Experimental and numerical investigation on heat transfer characteristics of vertical ground heat exchangers in karst areas

Heat transfer between the ground heat exchanger and surrounding stratum under the action of ground-water seepage is a potential problem in karst areas, few systematic studies on it have been carried out yet. A model test apparatus was built to experimentally investigate the effects of karst groundwater seep-age and ground stratification on the heat transfer characteristics of ground heat exchangers. The heat and seepage transfer coupling model for ground heat exchangers was established, and verified with the mea-sured data from the model test. Base on the model, the influence of seepage velocity and direction on the heat transfer of ground heat exchangers was analyzed and discussed. Test results show that the seepage can promote the temperature field around the heat exchanger to reach the steady state faster, and the influence of seepage on the soil temperature field around the heat exchanger increases with increasing the seepage velocity. The seepage will carry the heat released by the heat exchanger from the upstream side to the downstream, which effectively reduce the accumulation of heat around the heat exchanger. Soil boundary exists the sudden change of temperature when there are great differences in thermal prop-erties between adjacent soil layers, which can be attributed to the influence of ground stratification. The numerical model proposed in this study can well predict the distribution of soil temperature field around heat exchangers in the model test. Simulation results show that the temperature of soil around the heat exchanger will change along the seepage direction.(c) 2022 Elsevier B.V. All rights reserved.