Experimental investigation on influence of smoke venting velocity and vent height on mechanical smoke exhaust efficiency

Abstract

Abstract:A set of burning experiments were conducted to investigate the influence of smoke vent height and exhausting velocity on mechanical smoke exhausting efficiency.Results have shown that the smoke exhausting process becomes more efficient due to the increased smoke vent height and the decreased exhausting velocity, which eliminate the plug-holing issue with fewer disturbances on the smoke layer interface.For each certain exhausting velocity, there is a critical value of distance between the vent and the bottom of the smoke layer. When the distance is less than the critical value, the smoke exhausting is inefficient, and the efficiency decreases sharply as the distance decreases. Contrarily, when the distance is greater than the critical value, a good efficiency can be acquired and the exhausted smoke increased relatively slowly as the distance increases. A critical Froude number, proposed by Hinkley to predict the onset of plug-holing effect in gravity venting systems, was validated in the experiments. However, the experimental results indicate that in the tests without the plug-holing, the fresh air entrained due to smoke exhausting is up to 48% of the mechanical exhausting rate.

A study of the effect of plug-holing and boundary layer separation on natural ventilation with vertical shaft in urban road tunnel fires

“…Vauquelin et al [22] also noticed the plug-holing in some of the transverse smoke exhausting experiments in a small scale tunnel with less net height and concluded that in the cases with plug-holing, the smoke exhausting efficiency had strongly decreased. Ji et al [23] experimentally studied the influence of smoke vent height and exhausting velocity on mechanical smoke exhausting efficiency, and concluded that in the tests without plug-holing, the fresh air entrained due to smoke exhausting is up to 30% of the mechanical exhausting rate, and in order to achieve an excellent smoke exhausting, the amount of fresh air entrained due to smoke exhausting should be considered and reduced to minimum. However, in these former studies, delicate quantitative analyses on plug-holing induced by vertical shaft have rarely been addressed.…”

“…However, if the shaft is so high that stack effect is strong enough to cause the occurrence of plug-holing, the lower fresh air will be directly exhausted and then the vertical shaft exhausts a mixture of smoky gases and clean air. Ji et al [23] experimentally studied the influence of smoke vent height and exhausting velocity on mechanical smoke exhausting efficiency, and concluded that once plug-holing occurs (with large exhausting velocity) due to the large amount of fresh air exhausted into the duct, less than half of the exhausting rate was smoke in the worst case. In addition, when plug-holing occurs, the disturbance on smoke-air interface enhances significantly (see Fig.…”

Maximum Smoke Temperature in Non-Smoke Model Evacuation Region for Semi-Transverse Tunnel Fire

“…High-temperature smoke generated by tunnel fire hazard destroys the tunnel structure and its toxic components threaten personnel security greatly (Jie et al 2010). Related researches reported that 85% casualties in tunnel fire hazard are caused by high-temperature toxic smoke.…”

Study of Numerical Analysis on Smoke Exhaust Performance of Portable Smoke Exhaust Fan

“…Meanwhile, a research on the smoke exhaust systems for the smoke emission in the event of a fire in the building has been underway. In particular, an impact of the exhaust speed and the height of exhaust opening in a mechanical smoke exhaust system on the smoke exhaust performance has been investigated [6] [7] [8].…”