Experimental And Numerical Study On The Application Of Water Mist Technology In Tunnel

The tunnel is a long and narrow type of traffic communication channel, which has the characteristics of small space, narrow road, poor ventilation and so on. In the event of fire, smoke will spread quickly and filled with the entire tunnel, and difficult to discharge, such case can cause great harm to the safety of personnel and make huge obstacles to the fighting process.More attention has been paid in the tunnel fire safety. The traditional tunnel fire extinguishing technologies include fire hydrant, fire extinguishing device, water spray fire extinguishing system and water spray extinguishing system. In recent years, water mist fire extinguishing technology has attracted wide attention, and its application in the tunnel has also been concerned. A lot of countries around the whole world have been carried out applying water mist fire extinguishing system to the tunnel experiment, the results of which show that the system can quickly put out the fire in tunnel water mist. Meanwhile, it has the characteristics of less water consumption, and can quickly clean the air and protect the environment when compared with the conventional water spray. This paper works with both numerical experiments and computer simulation of the real fire on the application of water mist fire extinguishing system in the tunnel.1、The fullscale fire tests.In the experimental study, the researches on the effects of wind speed on the fire suppression based on water mist in the tunnel are relatively small. The tunnel fire simulation experiment platform, water mist fire suppression simulation experiments on the roof and bottom two positions respectively. The influence of the wind speed on the tunnel fire temperature, gas concentration and thermal radiation parameter are studied. The fire suppression system, extinguish fire in tunnel fire by water mist, ability to lower the temperature, air purification and isolation near the fire thermal radiation is discussed.The experimental results show that the influence of wind speed on the parameters of the tunnel is divided into the following aspects:(1) In terms of temperature parameter:Water mist applied before the smoke layer in the tunnel temperature distribution showed a high middle and low ends, and with the increasing of wind velocity, the maximum temperature of the smoke layer to move downstream. After applying water mist, the temperature of the smoke layer showed a downward trend, and the most obvious changes occur above the fire source regional place. As the wind speed increases, the average temperature of the smoke ceiling gradually decreases. (2) In terms of gas concentration parameters:Before the water mist, with the increase of wind speed, the decrease of O2 concentration and the change of CO concentration is not obvious; After the water mist, the O2 concentration is quickly recovered to the environmental value, and the peak value of CO concentration as well as the total amount of the total production decreases significantly. (3)In terms of heat radiation flux:When the wind speed under the conditions of this paper the water mist can effectively inhibit the combustion heat of gasoline on a fire, thermal radiation intensity around the scene of the fire decreases rapidly. With the increase of wind speed, the peak value of heat radiation intensity decreases gradually, which demonstrates that ventilation can strengthen the role of the shielding effect of water mist fire heat radiation. Therefore, under the experimental conditions, the ventilation effect of the tunnel is not significantly affected by the water mist fire control effect, it can not only effectively reduce the fire temperature and CO concentration and the thermal radiation intensity, but also promote the O2 concentration rise, slow down the tunnel fire spreading and fire security.2、Numerical simulation researchThrough FDS simulation, this paper makes a research on the effects of water mist control in tunnel effect. Firstly, the grid size is determined and the applicability of the model is verified by reducing physical experiment conditions. Through the description of phenomena simulation analysis, the efficiency of tobacco control of the water mist fire extinguishing system in tunnel safety partition is proved. Then, the smoking control ability of the water mist in the tunnel is analyzed from four aspects, which are the distance between nozzles, the spray flow rate, the spray cone angle and the fire power.Simulation results show that:(1) When the fire safety protection zone of the tunnel length is divided in 20m interval, the water mist fire extinguishing system can control the smoke in the protection area and reduce the harm of tunnel fire to personnel evacuation.Tunnel model is constructed by FDS. in order to simulate different parameters of water mist how to influence its control effect. First, determine the grid size, verify the model by the way of restoring applicability conditions of physical experiments, through the analysis of the simulated phenomenon description, which proved that the water mist fire extinguishing system in the tobacco control function of tunnel safety partition; Then from the nozzle spacing, spray flow rate, nozzle spray cone Angle, comparing the water mist fire power four aspects in the tunnel control ability.Simulation results show that:(1) could be divided into multiple tunnel fire safety reserve of 20 m, simulation results show that water mist fire extinguishing system can smoke control in the protected area, reduce the tunnel fire harm to evacuate. (2) in a simulated conditions, water mist nozzle distance of 1 m and 2 m, CO concentration is low. there is at adjacent reserve breathing smoke layer height can be controlled in more than 4 m, tobacco control is better than 3 m. (3) the greater the water mist spray flow within a certain range the better the cooling effect of fire, smoke isolation effect are more obvious.But when spraying flow l/min increase from 15 to 20 l/min, the water mist isolation of flue gas and the improvement of cooling effect is not obvious, given the problem such as security and water damage, so this paper selected 15 l/min as a best spray flow. (4)when the spray cone Angleincrease to a certain extent, it can expand the protection radius, but can affect the flame area, which is unfavorable to the flame to go around the cooling of the flue gas temperature.Larger spray cone Angle can’t effective separation and absorption flue gas protected areas, so under the condition of the simulation of this paper suggest selecting 60° as ideal nozzle spray cone Angle. (5) the source of power, the greater the effect of the flue gas control water mist, smoke layer height below 1.5 m or adjacent reserve, when the source of power for 10 mw and 20 mw flue gas tunnel easily pose a threat to evacuate safely, so you need to optimize the tunnel safety reserve, the simulation results show that the optimized water mist fire extinguishing system can effectively control power fire smoke.