Study On Plugholing Phenomenon And Smoke Exhaust Efficiency In Centralized Extraction Tunnel

With the increasing expansion of cities and the increasing frequency of regional population flow,tunnels are playing a more and more important role as a media channel connecting people and goods exchange on both sides.Therefore,tunnel fire has attracted more and more attention.Centralized smoke exhaust,as a new smoke exhaust mode,has unique advantages over vertical smoke exhaust and horizontal smoke exhaust.Through model test,theoretical analysis and numerical simulation,this paper studies the suction air volume and optimal smoke exhaust efficiency of smoke layer in centralized smoke exhaust tunnel.It is hoped that through the study of suction and smoke exhaust efficiency,appropriate smoke exhaust air volume can be obtained for centralized smoke exhaust in tunnel.The main contents and research results of this paper are as follows:Through the small-scale tunnel model centralized smoke exhaust experiment,the phenomenon of smoke puncture under different exhaust air volume of single smoke outlet was studied.The smoke layer suction process under the tunnel centralized smoke exhaust outlet was studied experimentally.According to the law of conservation of mass,the absorption model of smoke puncture was studied.The critical Froude number of smoke puncture was calculated to be close to 1.8,and the smoke puncture process under the centralized smoke exhaust outlet of the tunnel was analyzed.The variation of temperature and thickness of square flue gas layer was studied.The variation trend of temperature and thickness of flue gas layer under single exhaust nozzle with the amount of exhaust air was studied.The non-suction zone,transition zone and complete suction zone were analyzed.The Froude number calculated under different exhaust air volume is very close to the actual situation,and the critical Froude number of small-scale and full-scale smoke puncture in a single exhaust is about 1.2 and 1.8,respectively.In order to analyze whether the numerical simulation can be used to study the phenomenon of smoke puncture in centralized exhaust,FDS was used to establish the same model as the small-scale experiment and set the same working conditions for simulation verification.Comparing a series of parameters,such as power of fire source,temperature of the measuring point below the exhaust port and thickness of the smoke layer,it is verified that the difference between numerical simulation data and experimental results is less than 10%.The numerical simulation can be used to study the phenomenon of concentrated smoke suction in tunnels very accurately.The temperature and velocity vectors of the smoke layer below the single exhaust port in tunnels are analyzed by the simulation slice visualization.Nowadays,because of the influence of one-dimensional spread velocity of smoke along the tunnel,the suction point of smoke exhaust outlet is not located in the center of the tunnel exhaust outlet,but deviates a certain distance from the one-dimensional spread direction.The air in the suction part is more supplied by the air in the one-dimensional spread direction than the air directly below the exhaust outlet.Full-scale numerical simulation was used to analyze the diffusion range of flue gas under the condition of different exhaust air volume,the distribution of temperature and CO concentration in different locations of the tunnel under different exhaust air volume,and the influence of temperature and CO transmission speed and distance on the exhaust air volume was analyzed.By calculating the quality of CO₂ and the quality of CO₂generation measured at the exhaust outlet,the exhaust efficiency of a single exhaust outlet and the overall exhaust efficiency are obtained.The energy efficiency ratio curve of the exhaust efficiency with the increase of the exhaust air volume is studied,and the most suitable exhaust air volume is obtained.Figure 31 table 7 reference 72...