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Combined Buoyancy- and Pressure-Driven Flow Through a Horizontal Vent: Theoretical Considerations.


pdf icon Combined Buoyancy- and Pressure-Driven Flow Through a Horizontal Vent: Theoretical Considerations. (720 K)
Cooper, L. Y.

NISTIR 5252; 17 p. September 1993.

Combustion Institute/Eastern States Section. Chemical and Physical Processes in Combustion. Technical Meeting, 1993. October 25-27, 1993, Princeton, NJ, 315-318 pp, 1993 AND Fire-and-Explosion Hazard of Substances and Venting of Deflagrations. 1st International Seminar Proceedings. July 17-21, 1995, Moscow, Russia, Molkov, V., Editor, 1-11 pp, 1995, 1993.

Available from:

National Technical Information Service
Order number: PB94-103694

Keywords:

vents; building fires; compartment fires; computer models; fire models; mathematical models; zone models

Abstract:

Flow through a horizontal vent is considered where the vent-connected spaces near the elevation of the vent are filled with fluids of different density in an unstable configuration, with the density of the top space larger than that of the bottom space. With zero-to-moderate cross-vent pressure difference the instability leads to a bi-directional exchange flow between the two spaces. For relatively large cross-vent pressure difference the flow through the vent is unidirectional, from the high- to the low-pressure space. For arbitrary specified cross-vent pressure difference, boundary value problems for the flow are formulated for cases where the fluid media in the two spaces are the same perfect gas, with relatively high and low temperature (corresponding to low and high density) in the lower and upper spaces, respectively. Two separate classes of problem are distinguished. In the first, the higher pressure is in the space above the vent. This enhances the downward component of the flow from the top to the bottom space, and diminishes, or reduces to zero, the upward flow. In the second, the higher pressure is in the lower space leading to enhancement of the upward flow, etc. Relationships between the two boundary value problems and their solutions are identified. These are useful for extending an available solution for one class of problem to that of the other and for unified understanding and correlation of experiment data for the two flow configurations.