Research on the effect of ceiling centralized smoke exhaust system with air curtains on heat confinement and plug-holing phenomenon in tunnel fires

Abstract

As tunnel fires can easily cause numerous casualties, this paper proposes a combination of ceiling centralized smoke exhaust and air curtain ventilation to study the temperature distribution characteristics and smoke control effects to assist passenger evacuation and firefighting. Dimensionless Froude number was introduced for a theoretical analysis and a series of CFD simulations. The plug-holing phenomenon in the coupling effect between air curtains and ceiling centralized smoke exhaust systems was investigated by changed the parameters of the heat release rate, the smoke exhaust rate, and the jet velocity of the air curtains. The results demonstrate a mutually reinforcing effect of the combined ceiling centralized smoke exhaust system and air curtains in terms of smoke control. The optimal distance between the ceiling exhaust port and the air curtains is 30 m. The blocked holes in the coupled system are mainly located at the downstream edge of the exhaust port, which directly reduces the smoke exhaust efficiency. The smoke exhaust efficiency is more affected by the smoke exhaust rate variation than by the air curtains velocity. A model was built to predict the smoke exhaust efficiency of the coupled system when the fire source power is 20 MW. We propose a new modified critical Fr number (3.69), which can be used to predict the phenomenon of smoke plug-holing in the coupled system. These results allow the design of a fire protection system for tunnel fires with a high barrier and high smoke exhaust effect, facilitating the safe escape of people and efficient fire rescue in the event of a fire.