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In order to improve the utilization of mine geothermal resource, the casing heat pipe heat exchanger coupled phase change backfill heat transfer system is proposed in this paper. The effects of the number of Casing Heat Pipe Heat Exchanger (CHPHE) on the system temperature distribution, the liquid phase fraction of Phase Change Material (PCM) and the heat storage/heat release performance of system were studied by numerical simulation. The results showed that with increase in CHPHE number, the internal temperature of backfill body increases slowly, and the melting rate of PCM slows down. In the heat storage/heat release coexistence stage, the temperature of backfill body decreases rapidly, and the solidification rate of PCM inside the casing heat exchanger accelerates. When CHPHE number is two, three, and four, the complete melting time of PCM is 2.25 h, 3.16 h and 3.33 h, and the complete solidification time is 1.06 h, 1.20 h and 1.24 h respectively. As CHPHE number increases from two to four, temperature difference between the inlet and outlet CHPHE cooling water during heat storage/heat release coexistence stage decreases from 3.63 °C to 1.63 °C. When CHPHE number increases from two to four, the total heat storage capacity increases from 3320.61 kJ to 3757.88 kJ, and the growth rate is 7.14%. While the heat release capacity increases from 2881.06 kJ to 3110.97 kJ, and the growth rate is 7.98%. However, the more CHPHE number, the greater the thermal interference between heat pipe heat exchangers, and the smaller system energy efficiency coefficient - The energy efficiency coefficient of CHPHE-PCB system will reduce from 86.76% to 82.77% (a reduction of 3.99%) as CHPHE number increases from two to four. The research results obtained in this study can guild the highly efficient exploitation of my geothermal energy.
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