Study of the convection heat transfer law and temperature prediction of the duct in high-temperature tunnels

Abstract

During the construction of tunnels subjected to high temperatures (here called high-temperature tunnels), ventilation cooling is an essential requirement. A high-temperature section of a construction tunnel on the Sichuan-Tibet Railway was used as a test case to study the heat exchange on both sides of the ventilation duct during active cooling. We used theoretical analysis and numerical simulation to establish a model for calculating the temperatures associated with the ventilation duct, and studied the influence of different factors on the convection heat exchange on the inside and outside the duct during the ventilation cooling process. According to simulation and field measurement results, the airflow temperature inside the duct rose with the distance from the inlet, and the temperature near the duct's wall was higher than the temperature in the center. After analyzing different influencing factors, it was found that duct material and thickness have little effect on the convection heat transfer inside the duct. But the convection heat transfer intensity would rise when the temperature difference between the inside and the outside of the duct increased, and the heat flux ( q ) through the wall increased by 1.5 W/m 2 . The average air temperature trend of the ventilation duct section was stable as the ventilation distance increased. It increased linearly as ventilation distance increased. While the effect of ventilation cooling gradually declined, and the overall temperature of the air of the tunnel rose when the ventilation distance increased. As a result, heat exchange along the duct should be fully considered in the design and application of the ventilation cooling process to ensure that the airflow temperature reaching the excavation face at the head of the tunnel meets the operational requirements.