Ceiling heat flux and downward received radiation heat flux induced by weak and relative strong fire plume in ventilation tunnels

The heat flux beneath the ceiling in tunnel fires is an important parameter, which have seldom been reported before in a longitudinal ventilation tunnel. A series of model tunnel experiments were conducted to investigate the ceiling heat flux and downward received radiation heat flux induced by weak and relative strong fire plume in ventilation tunnels. Overall, 96 repeatable test conditions were involved on different heat release rates, longitudinal ventilation velocities and the source-ceiling heights. The correlation for predicting the heat flux distribution beneath the tunnel ceiling is developed based on dimensionless analysis correlation, and the side-walls of the tunnel configuration present are concluded to increase the thermal heat feedback and further increase the ceiling heat flux. For the effect of longitudinal ventilation velocity, the position and value of the ceiling maximum heat flux will be varied with longitudinal ventilation velocity, and the source-ceiling height, the prediction model of the ceiling maximum heat flux under the effect of longitudinal ventilation was proposed. Meanwhile, with the increasing of the longitudinal ventilation velocity, the downward received radiation heat flux first increase and then keep relatively stable.