Theoretical And Experimental Study On Flame Radiation Near Fire Source In Tunnel

With the rapid development of highway tunnels,tunnel fires occur frequently.Fires not only cause significant casualties,but also have an important impact on the safety of tunnel structure.Based on the design parameters of a highway tunnel and the F_r similarity criterion,a1/20 reduced scale model tunnel was built.Two kinds of burners were chosen as fire source and liquefied petroleum gas(LPG)was used as fuel.Under different combined conditions of longitudinal wind speed and gas flow rate,the radiation heat flux on the tunnel floor was measured and the flame video was taken simultaneously.According to the flame images obtained from the experiments,the visible flame shape was described by back-to-back frustums of a cone.Firstly,the geometric parameters were calculated and its variations with the momentum flux ratio were given out.Secondly,based on the visible flame shape model,a series of closed-form expressions to calculate the geometric view factor of arbitrary location on tunnel floor were given out.And the geometric view factor under the model were compared with those of cylinder model.Thirdly,combining the geometric view factor with the measured radiation heat flux,the radiation heat flux at some measuring points were predicted,and compared with the measured radiation heat flux.The measured and predicted values are in good agreement,which verifies the accuracy of the flame shape model.Fourthly,considering the coupling effect of transverse air supply and gas jet velocity,four typical cases are selected to further estimate the thermal radiation field of the tunnel floor near the fire source area in the prototype tunnel,which can determine the gradient of radiation heat flux distribution in the tunnel floor.Lastly,the radiation fraction of the two groups of experiments was solved based on the double-circular-table model,and the relationship between the radiation fraction and the momentum ratio was obtained.At the same time,the correlation between(?) was obtained and compared with the previous data.Finally,the research direction and content of the follow-up work are briefly discussed.