Numerical investigation on the heat storage/heat release performance enhancement of phase change cemented paste backfill body with using casing-type heat pipe heat exchangers

Cemented paste backfill mining technology that recycling tailings and waste rocks can effectively reduce heat damage. Heat pipe exchangers, demonstrating much higher thermal conductivity than water pipe exchangers, led to the development of a novel phase change backfill body system with a built-in casing heat pipe exchanger (HP-PCB). Numerical analysis revealed that, for the melt and solidification of a large amount of PCM, the temperature step phenomenon was observed at both heat storage and heat storage/heat release coexistence stages. Increased surrounding rock temperatures enhanced heat storage and heat release capacities, but reduced system energy efficiency. The optimal water flow velocity was identified at the laminar-turbulent transition flow rate, 0.32 m/s. An increase in water inlet temperature resulted in lower heat release capacity and system energy efficiency. The energy efficiency of the HP-PCB system exceeded that of the traditional water pipe-backfill system by 37.22%. At a surrounding rock temperature of 45 °C, cooling water velocity of 0.32 m/s, and a 6 °C inlet water temperature, the HP-PCB system achieved its highest energy efficiency coefficient, 86.38%. These findings highlight the HP-PCB system potential for efficient geothermal energy extraction in mine.