Analytical model of coaxial borehole heat exchanger based on segmentation method

In order to optimize the design of Coaxial Borehole Heat Exchanger (CBHE), based on the segmentation method, an analytical model of the CBHE was proposed. In the analytical model, according to the thermal resistance theory and line-source theory, the internal and external heat transfer models of the borehole were constructed respectively, and the 3D CBHE analytical model was constructed based on the segmentation method and time superposition theory. The calculation results of the analytical model were compared with the numerical analysis results and test resnlts, which verified the rationality of the analytical model. Based on the analytical model, the influence of the non-uniform distribution of soil thermal conductivity on the heat transfer effect of CBHE is studied. The results show that the heat transfer efficiency for soil with homogenization thermal conductivity is higher than that of soil with gradient thermal conductivity, and this tendency increases with the increase of the thermal conductivity change amplitude; which means that the non-uniformity of soil thermal conductivity should be considered when evaluating the heat transfer efficiency of CBHE. © 2022, Solar Energy Periodical Office Co., Ltd. All right reserved.