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RESEARCH PAPERS: Forced Convection

Mass (Heat) Transfer Downstream of Blockages With Round and Elongated Holes in a Rectangular Channel

[+] Author and Article Information
H. S. Ahn, S. W. Lee, D. Banerjee

Convective Heat and Mass Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123

S. C. Lau1

Convective Heat and Mass Transfer Laboratory, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123

1

Corresponding author.

J. Heat Transfer 129(12), 1676-1685 (Apr 29, 2007) (10 pages) doi:10.1115/1.2767748 History: Received June 23, 2006; Revised April 29, 2007

Turbulent forced convective mass (heat) transfer downstream of blockages with round and elongated holes in a rectangular channel was studied. The blockages and the channel had the same 12:1 (width-to-height ratio) cross section, and a distance equal to twice the channel height separated consecutive blockages. The diameter of the holes was either 0.5 or 0.75 of the height of the channel. Naphthalene sublimation experiments were conducted with four hole aspect ratios (hole-width-to-height ratios) between 1.0 and 3.4, two hole-to-channel area ratios (ratios of total hole cross-sectional area to channel cross-sectional area) of 0.2 and 0.3, and Reynolds numbers (based on the channel hydraulic diameter) of 7000 and 17,000. The effects of the hole aspect ratio, for each hole-to-channel area ratio, on the average mass (heat) transfer and the local mass (heat) transfer distribution on the exposed primary channel wall between consecutive blockages were examined. The results of the study showed that the blockages with holes caused the average mass (heat) transfer to be as high as about eight times that for fully developed turbulent flow through a smooth channel at the same mass flow rate. The elongated holes caused higher overall mass (heat) transfer and larger spanwise variation of the local mass (heat) transfer on the channel wall than round holes.

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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 test apparatus for mass transfer experiments (not to scale)

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Figure 2

Schematic of test section showing four blockages with elongated holes and naphthalene cassettes in top wall

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Figure 3

(a) Blockages with round or elongated holes; diameter of holes equals 12 of channel height. (b) Blockages with round or elongated holes; diameter of holes equals 34 of channel height.

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Figure 4

Local mass transfer distributions on three wall segments downstream of blockages with the smaller round holes, Case S-1

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Figure 5

Local mass transfer distributions on three wall segments downstream of blockages with the smaller elongated holes, Case S-4

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Figure 6

Local mass transfer distributions on three wall segments downstream of blockages with the larger round and elongated holes, Re=7000

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Figure 7

Local mass transfer distributions on second wall segment downstream of second blockage with the smaller holes, Cases S-1–S-4, for Re=17,000

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Figure 8

Local mass transfer distributions on second wall segment downstream of second blockage with the larger holes, Cases L-1–L-4, for Re=17,000

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Figure 9

Mass (heat) transfer enhancement on three wall segments between blockages with round holes and elongated holes with the largest aspect ratio

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Figure 10

Mass (heat) transfer enhancement on second wall segment between second and third blockages with round and elongated holes

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Figure 11

Pressure drop across two consecutive blockages with round and elongated holes

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Figure 12

Thermal performance based on mass transfer enhancement downstream of second blockage and pressure drop across two consecutive blockages

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