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

Combined Buoyancy- and Pressure-Driven Flow Through a
Shallow, Horizontal Circular Vent.
(752 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.
*