Study On The Influence Of Sectional Shape And Wind Speed Of Utility Tunnel On Fire And Smoke Exhaust

The utility tunnel is a tunnel space built underground in the city.It can centrally distribute various municipal pipes in the tunnel for unified management,which can not only protect the pipeline but also improve the land utilization rate.However,with the construction of the utility tunnel and the increasing number of pipelines involved,various operational safety accidents have occurred.Among them,the risk of fire in cable cabins is the greatest,and how to effectively emit smoke after fire has always been the focus of attention.In this paper,the following aspects of the effects of the cable duct cross-section shape and wind speed on the smoke exhaust are studied by numerical simulation.Firstly,the cause of the fire in the cable cabin is analyzed,that is,the fire is caused by the cable itself and external factors.According to the characteristics of the fire and the flow of the smoke,suggestions are given on the ventilation system and fire protection construction.Secondly,according to the construction standard of the utility tunnel.,three different types of sections were designed,and the minimum ventilation and maximum ventilation during accident ventilation were determined according to the specifications,three standard wind speeds were selected,and nine working conditions were designed as comparisons.Finally,the fire dynamics simulation software PyroSim was used to establish the fire model,the nine kinds of working conditions were simulated and analyzed,the flow and temperature distribution of the flue gas in the combustion stage were observed,and the changes of the flue gas volume,wind speed and smoke density values under various working conditions in the exhaust stage were compared.Through the comparison and analysis of the simulation results,the following conclusions are drawn: In the combustion stage,the fire duration of the nine working conditions is less than 10 min under closed conditions,so it is feasible to use a closed self-extinguishing method to extinguish the fire;The temperature in the cable compartment is roughly parabolic,with a relatively high temperature section near the fire source,and a relatively low temperature away from the fire source.The maximum temperature value of the three types are different,type 1 has the largest aspect ratio,the highest temperature under the ceiling;The flow of flue gas in the cable cabin fire is the ceiling jet.The flue gas stays close to the ceiling during the flow and the thickness of the flue gas layer increases continuously,and the flow characteristics of the two ends are symmetric with the fire source as the center.During the exhausting stage,the order of smoke exhaust in the cable compartment is from bottom to top,and the lower layer of flue gas is discharged first,the efficiency of exhausting smoke under the ceiling is the lowest;When ventilating and exhausting,speed stratification occurs,and the lower layer speed is greater than the upper layer speed.Speed stratification is one of the main causes of smoke stratification when exhausting smoke;By comparing the exhaust efficiency of the nine working conditions,when the aspect ratio of the cable compartment is the same,as the ventilation speed is continuously reduced,the exhaust efficiency is also reduced.When the ventilation speed is the same,type 1 with the highest aspect ratio has the lowest efficiency,and the type 2 is the second.the type 3 with the lowest aspect ratio has the highest efficiency.