Flow of Smoke and Hot Gases Across Horizontal Vents in Room Fires

Abstract

An important circumstance that is often encountered in enclosure fires is that of heat and mass transfer across a horizontal vent. Such vents are present in enclosed regions such as rooms in multi-leveled buildings and in ships. The transport arises due to the finite density and pressure differences that usually exist across such vents. It is important to determine the resulting flow rate and the nature of the flow, particularly whether the flow is unidirectional and the direction in which it occurs or whether it is bidirectional across the vent, since the growth and spread of the fire are dependent on these characteristics. This paper presents a study of this heat and mass transfer problem, employing air at different temperature levels to provide the buoyancy. A laser sheet is used for visualizing the flow of smoke through the vent. Quantitative results are obtained on the resulting flow rates for wide ranges of the governing variables. It is also found that transient effects are important in most cases and temperature data are used to study the oscillations in the flow and to determine the transition from one regime to the other. Some correlations are derived from the measurements to characterize the dependence of the flow rate across the vent on the governing variables, such as pressure and temperature differences.