受限空间脉冲细水雾灭火数值模拟

为研究脉冲细水雾灭火效果和灭火机理,采用FDS软件对连续和脉冲细水雾熄灭受限空间油盘火进行了数值模拟。通过模拟和理论分析确定了脉冲细水雾周期为8 s开启、8 s暂停,并设置了冷却和窒息两种灭火条件,对两种细水雾熄灭不同尺寸的柴油池火进行了研究。结果表明:连续细水雾无法熄灭直径15 cm和20 cm的小尺寸油盘火,对直径25 cm中尺寸油盘火的灭火机理为冷却,对直径为30cm和35 cm大尺寸油盘火的灭火机理为窒息;脉冲细水雾能够熄灭不同尺寸的油盘火,且灭火效率高,火焰熄灭均发生在喷头暂停喷水期间,灭火机理为水雾蒸发稀释氧气而窒息。

Numerical simulation for the water mist fire-extinguishing performance via the pulsate discharge mode in a confined space

The paper is aimed at making an exploration of the fire suppression performance and mechanism of the water mist in the pulsate discharge mode through the simulated mode to extinguish the oil pool fires in a confined space in FDS codes.The proposed size of the confined space was a 3-D space of 1.5 × 1.5 × 1.5 m3,whereas a water mist nozzle were to be installed in the middle of the roof.The water mist system is supposed to work at an operating pressure of 1 MPa,with its average diameter of droplets being 300 μm.First of all,the pulsate cycle were supposed to be set up in an alternative rate of 8 s on & 8 s off based on a numerical simulation mode,on the fire-extinguishing status-in-situ including cooling and smothering based on a theoretical analysis system.Then,a numerical simulation for different scale diesel pool fires to be wiped off by water mist has been done with the continuous and pulsate discharges to be imitated,including such parameters as the extinguishing time,the temperature distribution,the content concentration rates of O2,H2 O,CO2 to be analyzed and described.The results of our simulated study show that:for the small-scale pool fires in a diameter of 15 cm and 20 cm,it would be impossible for the continuous water mist to.put out the flame,but the pulsate water mist can do it by smothering,in which the concentration rate of O2 may drop to the limited oxygen concentration,while the temperature of the fuel surface should be raised over its flash point when it is used for the flame to be put out.At the same time,for the middle-scope pool fire in a diameter of 25 cm,it would be possible for the continuous water mist to put out a fire by cooling,in which the temperature of the fuel surface should be made lower than its flash point while the concentration of O2 should still surpass the limited oxygen concentration at the time flame extinct,with the extinguishing function of the pulsate water mist being just to be smothering.Nevertheless,for the large-scale pool fires with diameter of 30 cm and 35 cm,both the continuous and the pulsate water mists are in a position to put out a fire through smothering because of the higher oxygen consumption and greater amount of water evaporation to be promoted by the great fire.Therefore,it can be concluded that the pulsate water mist can be used to extinguish fires of different scales in a short period of time at higher efficiency.Thus,in a pulsate discharge mode,flames can be put out during the time spray stops,whose extinguishing mechanism lies in its oxygen dilution due to the evaporation of droplets.