Numerical study on airflow temperature field in a high-temperature tunnel with insulation layer

Comprehensive understanding of the airflow temperature field in a high-temperature tunnel is critical for the deep underground engineering project. In this paper, we establish a two-dimensional axisymmetric model coupling the convective-conduction heat transfer based on the k - epsilon turbulence equation, by which the airflow temperature field in a high-temperature tunnel for geothermal mining is investigated. We compare the airflow temperature variation with or without thermal insulation layer (TIL) and introduce the valid ventilation distance (VVD) to quantify their differences. The sensitivity analysis of critical factors on the airflow temperature are also examined. We find that (1) the TIL has a remarkable insulation effect even in a high-temperature tunnel, and its insulation effect can be well quantified by the VVD; (2) the TIL insulation effect decreases dramatically as the rock temperature increases, resulting in an exponential decay in the VVD; (3) changing critical factors are effective for reducing the air temperature and increasing the VVD, but these impacts decrease rapidly as the rock temperature grows; (4) the established empirical formula facilitates the VVD estimation and favors parameter optimization in high-temperature tunnels of deep underground engineering projects.