Analysis Of Temperature Field Distribution And Smoke Flow Characteristics Of Cable Fire In Underground Pipe Gallery

With the rapid development of China's economy,Underground Comprehensive pipe gallery has become one of the important urban infrastructures of the national "13th Five-Year Plan".One of the essential problems to pipe gallery is fire.Due to ventilation restrictions,once it catches fire,a great quantity of hot smoke will be difficult to be exhausted promptly,which may cause a sharp rise in the temperature inside the corridor.In this case,the power and communication cable in the corridor can be quickly ignited,making serious consequences,like economic damage even the whole city may go collapse.It is very common to find that tunnel fire caused by cable fire.Based on the test of YZ-type rubber cables' combustion characteristics,we analyze the combustion characteristics of the rubber sheath,including oxygen index and pyrolysis characteristics under external heat flow.The heat value of YZ cable rubber sheathed material is 11308.5 kJ/kg.In the case of tightly ranking and intermittently ranking,the critical radiant heat flow is 24.75 kW / m2 and 27.40 kW / m2.Through the experimental study of small-scale fire model,it is found that the pipe gallery fire burns more intensely during 200s-600 s,which accounts for only 23% of the burning time,but contributes 75% of the mass loss.According to the mass loss rate,the average heat release rates in the small scale model experiments are 34.19 kW,24.06 kW,17.19 kW,for the fire source of 1 #,2 # and 3 #.According to the similarity principle,the average heat release rate of 1 #,2 # and 3 # fire source in the full-size fire test is 533.02 kW,375.09 kW and 279.06 kW.Based on the model experiment and theoretical analysis,it is found that the maximum temperature rise below the ceiling only relates to dimensionless heat release rate and distance between the fire source and the ceiling.It also finds that the ceiling temperature attenuated in the longitudinal direction exponentially.The experimental data finds to be reasonable so we propose the maximum temperature rise model below the ceiling.Through the combination of model experiment and theoretical study;it is found that the ceiling temperature attenuates exponentially in the longitudinal direction.Based on the experimental data,we propose the longitudinal temperature distribution model of the ceiling.The results show that the maximum temperature and longitudinal temperature distribution of the ceiling are consistent between the numerical simulation results of small size model and the experimental data,verifying the feasibility of FDS numerical simulation software in the study of pipe gallery fire.Through a large number of numerical simulations,combined with theoretical analysis,it is found that dimensionless flue gas upstream length only relates to dimensionless fire source power and dimensionless wind speed.Based on the dimensionless analysis of the simulated data,we hereby propose a prediction model of the flue gas upstream length of the pipe gallery.According to the previous research theory and the empirical formula,it is found that the dimensionless longitudinal critical wind speed only relates to the dimensionless fire source power.After dimensionless analysis,we propose a dimensionless critical wind speed prediction model.