Study On Temperature Distribution And Movement Law Of Smoke From Double Fires In Tunnel

Over the past few years,the density of the road network has been increasing,thereby stimulating greatly development of China’s transportation industry.However,traffic safety is confronted with a really severe situation as the traffic lines are increasing constantly.To be specific,The tunnel safety issues are particularly striking.Due to its unique long and narrow characteristics,Once a vehicle is in an accident and catch fire in the tunnel,there will be less oxygen,more toxic fumes and less visibility,making it difficult to evacuate people.Meanwhile,the longitudinal exhaust ventilation system and ceiling smoke exhaust system under the ceiling play a prominent part in controlling the plume spread movement and temperature change.This paper mainly studies the temperature distribution and movement regular of the smoke from the double fires in the tunnel,based on double tunnel fires,The maximum temperature and longitudinal temperature decay mechanism were studied by means of scaling experiment and theoretical analysis under the condition of natural ventilation and ceiling exhaust.The smoke back-layering length and critical velocity of smoke movement are revealed under the longitudinal ventilation tunnel,and verify the effectiveness of the tunnel smoke extraction mechanism.The main research contents of this paper are as follows:In this paper,the longitudinal temperature decay and maximum temperature rise of double fires in the tunnel under the condition of natural velocity are studied by small size experiment.It is found that without longitudinal velocity,the maximum temperature under the tunnel ceiling decreases with the increase of distance between double fires,and the dimensionless temperature rise shows exponential decay under fixed ignition power.The prediction models of the maximum temperature and the longitudinal attenuation under the natural ventilation tunnel are established.Secondly,the change rule of smoke back-layering length of the double fires under longitudinal ventilation tunnel is revealed through experiments and theoretical analysis.It is found that under the same heat release rate and longitudinal velocity,the smoke backlayering length shorten obviously with the increase of the distance between double fires.Finally,The smoke back-layering length model and the maximum temperature model of double fires under longitudinal velocity are established.Finally,the study on the central minimum temperature and the maximum temperature rise of double fires under the roof was carried out.It is found that with the increase of the ceiling extraction velocity,the temperature in the tunnel decreases obviously,and the decrease trend of the temperature near the smoke outlet is more clear.And the temperature fall with the increase of the distance between double fires,and the lowest temperature occurs below the vent.The reason why maximum temperature decreases is that the increase of the ceiling extraction rate and the distance between double fires,and the maximum temperature increases obviously mainly because the enhance of the heat release rate.Finally,the prediction models of the central minimum and the maximum temperatures of the double fires are established.