Study On The Effect Of Side Venting On Methane Explosion Characteristics In A Duct

In recent years,gas explosion accidents occur from time to time,which causes a serious threat to industrial safety.To reduce the loss caused by gas explosion,this paper used the method of side venting to discharge methane explosion in a typical duct,and analyzed the influence of side venting on the characteristics of methane explosion in a duct with and without an obstacle.In this paper,a small-sized duct of 100×100×1000 mm~3 was designed and constructed independently,and side vents of different locations and areas were set up on the duct.Obstacles of different locations and blockage ratios could be set up in the duct according to different configurations.Two pressure sensors and a high-speed camera were used to collect pressure signals and flame propagation images of methane explosion in the duct,respectively,to analyze the influence of side venting on the characteristics of methane explosion in the duct.The Fluent numerical simulation method was used to simulate some typical configurations,to verify the experimental rules,and analyze the release mechanism of side venting on methane explosion.Firstly,the influence of locations and areas of side vents on the characteristics of methane explosion was studied in a duct without an obstacle.The results show that the side venting effect does not decrease monotonously with the increase of the distance between the side vent and the ignition point.The venting effect is affected by the side vent,the end vent and the interaction effect of each other.When the flame propagates in front and rear of the side vent,respectively,the side vent has the opposite effect on the flame propagation.The duration of high pressure stage of explosion overpressure is significantly correlated with the position of the side vent,which becomes longer with increasing the distance between the side vent and the ignition point.This is different from the relationship between the peak value of explosion overpressure and the side vent position.When the flame propagates in front of the side vent,the side vent not only just accelerates the flame,but also can decelerate the flame due to the release of partial fuel and explosion energy.The specific effect is related to the size of the vent area.At the same side vent position,with the increase of the area of the side vent,the peak value of explosion overpressure decreases obviously,and the discharge effect is better.Overpressure in the vicinity of the side venting position is less affected by the size of the side venting area,while the effect on overpressure at a far distance from the side venting position is relatively large.Secondly,the influences of the side venting position,venting area and the blockage ratio of the obstacle on the characteristics of methane explosion in a duct with an obstacle were studied.In a duct with an obstacle,the side vent could discharge the explosion efficiently,and the venting effect becomes weaker monotonously with the increase of the distance between the side vent and the ignition point.When the flame propagates before the side vent/obstacle,the influence of the side vent/obstacle on the flame propagation is very small.When the flame reaches the side vent/obstacle position,the flame begins to be significantly affected by the side vent/obstacle.Besides,the greater the explosion overpressure induced by the obstacle,the better the discharging effect of side vent on overpressure and the stronger the venting efficiency.When a side vent with small area is set in front of the obstacle,the obstacle will promote the flame to be released through the side vent,which is conducive to slow down the flame propagation.When the area of the side vent is large,the vent itself has a very strong discharging effect on the flame due to the large venting area.Therefore,the obstacle has little effect on discharging effect of the side vent on the flame.When the flame passes the obstacle,the obstacle always promotes the flame propagation.With the increase of blockage ratio of the obstacle,the acceleration effect on flame propagation increases gradually.Thirdly,based on the influence of the side vent on the characteristics of methane explosion in the duct with an obstacle,the effect of the relative position of the side vent and the obstacle on the characteristics of methane explosion was analyzed.When the side vent is set in front of the obstacle,before the flame is strongly encouraged by the obstacle,the flame has been discharged through the side vent,therefore,the overpressure can be effectively discharged and the flame propagation slows down rapidly.In this case,the discharging effect is less sensitive to the side venting area.When the flame passes the obstacle,the explosion intensity is low,and the encouragement of the obstacle on flame propagation is weak,which has little sensitivity to the blockage ratio.When the side vent is located behind the obstacle,the flame propagation velocity increases and the explosion intensity is enhanced rapidly due to the encouragement of the obstacle as the flame passes the obstacle.And the encouragement of the obstacle is very sensitive to the obstacle ratio.When the flame reaches the side vent,the flame has been strongly encouraged by the obstacle.The explosion intensity is great,and the flame transverse propagation velocity is high,which is not conducive for the side vent to discharge the explosion.In this case,the side venting effect is weak,and the venting effect is very sensitive to the side vent area.Finally,Fluent numerical simulation was used to simulate some typical configurations.The results shows that the Charlette model is effective in simulating the flame propagation process of methane explosion in a duct,which could reproduce the flame propagation process,flame structure and overpressure trend.The flow field trace and velocity vector directly shows that the main function time of the side vent is when the flame reaches the side venting position and later.When the flame propagates behind the side vent,the flow field behind the flame front in the duct is basically divided by the flame front.The flow field trace in the burned zone is toward the side vent,and the velocity near the side vent is larger.The flow field trace in the unburned zone ahead of the flame front is toward the end vent of the duct,but the velocity vector is small,and the power of flame propagation is weak.In the duct with an obstacle,with the increase of obstacle ratio,the boundary line of flow field track direction gradually moves from the flame front back to the burnt zone.