Experimental study of air curtain thermal insulation efficiency and maximum temperature rise beneath the ceiling under longitudinal ventilation in bifurcated tunnels

Abstract

With the rapid increase in the number of tunnels and the complexity of tunnel structures, tunnel safety has attracted widespread attention from all sectors of society. As a narrow and semi-enclosed space, a fire in a tunnel will cause serious accidental consequences. In this paper, a series of experiments were conducted in a 1:10 reduced-size bifurcation tunnel to investigate the temperature rise distribution pattern of the ceiling in the bifurcation tunnel and the cooling efficiency of the air curtain under the synergistic effect of longitudinal ventilation and air curtain. The reliability of the data was first confirmed by comparing it with the along-travel temperature decay model of Li. At the same time, by analyzing the temperature distribution in the center of the fire source at different air curtain wind speeds, the air curtain airflow could be obtained to contribute to the reduction of the temperature in the center of the fire source. And by analyzing the maximum temperature rise beneath the ceiling in the area on both sides of the air curtain, the effectiveness of the air curtain to insulate and block smoke was investigated. Finally, considering the influence of scale principle on the exit velocity of air curtain, the non-dimensional air curtain velocity was defined, and the prediction model of the maximum temperature rise of bifurcated tunnel ceiling under the synergistic effect of longitudinal ventilation and air curtain was obtained, which was in good agreement with the experimental data.