Studies On The Effect Of Lateral Mechanical Smoke Exhaust In Underground Buildings

The application development of underground buildings has received more and more attention due to the increase of urban population and the increasing tension of ground land resources.However,serious accidents and property losses will occur in the event of a fire accident because of its semi-closed,poor ventilation and fewer escape routes.Studies have shown that most of the casualties are caused by high temperature toxic fumes,so it is very important to exhaust smoke quickly and effectively.The lateral mechanical exhaust system not only has the characteristics of small influence by external conditions and strong adaptability,but also can weaken or even prevent the occurrence of plug-holing and effectively improve the efficiency of exhausting smoke.By studying the factors affecting the lateral mechanical smoke exhausting effect,it has guiding significance for the optimization design of the lateral mechanical smoke control system of underground buildings in the future.A full-scale test bench was used to study the effect of smoke exhaust rate,smoke vent height and smoke vent length-width ratio on lateral mechanical smoke exhaust in underground building fires.The lateral mechanical exhaust system can quickly and effectively emit smoke and control the temperature of indoor smoke.Smoke exhaustion gradually increases with the increase of smoke exhaust rate and the height of the exhausting outlet,conversely,decreases with the increase of the aspect ratio of the exhaust outlet.The lateral mechanical exhaust system has an overall improved exhaust efficiency compared to conventional vertical mechanical exhaust.According to the relationship between the height of the dimensionless exhaust port and the effective exhaust amount,when the lateral exhaust port is at a height of 1/4 of the ceiling Basically,the best smoke exhaustion effect can be achieved.The plug-holing phenomenon of lateral mechanical exhaust occurs in the lower right corner of the exhaust vent.The results show that there is a critical exhaust rate when the height of the lateral exhaust is constant,and the plug-holing phenomenon occurs when the exhaust rate is greater than the critical rate.As the rate of smoke is further increased,the area of the plug-holing will become larger and the thickness ofplug-holing will increase.A reduction in the position of the exhaust vent will promote the early occurrence of the plug-holing phenomenon.As the aspect ratio of the exhaust vent increases,the plug-holing area is getting deeper and deeper and closer to the exhaust vent.The thickness of the smoke layer measured by the N-percent method is basically the same as the thickness of the smoke layer measured by the experiment,and the judgment of the phenomenon of the plug-holing is basically the same.According to the plug-holing phenomenon in the experiment and the Froude number under various working conditions,the critical suction Froude number of the lateral mechanical exhaust is 0.95.