Experimental Study On Influence Of Longitudinal Ventilation Mode On Smoke Movement Characteristics In Tunnel

With the rapid development of China’s economic construction,various railway tunnels.So far,China has become the country with the largest number of tunnels and the longest total length of tunnels in the world.However,more frequent tunnel fires and more prominent smoke control problems will follow.Longitudinal ventilation is often used in tunnel smoke control strategy.In this paper,the longitudinal ventilation is divided into positive pressure ventilation and negative pressure ventilation according to the positive and negative values of the pressure before and after the fire source under jet fan ventilation,and full section ventilation and partial section ventilation according to whether the section is closed to the outside.In this paper,a series of fire tests were carried out in a 1/20 scale tunnel with propane flow rate of 0.12 m~3/H～1.19 m~3/h,corresponding to the theoretical value of heat release rate(HRR)of 2.8 k W～28 k W and full-scale 5 MW～50 MW.The critical velocity,smoke backlaying,temperature distribution and fire heat release rate of different ventilation modes were studied in horizontal and inclined tunnels.This paper analyzes the differences between the critical velocity,heat release rate and pressure of different ventilation modes,he results show that the efficiency of negative pressure ventilation is 10.2%higher than that of positive pressure in horizontal tunnel,and15%～22%higher than that of positive pressure in Slope Tunnel.At the same time,this paper studies the ventilation efficiency and slope factor of different ventilation modes in inclined tunnel,analyzes the influence of slope on ventilation efficiency,and puts forward that the slope factor of negative pressure ventilation is a specific constant k_g=1.27,It is not proportional to slope in positive pressure ventilation:=1-0.031.Last,this paper focuses on the differences of vertical temperature distribution between horizontal tunnel and inclined tunnel,jet positive pressure and negative pressure,full cross-section ventilation and partial cross-section ventilation,and the highest temperature under the ceiling,and compares with the previous formula model,through the formula parameters to reflect the temperature distribution characteristics of different ventilation methods.The conclusion of this paper provides a theoretical basis for the specific selection of longitudinal ventilation mode in tunnel,and provides a new idea for the study of critical velocity in inclined tunnel,which has a certain guiding significance for tunnel fire smoke control.