Study On The Influence Of The Length And Wind Speed Of Fire Zone Of The Utility Tunnel On Fire And Smoke Exhaust Characteristics

The utility tunnel also known as the common ditch,is built under the urban road to take in the tunnel space for all kinds of pipelines,which is convenient for the unified management of urban pipelines and greatly improves the utilization rate of underground space.In the process of the city’s future development,the utility tunnel plays an increasingly important role in optimizing the city’s appearance and improving the city’s quality,but its cost is relatively expensive.However,in recent years,the occurrence of fire in the utility tunnel is common,while the occurrence of safety accidents also caused huge economic losses,so we should not only consider its safety problems,but also to reduce the construction cost as much as possible.In this paper,Pyrosim software was used to study the effects of smoke exhaust wind speed and fire partition length on smoke exhaust characteristics in cable cabin after fire.Firstly,the whole process of flue gas flow when fire occurs in the cable cabin is analyzed.Then select the wind speed in accordance with the standard,and from the smoke exhaust time and energy consumption two aspects of comprehensive consideration,the best smoke exhaust wind speed;Finally,the method of multi-objective optimization is used to determine the appropriate fire partition length by taking the maximum smoke concentration at the characteristic height of the human body in the time required for the maintenance personnel to escape to the safety zone is taken,the smoke exhaust time after the fire is extinguished,and the minimum energy consumption per unit length when the smoke is discharged as the target factors.Under the existing research conditions,24 research conditions were established,among which the smoke exhaust wind speed was selected: 2m/s,3m/s,4m/s,and the fire partition length was selected from 100 m to 450 m,8 different lengths.Finally,it can be seen that: after a fire occurs in the cable cabin,the smoke spreads from the fire source along the top to both ends and finally fills the whole cabin.In addition,when the smoke is discharged,the velocity stratification phenomenon will occur,and the smoke in the lower layer will be discharged first.In the early stage of smoke extraction,the concentration of the flue gas measured near the smoke outlet increases slightly.After a period of time,the concentration of the flue gas begins to decrease rapidly,until the flue gas is completely discharged.Under the premise that the length of the fire partition is a fixed value,the energy consumption is the lowest when the smoke exhaust wind speed is 4m/s,which is the same for all lengths.However,the energy consumption per unit length is different for different fire partition lengths,and the energy consumption per unit length is the lowest for 450 m.During the period from the occurrence of the fire to the time when the maintenance personnel fled to the safe area,the maximum smoke concentration at the characteristic height of the human body in the cable cabin first decreased and then increased with the increase of the length of the fire partition,and the smoke exhaust time increased with the increase of the length of the fire partition.When the fire partition length is 300 m,its comprehensive performance is the best,and the comprehensive performance of 250 m is lower than that of 300 m and 100 m.Combined with the actual project,the fire partition length is more appropriate between 200 m and 300 m.