Numerical Simulation On Fire And Its Interaction With Water Mist In A Room

The danger of fire includes two aspects. Firstly, smoke temperature is very high, and secondly, smoke contains large amounts of toxic and hazardous substances. When fire occurs, space in the room is usually divided into two fields along the height direction, including the smoke layer in upper part and the fresh air layer in lower part. People are radiated by high-temperature smoke and easy to escape when they are under the smoke layer. If people are exposed to high-temperature smoke, they will die in a very short period of time. Studies on characteristics and movement of smoke in the room and then proposing fire fighting strategy has important practical significance. The movement of smoke in the building and the water mist suppression technology are still focuses in fire science and fire engineering. In this paper, characteristics and movement of smoke is simulated through using FDS. Changes of smoke layer height, flue gas temperature, soot density and carbon monoxide concentration are analyzed. The main works and conclusions are as follows:(1) A numerical model on smoke movement in a room is developed based on ISO9705 experiment set-up. The diesel with total fire heat release rates of 60kW is used as fuel. The development of turbulent diffusion flame is simulated by mixture fraction combustion model. It is assumed that the gas behaves as a gray medium. Flame spread and smoke movement are solved through N-S equations with low Mach and variable density. The radiation index of droplet is described by Mie theory.(2) Effects of fire source location on smoke movement is analyzed. The changes of smoke layer height, smoke temperature and soot density are obtained. The results show that fire is closer to opening, smoke layer height is lower. Temperature distribution and soot density is more uniform. When fire is at the corner of room, the smoke layer height is lower. The gradient of changes in smoke temperature and soot density in vertical direction is larger.(3) The impact of opening width and height on smoke movement is simulated. The study draws smoke layer height increases with increasing the opening width and height. Smoke temperature and the gas velocity in opening decrease with increasing width and height of opening.(4) The effects of fire source area on smoke movement is discussed. When fire source area increases, the smoke layer height drops, smoke temperature rises, and the gas velocity in opening increases. (5) Smoke movement in room is studied when sprinkler is installed in different locations, obtaining the variations of smoke temperature, smoke layer height and CO concentration. The results show that the sprinkler far from the opening has better effects on smoke layer rising and smoke temperature and CO concentration decreasing in lower part of room.(6) It is presented that smoke layer height drops with operating pressure increasing. Smoke temperature and CO concentration in lower part of room rise with operating pressure increasing.