Effect Of Obstacles In Slender Rectangular Containers On Hydrogen Vented Explosion Characteristics

Hydrogen energy,a renewable clean energy in the future,has been highly studied at home and abroad.Hydrogen is considered to be one of the most dangerous gases because of its wide combustion range,low ignition energy and fast combustion rate.Once hydrogen occur accidental explosion,it will pose a major threat to life and property.Vented explosion technology is one of the effective means to protect property and life from threats.In this paper,the effects of hydrogen concentration,vent area,blockage ratio and combined effects with obstacles on the vented explosion characteristics of hydrogen/air premixed gases are investigated experimentally.Firstly,the flame image captured by schlieren technology and further to study the flame propagation characteristics.Then,the pressure dynamic characteristics are studied through the pressure curve collected by the pressure sensor.Combining with the flame images,it is found that the flame evolution process in the container in the case of obstacle-free undergoes four flame forms,namely finger-shaped flame surface,plane flame surface,Tulip flame surface and Distorted-Tulip flame surface.In terms of finger-shaped flame front,the wrinkled flame front is mainly attributed to the combined effect of thermal diffusion instability and molecular diffusion instability.After Tulip flame,the wrinkling of flame front is mainly attributed to the evolution of Distorted-Tulip flame.In the case of the obstacle,the flame develops forward in the form of convex upward and concave downward due to the influence of the induced reflection wave of obstacles on the flame surface.After the flame passes through the obstacle,the turbulence of combustible gas induced by the obstacle leads to the formation of flame instability.In the range of lean hydrogen concentration,the flame propagation velocity increases with the increase of hydrogen concentration.On the contrary,in the case of obstacle,the flame propagation speed increases over time at the same hydrogen concentration.At the same time,according to the experimental results,it is also found that the flame propagation speed is greatly affected by the blockage ratio,which is mainly attributed to the combined effect of the different turbulence intensity of the unburned gas and the changing flame area.The pressure collected by piezoelectric pressure transducer shows that there are two pressure peaks in the container in the case of the obstacle-free.The formation of a pressure peak P1 is mainly influenced by the venting plate.This is attributed to the fact that there is only a single productivity behavior in the vessel before breaking the venting plate,resulting in an increase in pressure.After breaking the venting plate,the pressure begins to decrease due to the emission effect.The formation of another pressure peak P2 is mainly attributed to the acoustic-structure.In the range of the lean hydrogen concentration,the pressure peak P1 increases monotonously with the increase of hydrogen concentration,and the corresponding pressure rise rate increases correspondingly.However,the change of hydrogen concentration has little effect on the pressure peak P2.Meanwhile,the influence of the vent area on the overpressure inside the container cannot be ignored.With the increase of the vent area,the maximum pressure inside the vessel begins to decrease,and the maximum pressure inside the vessel can even be reduced by more than 90% when the vent area reaches a certain critical value.Therefore,the parameter design of the vent area is very important to the vented explosion technology.In the case of obstacles,three pressure peaks are found in the container.It is noteworthy that the third pressure peak P3 is mainly induced by obstacles.The reason is that the obstacle induces the turbulence of the unburned gas and the increased flame area,which leads to the instantaneous acceleration of the combustion speed of the unburned gas,and further results in the larger rate of volume production by combustion than the discharged rate through the vent.The pressure inside the container rises again,finally forming the pressure peak P3.The vented explosion overpressure is deeply affected by the blockage ratio.The pressure peak P3 first increases with the increase of the blockage ratio,and then decreases with the further increase of obstruction ratio.However,the blockage ratio has little effect on the pressure peaks P1 and P2.The combined effect of obstacle and hydrogen concentration on pressure peak P3 was significantly higher than that on pressure peak P1.The number of pressure peaks is affected by the combined effect of vent area and obstacles.When the vent area is reduced to the critical value,the pressure peak P1 and the pressure peak P3 are coupled to form a larger pressure peak P,which results in two pressure peaks in the vessel.