Enhanced heat transfer performance of a new horizontal buried tube heat exchanger

Horizontal buried heat exchangers cost less than vertical buried heat exchangers, but they need more land area. In order to reduce the required land area of horizontal buried tube heat exchanger, a finned strengthened heat exchanger pipe was designed to enhance the heat transfer performance, and a three-dimensional research model of shallow geothermal utilization system was established in Chengdu area . In this paper, the optimal shape and arrangement of fins are investigated, and the effects of inlet velocity, soil type, ambient temperature and intermittent operation on the enhanced heat transfer performance are studied. The results show that the enhanced heat transfer performance of rectangular fins is the best in the case of horizontal arrangement. The working fluid flow rate should not exceed 0.3m/s.Soil type has a great influence on heat transfer performance. The heat transfer of rock and soil is the largest, the heat transfer of clay is the smallest, but the strengthening effect of clay is the best. The longer the system runs, the obvious the influence of ambient temperature is, and the heat transfer efficiency increases by about 4% when the ambient temperature drops by 5K.