the effect of ground-water flow on heat extraction characteristics with a spiral-tube downhole heat exchanger has been investigated by numerical simulation. Moreover, cooling experiments in a porous cavity have been carried out to clarify phase change phenomena such as freezing and solidification with heat extraction from magma. From the present study it was noted that the heat extraction rate increased with increasing ground-water velocity and that the freezing phenomena in a porous cavity intricately changed due to the difference of porosity.