Vent Flows in Fire Compartments with Large Openings
The Kawagoe vent flow model has been widely used to study fully developed compartment fires. It is well known that the Kawagoe model is only adequate for compartments with relatively small openings because it overestimates the vent flow rates for compartments with large openings. For a compartment with a very wide opening occupying a large fraction of one wall, experimental observations show that a uniformly distributed fuel load within could produce a line fire parallel to the opening, slowly progressing into the compartment. In this article, analytical analysis has been performed to study the vent flow due to a line plume fire within the compartment, with comparisons to the Kawagoe vent flow model. The analysis shows that for large openings, the vent flow is dictated by the plume entrainment, and as the size of the opening is reduced, the flow across the opening becomes restricted by the opening geometry, approaching the flow rate predicted by the Kawagoe model. Based on the line plume entrainment model, the analysis shows that for an opening occupying one entire wall, the line plume induced flow rate could be as low as 60% of the rate predicted by the Kawagoe model. The limiting vent opening geometry for applying the Kawagoe model is suggested. Simple approximate vent flow equations for large and small openings are also presented.