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TECHNICAL PAPERS: Natural and Mixed Convection

Three-Dimensional Mixed Convection in Plane Symmetric-Sudden Expansion: Bifurcated Flow Regime

[+] Author and Article Information
M. Thiruvengadam, B. F. Armaly, J. A. Drallmeier

Department of Mechanical and Aerospace Engineering, University of Missouri—Rolla, Rolla, MO 65401

J. Heat Transfer 129(7), 819-826 (Jul 25, 2006) (8 pages) doi:10.1115/1.2712850 History: Received January 27, 2006; Revised July 25, 2006

Simulations of three-dimensional laminar mixed convection in a vertical duct with plane symmetric sudden expansion are presented to illustrate the effects of the buoyancy-assisting force and the duct’s aspect ratio on flow bifurcation and heat transfer. The stable laminar bifurcated flow regime that develops in this geometry at low buoyancy levels leads to nonsymmetric temperature and heat transfer distributions in the transverse direction, but symmetric distributions with respect to the center width of the duct in the spanwise direction. As the buoyancy force increases, due to increases in wall heat flux, flow bifurcation diminishes and both the flow and the thermal fields become symmetric at a critical wall heat flux. The size of the primary recirculation flow region adjacent to the sudden expansion increases on one of the stepped walls and decreases on the other stepped wall as the wall heat flux increases. The maximum Nusselt number that develops on one of the stepped walls in the bifurcated flow regime is significantly larger than the one that develops on the other stepped wall. The critical wall heat flux increases as the duct’s aspect ratio increases for fixed Reynolds number. The maximum Nusselt number that develops in the bifurcated flow regime increases as the duct’s aspect ratio increases for fixed wall heat flux and Reynolds number.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the computational domain

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Figure 2

Comparison to measured results of Fearn (4) (solid lines represent simulated values)

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Figure 3

Streamlines in the bifurcated and nonbifurcated flow regimes (AR=4)

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Figure 4

Effects of wall heat flux on the xu lines (∎ locations of the jetlike flow impingement)

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Figure 5

Effects of wall heat flux on the streamwise distributions of the Nusselt number

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Figure 6

Effects of wall heat flux on the spanwise distributions of the Nusselt number

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Figure 7

Effects of wall heat flux on the streamwise distributions of the friction coefficient

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Figure 8

Bifurcation diagram for AR=8

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Figure 9

Effects of duct’s aspect ratio on xu lines (∎ locations of the jetlike flow impingement)

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Figure 10

Effects of duct’s aspect ratio on the streamwise distributions of the Nusselt number

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Figure 11

Effects of duct’s aspect ratio on the spanwise distributions of the Nusselt number

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Figure 12

Effects of duct’s aspect ratio on the streamwise distributions of the friction coefficient

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