Study On Control Of Fire Smoke Movement In Tunnels By Water Mist Segment

The frequency of tunnel fire is not high comparing with the building fire,but it can easily lead to death group death because of the special geometric structure of the tunnel,the space is narrow and the entrances and exits are small,once the tunnel fire happens,the high temperature smoke from the fire will threaten life with the tunnel,and also affect the tunnel visibility.Therefore,in order to ensure the safe evacuation of personnel in the tunnel fire,the key lies in separating the high temperature flue gas from the fire from the evacuation route and providing valuable time for evacuation.Water mist is a new type of fire fighting method,with high efficiency,less water,no environmental pollution and so on.It is proposed to apply the fine water mist to the tunnel,which will prevent the flue gas from spreading to the tunnel in this paper based on the application of water curtain system in fire isolation in buildings.The fog mist is used to cover the tunnel cross section,blocking part of the spread of high temperature flue gas,and another part of the high temperature flue gas through the water mist will be reduced by the droplet cooling,so as to evacuate people to create a better evacuation environment.The main work and achievements of this paper are as follows:(1)1:3 tunnel test model was established based on the Froude similarity criterion,and tests that studied the effects of ventilation conditions,fine water mist characteristics on flue gas temperature and flue gas flow characteristics were carried out.The results shows that in the natural ventilation,the opening of the water mist resulted in the subsidence of the lower reached of the tunnel and delayed the downstream temperature rise of the tunnel.With the increase of the working pressure and the number of open water mist,the downstream temperature of the water mist decreased and the upstream temperature changes little.In the vertical ventilation,the opening of the water mist reduced its upstream and downstream temperatures,and the downstream temperature of the water mist decreased more than it's upstream.(2)In order to further study the mechanism of the lower temperature of the water mist,the experimental conditions were simulated by FDS.Through the accurate setting of tunnel model boundary conditions and fine droplet characteristics,the experimental conditions of 10 sets of tests were simulated in FDS,the temperature field and the smoke spread in the tunnel were compared with the experiment results.The result of the simulation shows that FDS can reproduce all the conditions of the test in this paper,and to simulate the interaction of droplets with flue gas by using FDS was feasible.The comparison of temperature flow field maps with or without water mist shows that a portion of the smoke near the mist is swept by the buzz,which changed the original direction of the flue gas,so that it did not spread to the downstream of the tunnel.(3)Based on the good reproduction of the test,a part of the working conditions to study the characteristics of water mist on the flue gas characteristics of the impact under the vertical ventilation were added.The results shows that the downstream temperature of the water mist increased as the water mist working pressure,open the number of rows increased.(4)The experimental data and the information on the flow field analysis of FDS shows that the role of suction and cooling effect of the fine mists near the smoke made the temperature decreased of the downstream of the tunnel,and the stronger the role of suction and cooling effect were,the lower the temperature was.