Numerical Simulation And Experimental Study On Heat Transfer In The Aquifers Around Underground Coupled Heat Exchangers

Based on related heat and mass transfer theories of porous medium, the underground temperature field and radius of heat influence in aquifers and clay layers under the same thermal load were compared respectively. The influence of groundwater flow, including different thermal properties and flow velocities, on the heat transfer between underground coupled heat exchanger (UCHE) and the surrounding soil was analyzed. Especially, a novel method for the arrangement of UCHE group in the area with abundant groundwater was presented.Heat transfer capacity of UCHE is important. Through the analysis of thermal response test data in Beijing, in-situ heat injected in summer and extracted in winter were obtained, which provided necessary basis for design of the practical project. Further, based on the cylindrical heat source model, an improved method for the estimation of thermal conductivity of the soil was presented. Experimental results showed that this method had a better accuracy than existed linear heat source method.Based on the above study, a three-dimensioned unsteady heat transfer model of U-type UCHE was established, which took different thermal properties of soil layers and groundwater flow into account. Combined with the above thermal response test, numerical simulation on the variation of the inlet and outlet temperature of the pipe and effective thermal conductivity with operating time was made. Besides, the effects of different thermal properties of the grout, flow velocity in the pipes and groundwater and the thickness of aquifers on the heat capacity of UCHE were analyzed.