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 1000–2000 m 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 which are the vertical temperature profiles in the inlet (outlet) pipe and the grout of the DBHE and the corresponding dimensionless form are obtained by deducing and solving the heat transfer models inside the borehole. 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, including the quantity of geothermal water exploitation, the well distance between the pumping well and the DBHE, the DBHE inlet temperature, the DBHE depth, and the flowrate of circulating water. Under the action of geothermal wells, the heat transfer mechanism is changed in the thermal reservoir, and the DBHE heat transfer capacity can effectively enhance while the quantity of geothermal water exploitation increases and the well distance decreases. 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.