Visualization of Transport Across a Horizontal Vent Due to Density and Pressure Differences.
Visualization of Transport Across a Horizontal Vent Due
to Density and Pressure Differences.
Jaluria, Y.; Lee, S. H. K.; Mercier, G. P.; Tan, Q.
American Society of Mechanical Engineers (ASME).
National Heat Transfer Conference. Visualization of
Heat Transfer Processes. HTD-Vol. 252. August 1993,
Atlanta, GA, Am. Soc. of Mechanical Engineers, New York,
NY, 1-17 pp, 1993.
Sponsor:National Institute of Standards and Technology,
vents; water flow; air flow; flow visualization;
A very important flow and transport circumstance that
arises in practical problems such as enclosure fires is
that of heat and mass transfer across a horizontal vent.
Such vents exist in enclosed regions such as rooms and
energy storage and ventilation systems. It is important
to understand the basic nature of the transport
processes that arise because of finite, non-zero,
density and pressure differences that usually exist
across such vents. The flow is driven by these two
mechanisms and very complicated flow patterns arise,
depending on the governing variables in the problem.
For instance, a dominant pressure effect results in a
unidirectional flow, whereas significant buoyancy
effects lead to a bidirectional flow exchange. The heat
and mass transfer associated with the flow is similarly
strongly influenced by the flow regime. There is a
strong need for visualization to determine if a
unidirectional or a bidirectional flow exists across the
vent and to study the basic characteristics of the
transport processes involved. This paper presents a
study of this heat and mass transfer problem employing
water and air as the fluid media for two different
experimental systems. Pure and saline water are used in
the first case to obtain the unstably stratified
circumstance with a pressure difference across the vent.
Air at different temperature levels is used in the
second case. A laser sheet, with smoke, is used for
visualization in air and a shadowgraph for water. Other
visualization techniques are also used to obtain
qualitative and quantitative results on the flow
direction, transport rates and the relevant mechanisms.
Since transient effects are important in many cases,
video recordings are employed to obtain the frequency of
observed oscillations in the transport and for
determining the transition from one regime to the other.
Visualization is crucial to the understanding of these
processes and to the determination of the transport
regime under various operating conditions.