Research Papers

Bouyancy Effect on Forced Convection in Vertical Tubes at High Reynolds Numbers

[+] Author and Article Information
LiDong Huang

 Heat Transfer Research, Inc., 150 Venture Drive, College Station, TX 77845lh@htri.net

Kevin J. Farrell

 Heat Transfer Research, Inc., 150 Venture Drive, College Station, TX 77845

J. Thermal Sci. Eng. Appl 2(4), 041003 (Jan 19, 2011) (6 pages) doi:10.1115/1.4003280 History: Received October 06, 2010; Revised December 16, 2010; Published January 19, 2011; Online January 19, 2011

The complex interaction of forced and natural convections depends on flow regime and flow direction. Aiding flow occurs when both driving forces act in the same direction (heating upflow fluid and cooling downflow fluid), opposing flow occurs when they act in different directions (cooling upflow fluid and heating downflow fluid). To evaluate mixed convection methods, Heat Transfer Research, Inc. (HTRI) recently collected water and propylene glycol data in two vertical tubes of different tube diameters. The data cover wide ranges of Reynolds, Grashof, and Prandtl numbers and differing ratios of heated tube length to diameter in laminar, transition, and turbulent forced flow regimes. In this paper, we focus the buoyancy effect on forced convection of single-phase flows in vertical tubes with Reynolds numbers higher than 2000. Using HTRI data and experimental data in literature, we demonstrate that natural convection can greatly increase or decrease the convective heat transfer coefficient. In addition, we establish that natural convection should not be neglected if the Richardson number is higher than 0.01 or the mixed turbulent parameter Ra1/3/(Re0.8Pr0.4) is higher than 0.05 even in forced turbulent flow with Reynolds numbers greater than 10,000. High resolution Reynolds-averaged Navier–Stokes simulations of several experimental conditions confirm the importance of the buoyancy effect on the production of turbulence kinetic energy. We also determine that flow regime maps are required to predict the mixed convection heat transfer coefficient accurately.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Buoyancy effect on heat transfer for aiding and opposing flows (3)

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Figure 2

Schematic of mixed convection tests using MBU

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Figure 3

Laminarization of upflow heating data

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Figure 4

Experimental data showing natural convection effect for aiding flow

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Figure 5

HTRI upflow heating data showing natural convection effect

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Figure 6

(a) Temperature and (b) velocity profiles for vertical water flow

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Figure 7

(a) Temperature and (b) velocity profiles for vertical water flow



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