Numerical Simulation on Heat Transfer Performance of Vertical Borehole Heat Exchangers in a Fractured Medium

摘要

Heat transfer performance of vertical borehole heat exchangers (BHEs) is not only influenced by thermal conductivity of the ground, it is also controlled by groundwater flow in areas of significant groundwater movement. An aspect of groundwater flow and heat transfer in a fractured medium is different from that in a porous medium. In this study, numerical model that can simulate temperature changes in and around the BHE with groundwater flow in both porous and fractured media is used to investigate the difference between the performance of BHEs installed in a fractured medium and the performance of BHEs installed in a porous medium. The fractured medium and porous medium have the same hydraulic and thermal conductivity. Simulation results show that performance of BHEs installed at the porous medium is better than that of BHEs at the fractured medium. Temperature of the circulating fluid at the BHE placed at the downstream additionally increases due to the thermal interference of adjacent BHEs, Influence of the thermal interference in the fractured medium is also greater than that in the porous medium.