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Research Papers

Buoyancy-Driven Flow in Two Interconnected Rooms: Effects of the Exterior Vent Location and Size

[+] Author and Article Information
R. Tovar, C. A. Campo Garrido

Centro de Investigación en Energía, Universidad Nacional Autónoma de México, Privada Xochicalco s/n, Colonia Centro, Temixco, Morelos 62580, México

P. F. Linden

Department of Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 920903-0411

L. P. Thomas

Instituto de Física Arroyo Seco, Universidad Nacional del Centro, Pinto 399, 7000 Tandil, Argentina

J. Sol. Energy Eng 131(2), 021005 (Mar 24, 2009) (6 pages) doi:10.1115/1.3097272 History: Received April 10, 2007; Revised October 10, 2008; Published March 24, 2009

This paper describes scale-model laboratory experiments with salt-bath simulations, on the flow and stratification in two coupled rooms connected to the exterior by a single vent. The two rooms are connected by two openings one at high-level and one at low-level in the dividing wall. One “forced” room has a buoyancy source, while the outlet vent is in the “unforced” room and is placed in such a way that the buoyancy in the room can potentially drive an exchange flow through it. The buoyancy source is also a source of volume flux, such as cool air pumped into a room from an overhead duct, in which case the outlet is on the floor of the unforced room. We consider the effect of the size of the outlet vent on the resulting stratification in the two rooms. For a small vent only unidirectional flow occurs, and since no ambient fluid enters the rooms, the buoyancy in both rooms becomes uniform and approaches asymptotically to the buoyancy of the source. Above a critical vent size a bidirectional flow is driven through the vent by the buoyancy forces. In this case ambient fluid enters the rooms and a steady state is reached when the buoyancy flux through the outlet vent equals that of the buoyancy source. Both rooms remain stratified with two-layer weak stratification in this case, with a mean density that decreases as the size of the outlet increases. The implications for ventilation are discussed.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental setup. All units are in centimeters.

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Figure 2

Enhanced shadowgraph of the flow at t∼600 s for the intermediate outlet vent. The three main—turbulent—flows indicated in the photograph are (a) forced plume, (b) returning flow, and (c) and (d) exchange flow. The high-level interior opening is not visible as the lid of the tank obstructs the view.

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Figure 3

Flow schematic of the experiments. (a) The smallest outlet vent has unidirectional flow to the exterior. (b) The intermediate outlet vent has an exchange flow allowing ambient fluid to enter the tank.

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Figure 4

Density profiles in the forced and unforced rooms for the three different exterior opening sizes. Stars represent the direct measurements of samples taken from the model.

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Figure 5

Comparison of the theoretical model and the experimental results for the three opening sizes. Lines represent theoretical solutions, symbols represent experimental volume-averaged densities obtained with the dye technique, and stars represent the mixed-fluid final density obtained with the density meter.

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