Thermal and pressure performance of heat collection tube group in backfill body added with phase change material

Combined with the backfill mining, the heat collection tube group (HCTG) in the backfill body can extract geothermal energy, which can effectively alleviate heat damage caused by high ground temperature. This paper takes the HCTG as research object, the temperature, velocity and pressure distribution of the heat transfer fluid (HTF) during the heat release process of the backfill body were analyzed, and the influences of Re, tube diameter, tube spacing and tube arrangement on the performance of the HCTG were discussed. The results show that the heat transfer capacity increases from 2.24×103 kJ to 16.78×103 kJ and the comprehensive evaluation factor increases from 0.087 to 1.31 for Re from 100 to 5000. The heat transfer capacity increases from 15.07×103 kJ to 17.11×103 kJ and the comprehensive evaluation factor increases from 1.157 to 1.388 for tube diameter from 4 mm to 6 mm. The heat transfer capacity increases from 14.24>103 kJ to 16.25>103 kJ and the comprehensive evaluation factor increases from 1.013 to 1.263 for tube spacing from 130 mm to 170 mm. In addition, the four-way parallel arrangement can ensure higher heat transfer capacity and lower pressure drop, and obtain a higher comprehensive evaluation factor. The research provides a theoretical reference for the design and optimization of HCTG in the backfill body.