Density jumps in smoke flow along horizontal ceilings

The entrainment of ambient air by the formation of density jumps in horizontal smoke flows below a ceiling is analyzed with the help of the classical graphical method for analyzing hydraulic jumps. The analysis shows that although the formation and intensity of such jumps are determined by the nature of the upstream flow, which may be characterized by the upstream Froude number, the value of the entrainment in a density jump cannot be determined without specifying some of the downstream boundary conditions. However, we show that a maximum entrainment value exists for each upstream Froude number and an explicit equation for its value is derived. This equation, which may be used for design purposes, shows that entrainment due to density jumps can double and even triple the horizontal smoke mass flux. (C) 2004 Elsevier Ltd. All rights reserved.