Numerical Simulation On The Variation Of Smoke Characteristics With Water Mist In Cabin Fire

Water mist fire suppression technology has been received considerable attentions by international fire science researchers for the following advantages:no pollution to environment, extinguishing fire quickly, less water consuming and little damage to protected objects. Now investigations on interaction of water mist with fire smoke are underway. A cabin fire model was introduced in this paper for researching the application of water mist in smoke suppression and the influence towards the extinguishing performance of the two factors. So that the designing of water mist system was implemented on the research of interaction between water mist and smoke.With FDS, influence of water mist on the following factors were simulated, e.g., temperature, velocity, concentration and visibility of smoke, and the concentration of CO, CO2 and O2.And the outcomes demonstrated good performance of water mist applied in decreasing smoke temperature and CO/CO2 concentration, increasing O2 concentration and affecting the direction of smoke-flow. There was a hysteresis in smoke characteristic parameters variation in test points in corridor, in comparison with that inside the cabin. Additionally, the smoke would increase the visibility of the upper part of the cabin while decrease that of the sub-aerial part.Varying the diameter of water droplet at 100μm,300μm and 500μm, with the accordingly designed water mist velocity of 2.5m/s,4.5m/s and 6.5m/s, a set of data was acquired on the effect of temperature decrease; and also the data on smoke characteristic parameter change when contact time of water mist were set at 60s,80s and 100s was collected.Evidence showed that comparing the circumstances where droplet diameter were 100μm and 500μm respectively, smoke temperature was found to decrease faster in the 100μm case;while variation of mist flux took mere effect on smoke characteristic parameter.To set the distance of fire brand from nozzle axes as 1.0m,2.0m and 3.0m, the air ventilation velocity ranging between 1.0m/s and 4.0m/s, fire power as 500 kW/m2, 1500 kW/m2,2500 kW/m2 and 5000 kW/m2, and observe the variation of characteristic parameter according to smoke temperature change. And the conclusion is, the smoke temperature would be effectively lowered in a short time when fire brand is right under the nozzle; while when the fire brand was not right under it, the dropping rate of smoke temperature would decrease as the distance between the nozzle axis and the fire brand.In circumstance where air ventilation was applied, the dropping rate of smoke temperature in the area right under nozzle would decrease as the air velocity increased, while in other area which deviated from the nozzle axis, the rate would otherwise increase. When power of the fire source was increased, the smoke temperature would drop faster under the usage of water mist, while the concentration of CO and CO2 would fall and O2 rise, in a more rapid speed.