vents; algorithms; building fires; compartment fires; computer models; computer programs; fire models; pressure differential; pressure effects; zone models; ceiling vents; oxygen concentration

Abstract:

Calculation of the flow through a horizontal vent located in a ceiling or floor of a multi-room compartment is considered. It is assumed that the environments of the two, vent-connected spaces near the elevation of the vent are of arbitrary relative buoyancy and cross-vent pressure difference. An anomaly of the standard vent flow model is discussed. The problem occurs in practical vent configurations of unstable hydrostatic equilibrium, where, for example, one gas overlays a relatively less-dense gas. In such configurations the cross-vent flow is not uni-directional. Previously published experimental data on a variety of related flow configurations are used to develop a general flow model which does not suffer from the standard model anomaly. The model developed leads to a uniformly valid algorithm, called VENTCL, for horizontal vent flow calcualtions suitable for general use in zone-type compartment fire models. Based on an assumption of total consumption of net oxygen flow rate, the algorithm is used in an example application where steady-state rate-of-burning in a ceiling-vented room is estimated as a function of room temperature, vent area, and oxygen concentration.

• buoyancy air flow