Simulation Study On Smoke Blocking Effect Under The Coupling Of Longitudinal Wind And Water Mist

More and more tunnels,corridors and other narrow and long passage spaces exist in many practical projects,convenient but dangerous.Due to its long longitudinal length,small cross-section size and exit at both ends,once a fire occurs,people can only evacuate in two directions,and much toxic and harmful smoke generated by combustion will spread rapidly.There are some defects in the application of current fire separators in the narrow and long passage space,while the water mist system has been widely concerned because of its low cost and clean efficiency.Previous studies on the effect of water mist on smoke control mainly focused on the scrubbing of soot particles and the change of CO concentration at individual observation points near the ceiling.Whether water mist can reduce CO flux has not been reported in literature.In this paper,the water mist curtain was used as the fire-proof separator to study the smoke blocking performance under the coupling effect of longitudinal wind and water mist,especially the inhibition effect of CO flux.In this paper,the numerical simulation method was applied to simulate and calculate under different working conditions,and the smoke spread,temperature distribution and CO diffusion under different conditions were analyzed according to the calculation results,and the smoke blocking effect of water mist,longitudinal wind and the coupling of water mist and longitudinal wind was studied.The main work is as follows:Firstly,the effect of water mist to block CO was studied.The channel model was established by FDS software.The factors such as fire power,water mist particle size and nozzle outlet speed were considered,and 13 working conditions were set up for numerical simulation.The results showed that the application of water mist can prevent the spread of fire to some extent,reduce the temperature under the ceiling,and inhibit the diffusion of CO.With the increase of fire power,the ability of water mist to restrain smoke and reduce ceiling temperature decreased.With the decrease of water mist particle size,the smoke blocking effect,and the ability to restrain CO diffusion of water mist increased.For the same average particle size,the effect of multi dispersed droplet size and single dispersed droplet size on CO suppression and smoke blocking were similar.Even in the early time,the effect of multi dispersed particle size was better.The results also showed that the effect of water mist was better with the increase of nozzle outlet velocity.Then the effect of longitudinal wind to block smoke was studied.Considering the influence of different fire source power and longitudinal wind speed on flue gas,15 sets of working conditions were set up to simulate the fire,and the suppression effect of longitudinal ventilation on flue gas spread in the channel was studied.As the results showed:(1)when the longitudinal wind speed was constant,with the increase of the fire power,the flue gas concentration increased gradually,and the flue gas spread distance decreased gradually.The flue gas layer thickness increased at the outlet of the channel,and the phenomenon of flue gas stratification was weakened.The ceiling temperature increased with the increase of fire source power,and the highest temperature was located in the downwind side of the fire source,and moved to the direction of fire source with the increase of fire source power.When the longitudinal wind is small,the phenomenon of smoke stratification was gradually weakened with the decrease of fire source power.When the longitudinal wind speed is large,the temperature near the fire source was high in the middle of the channel,and the temperature near the top was close to the ambient temperature.(2)When the fire source power was constant,with the increase of the longitudinal wind speed,the smoke spread distance increased,the flame inclination angle increased,the thickness of the smoke layer decreased,and the ceiling temperature decreased gradually,and the highest temperature of the ceiling moved to the downstream of the fire source.When the wind speed was large,the downstream smoke layer was destroyed.Finally,the effect of CO blocking under the coupling application of longitudinal wind and water mist was studied.As the results showed:(1)The original flue gas flow field was destroyed after the application of water mist,and in the early time,the roof flue gas subsided.As time went by,the downstream of the fire source was full of flue gas and the visibility in the channel was low,which was not conducive to the safe evacuation of downstream persons.(2)Under the longitudinal wind,the application of water mist can effectively reduce the temperature of channel ceiling and vertical in the downstream of the fire source.(3)After the application of water mist nozzle,the channel ceiling CO was inhibited in the downstream of the fire source in the early time,but as time went by,the water mist cannot completely inhibit the diffusion of CO to the downstream of the fire source.Because of the role of water mist,the gas circulation was intensified and the mixing of CO and air was increased,which resulted in the disorder of CO distribution and eventually full of the downstream area of the fire source.