Rapid performance prediction model for capillary heat exchangers in subway tunnel linings

Abstract

Subways are typical underground spaces that help alleviate urban traffic problems; however, they also face challenges such as high energy consumption and deterioration of the thermal environment, which can seriously impact their safe and efficient operation. A subway source heat pump system (SSHPS) with tunnel-lining capillary heat exchangers (CHEs) is effective for addressing these issues. Current research has primarily focused on the heat transfer performance of tunnel lining CHEs, yet there remains a dearth of rapid prediction models for their heat flux that are suitable for efficient engineering design. In this study, numerical simulation systems for tunnel lining CHEs in rectangular and circular subway tunnels were established to analyse their heat transfer performance under different design conditions. The results show that the heat flux of flat and circular CHEs installed in tunnel lining ranges from 47.03 to 117.65 W/m2, and from 36.06 to 115.09 W/m2 in the cooling season, respectively. In contrast, in the heating season, the heat flux of flat and circular CHEs ranges from 27.03 to 89.90 W/m2, and from 19.35 to 87.77 W/m2, respectively. Based on the analysis of these results, rapid prediction models for the CHE heat flux were established using multivariate linear fitting. The established models passed a series of statistical tests, indicating high statistical significance. This study provides a theoretical basis for the engineering design and applications of tunnel lining CHEs.