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Combined Buoyancy- and Pressure-Driven Flow Through a Shallow, Horizontal Circular Vent.


pdf icon Combined Buoyancy- and Pressure-Driven Flow Through a Shallow, Horizontal Circular Vent. (135 K)
Cooper, L. Y.

American Society of Mechanical Engineers. Heat Transfer With Combined Modes. ASME International Mechanical Engineering Congress and Exposition. HTD-Vol. 229. November 6-11, 1994, Chicago, IL, Beasley, D. E.; Cole, K. D., Editor(s)(s), 1-12 pp, 1994.

Journal of Heat Transfer, Vol. 117, 659-667, August 1995.

Keywords:

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

Abstract:

Combined buoyancy- and pressure-driven (i.e., forced) flow through a horizontal vent is considered where the vent-connected spaces are filled with fluids of different density in an unstable configuration (density of the top is larger than that of the bottom). With zero-to-moderate cross-vent pressure difference the instability leads to a bi-directional exchange flow between the two spaces. For relatively large the flow through the vent is un-idirectional, from the high- to the low-pressure space. An anomaly of a standard vent flow model, which uses Bernoulli's equation with a constant flow coefficient is discussed. Thus, the standard model does not predict expected bi-directional flows at small-to-moderate or non-zero flows at [equation]. Also, when [equation] exceeds the critical value [equation], which defines the onset of uni-directional or "flooding" flow, there is a significant dependence of [equation] on the relative buoyancy of the upper and lower fluids (i.e., [equation] is not constant). Finally, the location of the high-pressure side of the vent, i.e., top or bottom, can be expected to influence vent flow characteristics. Analysis of the relevant boundary value problems and of available experimental data lead to a general mathematical model of the vent flow which removes the anomaly of the standard model and which takes all the above effects into account. The result is a algorithm to calculate flow through shallow, horizontal, circular vents under high-Grashof number conditions.