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Research Papers: Heat Transfer Enhancement

A Numerical Investigation of Turbulent Flow and Heat Transfer in Rectangular Channels With Elliptic Scale-Roughened Walls

[+] Author and Article Information
Feng Zhou

e-mail: zhoufeng@ucla.edu

Ivan Catton

e-mail: catton@ucla.edu
Department of Mechanical and Aerospace Engineering,
University of California,
48-121 Engineering IV,
420 Westwood Plaza,
Los Angeles, CA 90095

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received July 1, 2012; final manuscript received April 16, 2013; published online June 27, 2013. Assoc. Editor: James A. Liburdy.

J. Heat Transfer 135(8), 081901 (Jun 27, 2013) (9 pages) doi:10.1115/1.4024278 History: Received July 01, 2012; Revised April 16, 2013

In the present paper, rectangular channels with six types of elliptic scale-roughened walls for heat transfer enhancement are numerically studied. Heat transfer and fluid flow characteristics for sixteen different scale-roughened models (with the scale height varying in the range from 1 mm to 2.5 mm) are numerically predicted using commercial computational fluid dynamics (CFD) code, Ansys cfx. The turbulent model employed is the k–ω based shear–stress transport (SST) model with automatic wall function treatment. In the performance evaluation, we use a “universal” porous media length scale based on volume averaging theory (VAT) to define the Reynolds number, Nusselt number, and friction factor. It is found that heat transfer performance is most favorable when the elliptic scales are oriented with their long axis perpendicular to the flow direction, while the scales elongated in the flow direction have lower Nusselt numbers and pressure drops compared with the circular scale-roughened channels. Results indicate that the scale-shaped roughness strongly spins the flow in the spanwise direction, which disrupts the near-wall boundary layers continuously and enhances the bulk flow mixing. With the flow marching in a more intense spiral pattern, a 40% improvement of heat transfer enhancement over the circular scale-roughened channels is observed.

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Figures

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Fig. 1

Geometrical details of one of the elliptic scale-roughened surfaces

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Fig. 2

Print shapes of the elliptic scales

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Fig. 3

Computational domain. The length of the extended region was not drawn in scale.

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Fig. 4

Example of the grid system. Only part of the whole model is shown.

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Fig. 5

REV for a PFHS with scale-roughened surfaces

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Fig. 6

Validation of the present CFD simulation by comparing with experimental data by Chang et al. [14]

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Fig. 7

Nusselt number versus Reynolds number

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Fig. 8

Δp versus Reynolds number

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Fig. 9

Nusselt number versus scale height, ReDh = 10,000

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Fig. 10

Pressure drop versus scale height, ReDh = 10,000

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Fig. 11

Effectiveness factor versus Reynolds number

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Fig. 12

Streamlines on the planes normal to flow direction at Re = 10,000: (a) elliptic scale 2, Pt/Pl = 0.5; (b) circular scale, Pt/Pl = 1; and (c) elliptic scale 5, Pt/Pl = 2

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