Heat transfer characteristics of external finned backfill coupled heat exchanger in mine

There are abundant geothermal resources in mine goaf. The effective exploitation of geothermal energy is of great significance to realize the long-term sustainable development of mines. In this paper, a three-dimensional unsteady heat transfer model of a typical serpentine backfill coupled heat exchanger is established using COMSOL Multiphysics simulation software, and the accuracy of the model is verified. A serpentine external finned backfill coupled heat exchanger is proposed. Comparative analysis of the heat transfer performance of serpentine external finned backfill coupled heat exchanger and smooth backfill coupled heat exchanger is conducted. The effects of different fin materials, fin structures and system design parameters on the thermal performance of serpentine external finned backfill coupled heat exchanger are studied. The results show that the temperature difference between the inlet and outlet, total heat storage and total heat release increases with the increase of fin thickness, fin height, and surrounding rock temperature, decreases with the increase of inlet velocities and inlet temperature. The heat exchanger energy efficiency coefficient increases with increasing fin thickness and height, decreases with increasing surrounding rock temperature, inlet temperature and inlet velocities. The temperature difference between the inlet and outlet, total heat storage and total heat release of copper fins are higher than those of other materials. The energy efficiency coefficient of using round fin is higher than that of using square fin, square H-fin and round H-fin. When copper round fins are used, the heat storage of the system is 1457.03 kJ, the heat release is 2831.95 kJ, and the energy efficiency coefficient is 51.45%.