The plug-holing of lateral mechanical exhaust in subway station: Phenomena, analysis, and numerical verification

Abstract

As one of the effective way of smoke exhausting method, the lateral mechanical exhaust system is gradually being adopted in more and more scenarios. While compared to the numerous investigations on the ceiling exhaust system, the of influence of plug-holing and the key factors that affect the smoke exhaust effect of lateral system are quite insufficient. During the smoke exhaust process, the plug-holing phenomenon will cause the fresh air to be drawn directly into the exhaust vent, and thus weakening the smoke exhaust effect. To reveal the key factors that influencing the smoke exhaust effect and the plug-holing phenomenon, a set of numerical simulations were conducted in a subway station with the lateral mechanical exhaust. Results show that with the increase of exhaust velocity, the phenomenon of plug-holing will occur at the lateral exhaust vent. The occurrence of plug-holing can lead to the decrease of the exhausted smoke concentration. Furthermore, by introducing a virtual smoke vent that perpendicular to the original lateral one, a critical Froude number for predicting the occurrence of plug-holing of lateral mechanical exhausting is proposed. Based on the results of different exhaust velocities, heat release rates and smoke vent heights, the critical Froude number that corresponds to the occurrence of the plug-holing can be determined as 0.5 for the lateral mechanical exhaust.