A new model and analytical solution for the heat conduction of tunnel lining ground heat exchangers: Fid-Bau Portal

A new model and analytical solution for the heat conduction of tunnel lining ground heat exchangers

Zhang, Guozhu / Xia, Caichu / Sun, Meng / Zou, Yichuan / Xiao, Suguang

Abstract In order to solve the freezing damage problem of tunnel in a cold region, an innovative tunnel lining ground heat exchangers (GHEs) heating system was introduced in China for the first time and applied to Linchang tunnel in Inner Mongolia. This new-type system utilized the tunnel linings as heat exchanger to extract geothermal energy from the surrounding rock in the middle part of the tunnel so as to heat tunnel lining and the drainage system at the tunnel entrance. As for the thermal analysis and design of it, the classical line heat source model and “hollow” cylindrical heat source model for borehole GHEs are not applicable. Therefore, a new line source model was put forward in this paper, which considered both composite medium and time-dependent boundary conditions. Its analytical solution was obtained using the superposition principle and finite integral transfer method. The calculated results from the new model were validated by the experimental data of thermal response tests. Furthermore, the new model was applied to analyze the impact factors of heat transfer performance for design optimization, including the ground temperature as well as the flow rate and the inlet temperature of heat carrier liquid. It was proven that the new model can provide adequate tools for the design of tunnel lining GHE heating system.

Highlights ► An innovative technology, tunnel lining GHEs was introduced for the first time. ► A new line source model of tunnel lining GHEs was put forward in this paper, ► The calculated results were validated by the experimental data. ► The new model was applied to analyze the impact factors of heat transfer performance.