Backlayering distance of thermal fume in tunnel fires (fire experiment using a model tunnel)

Abstract

The backlayering phenomenon is the most important behavior in a tunnel fire. However, the backlayering distance, which is the upwind propagation length of thermal fume, has not been systematically examined so far. The backlayering distance of thermal fume in a tunnel fire was examined by using large-scale model tunnel in this study. Various longitudinal ventilation velocities and four kinds of fire size were set as experimental parameters. The following conclusions were obtained. A new expression was proposed to estimate the non-dimensional backlayering distance L b/H by using the non-dimensional heat release rate Q and Froude number Fr. L b/H = a (Q *1/3/Fr) - b. The included constants a and b in this expression are obtained from experimental data by using the least square method. The proposed expression can predict not only the backlayering distance but also the critical velocity. This expression was applied to the experimental results of other researchers. © 2011 The Japan Society of Mechanical Engineers.