Research on heat transfer characteristics and typical parameters sensitivity analysis of the deep borehole heat exchanger combined with the geothermal wells

Based on abundant hydrothermal geothermal resources at the depth of 1000-2000m formation in the basin of the BoHai Bay, the deep borehole heat exchanger (DBHE) combined with the geothermal wells is proposed. According to the modified thermal resistance and capacity model (MTRCM), the heat transfer models inside and outside borehole are established. The transient analytical solutions are obtained by applying Laplace transform method to calculate the vertical temperature profiles in the inlet (outlet) pipe and the grout of the DBHE. The mathematical model and the analytical solutions are validated by the experimental data and existing studied data. This paper utilizes respectively the Matlab2012 and the Feflow7.1 to solve the heat transfer models inside and outside the DBHE. The sensitivity analysis is performed to examine the influence of typical parameters on the DBHE heat transfer characteristics. Under the well distance of 50m, the DBHE heat transfer capacity increases by 29.5% and 42.5% when the quantity of geothermal water exploitation increases from 0m3/h to 75m3/h and 150m3/h respectively. The results show that the heat transfer mechanism is changed in the thermal reservoir, and the heat transfer progress of the DBHE is intensified through orderly regulating the quantity of geothermal water exploitation and the well distance. However, with the change of the quantity of geothermal water exploitation, the growth rate of the DBHE heat transfer capacity reduces and the sensitivity of the change of the typical parameters on the DBHE heat transfer performance reduces.