Numerical simulation of spiral buried pipe heat exchangers applied to annular uniformly distributed pile groups

By the method of numerical simulation, studies the effects of fluid velocity, inlet water temperature, spiral pipe diameter and pitch size on the outlet water temperature and heat transfer of pile-foundation buried pipe heat exchangers and the dynamic distribution characteristics of surrounding soil temperature. The results show that the heat transfer capacity of pile-foundation buried pipe heat exchangers increases firstly when the fluid velocity increases and then decreases when the fluid velocity exceeds a certain point. When the inlet water temperature is 32.5 to 35.0  ℃, the heat transfer is almost linearly proportional to the inlet water temperature, and the higher the inlet water temperature, the higher the heat transfer capacity. The heat transfer capacity of pile-foundation heat exchanger with spiral pipe diameter of 32 mm is 5.8% higher than that of pipe diameter of 25 mm. The heat transfer capacity of the pile-foundation heat exchanger with a pitch size of 500 mm is 1.7 times higher than that with 300 mm pitch size and 1.2 times higher than that with 400 mm pitch size, which indicates a significant enhancement of heat transfer efficiency.