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Calculation of the Flow Through a Horizontal Ceiling/Floor Vent.


pdf icon Calculation of the Flow Through a Horizontal Ceiling/Floor Vent. (941 K)
Cooper, L. Y.

NISTIR 89-4052; 30 p. February 1989.

Sponsor:

Naval Research Lab., Washington, DC

Available from:

National Technical Information Service
Order number: PB89-189252

Keywords:

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.