Study On The Temperature And Concentration Diffusion Characteristics Of Water Mist Extinguishing Liquid Fire

Water mist develop rapidly rencent years as halon substitute.However,so far, water mist fire extinguishing mechanism is not entirely clear because of the complicated physical and chemical action between water mist and the fire plume.It is necessary to analyse and study the changement of the fire characteristic parameters under the action of wa ter mist and the impact of water mist characteristic parameters on the efficiency of fire suppression.CFD numerical simulation method can simulate the effect between water mist and the fire plum to optimize water mist fire extinguishing technology.Fluent is used to simulate the smoke diffusion characteristics under the action of the water mist in enclosed spaces.It is concluded that the fluent software can simulate exactly the relationship between water mist and spray flame according to the simulation results.at the same time,it is concluded that the flame temperature fall fast with the effect of water mist,arriving at a certain temperature,then the temperature drop slowly,the oxygen concentrations rise rapidly,some time later,reaching a certain value,carbon dioxide concentration begin to drop rapidly and then level off.fire extinguishing effect is better with the increasing of particle size,the extinguishing effect is best at 300 um,and is worse at 400 um. The higher the water mist mass flow rate,the better the fire extinguishing effect, but there is a critical value is 0.5kg/s,the effect will be worse more than the critical value.the spray cone angle have an impact on fire extinguish effect,it is found that the extinguishing effect is better on angle 60°than on 40°,90°and 120°,extinguishing effect is weaken as the angle increases.at the same time,as the increasing of injection angle,more water mist droplets reach the fire area,having a good fire extinguishing effect.Although horizontal flame are difficult to be extinguished compared with vertical flame,the water mist can effectively reduce the horizontal flame temperature.according to the simulation results,it is concluded that fire heat release rate reduce most,the temperature is the lowest,and the co concentration is the lowest when the water mist is above the flame.in the result,the fire extinguishing effect is the best. the impact of the water mist decreases when it is on the upper left and right of the flame,so it just can control flame instead of putting out a fire. at the same time,the extinguishing effect is better when the fire is in the middle of the two water mist sprayer than is at the bottom of the water mist nozzle angle.To expand the application of water mist,fluent software is used to simulate the process of water mist effect on fire in the subway train to provide theoretical basis for the fire control design in extinguishing fire in a subway train with water mist system. according to the simulation results,it is concluded that the effect of water mist on the spray speed of 20m/s on the fire source,the reduction of the power of the fire source,the reduction of the co concentration is greater than the jet velocity of 10m/s water mist,so the fire effect is better. When water mist is coupled with smoke exhaust facility,the heat release rate and fire root temperature reduce more as the growth of the time. The heating and cooling rate of smoke layer decline with the increasing of wind speed,it is concluded that the effects of the mechanical ventilation can reduce co and other poisonous gases volume fraction due to the water mist working alone.