Smoke characteristics in tunnel fire interacted with mist of water spray

A series of experiments were conducted to investigate the effect of water spray on the characteristics of fire-induced smoke flow in tunnel. A 1/20 reduced scale tunnel was built with a dimension of 6000 mm length × 640 mm width × 360 mm height. Several parameters were changed in the experiments and quantitative analysis was performed. Smoke temperatures and densities at different locations were measured. Smoke clusters/particles were captured by brass meshes and imaged by Scanning Electron Microscope. The results have indicated that water spray not only can cool the hot smoke by absorption of heat through evaporation of spray droplets, but also remove part of the smoke particles by causing the particles to cling to the water droplets. The temperature measured behind the back of water spray decreased as soon as the water spray was actuated. The maximum temperature was measured to be less than 50°C, which was considered as harmless to the passengers and facilities. The particle removal efficiency increased with the increase of the water spray pressure. The maximum value of removal efficiency could reach to 99.7% when the water spray pressure was set at a relatively higher pressure. The magnitudes of the smoke cluster sizes with the interaction of water spray were 10 times larger than that without water spray. Additionally, the mechanism of smoke particles absorption by water droplets was discussed. A simplified model was presented to predict the absorptions. The critical condition was found to be dependent on the surface tensions of particle/air, particle/water, and air/water. © 2011, Baywood Publishing Co., Inc.