Performance analysis of capillary front-end heat exchanger for subway tunnel

摘要

The ground source heat pump system can remove the waste heat from the subway tunnel and supply heat to the above-ground building in winter at the same time, which not only alleviates the thermal accumulation of the tunnel surrounding rock, but also effectively utilizes renewable energy. In this study, the heat transfer performance of the capillary front-end heat exchanger for the subway tunnel ground source heat pump system was studied by simulation. The capillary heat exchanger was simplified as a surface heat source, and the one-dimensional unsteady heat transfer model was established by TRNSYS. The heat transfer process between the capillary, the surrounding rock and the tunnel air was simulated. The effect of inlet water temperature, water flow velocity, initial temperature of tunnel surrounding rock and tunnel air temperature on the performance of capillary heat exchanger was analyzed. Based on the actual conditions, the range of the capillary heat flux was given. Besides, the heat transfer performance of the capillary under intermittent operation was studied. It was found that, when the operating time ratio was 2/3, 1/2, 1/3, and 1/6, the heat flux increased by 10.6%, 21.8%, 28.3%, and 36.9% respectively compared with continuous operation.