Study On Smoke Exhaust Effect Of Centralized Smoke Exhaust Mode In Long Highway Tunnel Fire

In recent years,with the rapid development of economy and technology,the number and mileage of highway tunnels have increased significantly.While highway tunnel construction has made remarkable achievements,tunnel fire accidents have also occurred due to various factors,especially in long highway tunnels,once a fire occurs,the consequences are serious.Therefore,fire and smoke control measures for long highway tunnels are becoming increasingly important.In order to solve the problem of smoke exhaust in long highway tunnel fire,a centralized smoke exhaust system with independent smoke exhaust ducts is proposed in the tunnel smoke control and exhaust project.In view of the centralized smoke exhaust mode,the predecessors seldom studied the layout of smoke exhaust valves,the air distribution of exhaust fans at different positions of fire sources and the smoke temperature,air velocity,pressure difference,CO₂ mass flow rate and smoke exhaust efficiency in tunnels and at the smoke exhaust valves at different spacing.Therefore,it is necessary to study the influence of these factors on the smoke exhaust effect of tunnels,in order to provide certain reference and basis for the design of centralized smoke exhaust system in long highway tunnels.Based on the ventilation and smoke exhaust design of Cangling Tunnel in Zhejiang Province,this paper uses FDS?Fire Dynamics Simulator?software to establish the corresponding tunnel geometry model and carry out numerical simulation.The research conditions and results are as follows:?1?There are three types of smoke exhaust valves:one side layout,the middle layout and the two sides layout.For each layout,the smoke spread in the tunnel,the temperature,CO concentration,visibility of eye characteristic height layer,the temperature of partition height layer and the temperature of vault height layer are simulated and analyzed.The results show that the layout on both sides can improve the smoke spread,CO concentration and visibility in the characteristic height layer of human eyes,and still meet the requirements after increasing the power of fire source.?2?When the fire source is located at different positions of the setup segment of the exhaust valve,the influence of different air distribution ratio of the exhaust fan at both ends of the exhaust flue on the exhaust effect is studied.The results show that when the fire source is located in the middle of the setup segment of the exhaust valve,the upstream and downstream exhaust valves are symmetrically opened,and the balanced exhaust mode should be adopted at this time;when the fire source is located at 1/3 of the setup segment of the exhaust valve,the upstream and downstream exhaust valves are asymmetrically opened,and the ratio of the number of openings is 1:2.At this time,the non-balanced exhaust mode should be adopted,and the distribution of the upstream and downstream exhaust air volume is better than that of 2:1-3:1.?3?On the basis of 25m interval of tunnel exhaust valves,increase and decrease the interval of tunnel exhaust valves,and study the temperature of flue gas,air velocity,pressure difference,the quality of CO₂ discharged and the efficiency of exhaust smoke at tunnel exhaust valves.The results show that the distance between the exhaust valves is different,which determines the distance between the exhaust valves and the fire source and the fan,thus affecting the exhaust efficiency of the exhaust valves.When the spacing increases to 30m,the total smoke exhaust efficiency decreases,and individual smoke exhaust valves are in the suction state;when the spacing decreases to20m,the total smoke exhaust efficiency increases,but the efficiency is not improved,so the spacing of smoke exhaust valves is better in 20m-25m.?4?The difference of centralized smoke exhaust mode between one-way and two-way traffic tunnels and the longitudinal smoke exhaust mode under the same working conditions were studied.The results show that the centralized smoke exhaust mode has obvious advantages over the longitudinal smoke exhaust mode.At the same time,under the premise of reasonable centralized smoke exhaust system,when a fire occurs in a two-way traffic tunnel,the problem of smoke exhaust can be solved by evacuating the crowd first and then opening the jet fan to centralize the air supply to the fire source.?5?Finally,a tunnel scale model is built to verify the reliability of FDS software for numerical simulation.