| For long highway tunnels,the most common ventilation mode is longitudinal ventilation.The high cost,large scale and high operating cost are the problems of ventilation system.Therefore,the selection of ventilation scheme of tunnel should not only meet the ventilation requirements but also install the equipment reasonably to the maximum extent to avoid waste of resources.The structural characteristics of tunnel are completely different from that of highway.When there is a fire in the tunnel,a large amount of smoke can not be directly discharged.A large amount of hot smoke will rapidly increase the temperature and CO concentration of the tunnel,and rapidly reduce the visibility,which poses a threat to personnel safety and tunnel structure.Therefore,the study of tunnel ventilation and fire smoke spread law has far-reaching significance for the selection of tunnel ventilation scheme and the prevention and emergency treatment of tunnel fire.Based on the wulingtou tunnel of Wuhuang Expressway and pyrosim fire simulation software,the paper studies the ventilation and smoke exhaust in normal working conditions of the tunnel.The 300 m tunnel model is established by software,and different power and wind speed of fire source are set up.Temperature,CO concentration,visibility slice and thermocouple are set at longitudinal center,ceiling height,average human eye height and central cross section.The change law of temperature,CO concentration and visibility with the position and time from the center of fire source is analyzed.The main contents and conclusions of this paper are as follows:(1)Under the action of no longitudinal wind,after the fire in the middle of the tunnel,the law of smoke spread in 600 s,the law of temperature field at the longitudinal central plane,eye height and ceiling height of the tunnel,and the law of CO concentration and visibility dividing along the longitudinal direction of the tunnel are studied.It is found that smoke,temperature,CO concentration and visibility are basically symmetrical distribution in the tunnel.The smoke spreads from the center of the tunnel to both ends,and the smoke will fill the whole tunnel in about 400 seconds;The temperature,CO concentration and visibility decrease from the center of the tunnel to both ends.The average temperature at the ceiling height above the fire source center reaches 220 ℃,the average temperature at the eye height reaches 80 ℃,and the CO concentration reaches 800 ppm.(2)According to the length of flue gas countercurrent,the longitudinal critical wind speeds of 5MW,10 MW and 30 MW fire power are 2.5m/s,3.0m/s and 3.5m/s respectively.By comparing the temperature distribution of the same fire power along the tunnel under different longitudinal wind speeds,it is concluded that in a certain range,with the increase of longitudinal wind speed,the temperature in the tunnel is lower.Under the action of each critical wind speed,the temperature at the eye characteristic height in the tunnel is not more than 70 ℃ at 5MW,only the fire source center is more than 70 ℃ at 10 MW,and the temperature in the whole downstream length is more than 70 ℃ at 30 MW.(3)In this paper,five kinds of working conditions are set,respectively,the fire source is located in the upstream and downstream of a group of jet fans,and the fire source is located in the upstream,middle and downstream of two groups of fans,to study the influence of jet fans on the smoke extraction effect of tunnel fire.By analyzing the temperature,CO concentration and visibility in the tunnel under various working conditions,it is found that the best effect of exhaust cooling is when the fire source is located downstream of the two groups of jet fans.Figure[35] table[34] reference[59]... |
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