A multi-scale experiment analysis of air entrainment and heat exhaust coefficient under lateral smoke exhaust in tunnel fires

Abstract

This study investigated the air entrainment caused by a lateral smoke exhaust system via full-scale and model-scale tests. A particular phenomenon, shear flow, was observed downstream of the exhaust vent. The phenomenon of shear flow was more intense when the exhaust velocity increased, which destroyed the smoke layer stratification and strengthened the air entrainment. Plug-holing and shear flow intensified air entrainment, and the functional relationship between air entrainment, Froude number, and dimensionless exhaust vent size was established. The relationship between the air entrainment and heat exhaust efficiency was studied, and it was found that the heat exhaust coefficient was positively related to the air entrainment. The functional relationship between the heat exhaust coefficient and air entrainment for different lateral exhaust vent sizes was presented. In addition, we observed that lateral smoke exhaust exhibit little effect on the centerline temperature distribution. A model that can be used to describe the centerline temperature distribution with lateral smoke exhaust systems was developed.