Research On The Critical Velocity Of Fire Smoke Back-flow In Mine Horizontal Roadway

The mine fire smoke is easy to back flow to the upwind caused by the thermal buoyancy effect,then results in the flue gas spreading disorderly and increasing the difficulty to control it.That impedes the emergency evacuation and prevents the firemen from closing to the fire and fighting it through the ventilation direction.This paper is to study the distribution law of flue gas under there typical laneway structure based on the real mine tunnel.The formula is proposed to predict the critical velocity(or ventilation quantity)to stop the smoke from back flow to the upwind,making recommendations to help staff evacuation and protect the mineral resource.Combined with horizontal straight laneway critical velocity formula,the critical velocity which considered the blockage rate is put forward.The laneway fire under different blockage rates and fire resource places is simulated by using the FDS which is verified to be accurate.The formula calculation results are compared with the simulation results,and conducted the correlation validation,the simulation results are well consistent with the formula predict values shows the reliability of the formula.The change rules of the critical velocity are mastered.When the blockage rate changes from 0% to 10.56%,the critical velocity decreases from 2.895m/s to 2.616m/s.The critical velocity will not be affected by the obstruction when the fire place is keep away from the obstruction over 4.5 meters at the blockage rate of 10.56%.The wind speed distribution law at the bifurcation laneway fork is analyzed based on the conservation equations.The horizontal bifurcation laneway fire when one tunnel is on fire is simulated and the distribution formula is verified combined with the FDS simulation model.The smoke spreading regulation and the critical velocity that prevent the flue gas from invasion to the branch tunnel are acquired.It decreases as the laneway ventilation speed increases,and increases when the heat release rate increases.When the ventilation speed increases from 0 m/s to 3 m/s,the branch roadway critical velocity increases from 3.26 m/s to 2.38 m/s at the heat release rate of 5MW.Based on the research about the critical velocity formula at horizontal laneway,the critical ventilation quantity formula at the solo ended laneway is put forward and the numerical calculation model is set to simulate the fire.Comparing the simulation results and the formula calculation results,and using the correlation coefficient methodto verify the formula shows the applicability of it.The critical ventilation quantity increases as the heat release rate increases.And while the distance between the fire source and the vent position first decreases then increases,the critical ventilation quantity first increases then decreases finally tends to be stable.When the air duct diameter increases from 0.4 meter to 0.6 meter,the critical velocity decreases from 20m/s to 7.88 m/s,which implies that the duct size has a great influence on the resistant friction.It can magnify the duct size if the laneway structure were allowed to reduce the resistance loss,meanwhile to improve the efficiency of the laneway ventilation and to decline the critical velocity.