Resistance-capacitance model of the capillary heat exchanger in subway tunnels

Abstract

The subway operation generates a large amount of waste heat, which will lead to a disruption of the underground thermal balance. To remove the heat, a ground source heat pump system adopting capillary net as the front-end heat exchanger can be built in the tunnels to recycle the waste heat and use it for building heating. Different simulation method was used to analyze the heat transfer process in the tunnel and the surrounding rock. The existing simulation method usually takes a long time for calculation and can not be used for a real-time regulation of the system. Based on the concept of thermoelectric analogy, a resistance-capacitance (RC) model was proposed for rapid prediction and analysis on the heat transfer of the capillary net in subway tunnel. The annual thermal response in the tunnel was analyzed, and the influence of the tunnel air temperature and the capillary inlet water temperature was examined using this model. The maximum heat transfer flux of the capillary in summer (release heat) and in winter (extract heat) was 55.27 W/m2 and 38.33 W/m2, respectively. The effect of capillary inlet water temperature was more remarkable than that of the tunnel air temperature on the capillary heat exchange process.

Keywords

• Subway tunnel
• Heat pump
• Capillary heat exchanger
• Resistance-capacitance model