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Research Papers: Heat Transfer Enhancement

Heat Transfer and Pressure Drop Correlations for Square Channels With V-Shaped Ribs at High Reynolds Numbers

[+] Author and Article Information
Nawaf Y. Alkhamis, Akhilesh P. Rallabandi, Je-Chin Han

Turbine Heat Transfer Laboratory,  Texas A&M University, College Station, TX 77843-3123jc-han@tamu.edu

J. Heat Transfer 133(11), 111901 (Sep 16, 2011) (8 pages) doi:10.1115/1.4004207 History: Received September 01, 2010; Revised April 16, 2011; Published September 16, 2011; Online September 16, 2011

Heat transfer coefficients and friction factors are measured in a 45 deg V-shaped rib roughened square duct at high Reynolds numbers, pertaining to internal passages of land-based gas turbine engines. Reynolds numbers in this study range from 30,000 to 400,000, which is much higher than prior studies of V-shaped rib roughened channels. The dimensions of the channel are selected to ensure that the flow is in the incompressible regime. Blockage ratio e/D ranges from 0.1 to 0.18 and the spacing ratio P/e ranges from 5 to 10. Reported heat transfer coefficients are regionally averaged, measured by isothermal copper plates. Results show that the heat transfer enhancement decreases with increasing Reynolds number. The friction factor is found to be independent of the Reynolds number. The thermal performance decreases when the Reynolds number increases. 45 deg V-shaped ribs show a higher thermal performance than corresponding 45 deg angled ribs, consistent with the trend established in literature. Correlations for the Nusselt number and the friction factor as function of Re, e/D, and P/e are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+ ).

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 9

Measured Nusselt numbers normalized by correlation for the 45 deg parallel ribs

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Figure 10

Schematic of secondary flow created by: (a) angled ribs and (b) V-shaped ribs

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Figure 2

Detailed internal view of the test section. Each layer (insulation and Plexiglas) is 1 in. thick.

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Figure 3

Linear regression used to determine friction factor

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Figure 11

Friction factors for various tested rib configurations

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Figure 12

Measured friction factors normalized with correlation for 45 deg angled ribs

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Figure 13

Ribbed side average Nusselt number enhancement ratio plotted against friction factor penalty ratio

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Figure 1

Schematic of flow loop

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Figure 4

Normalized Nusselt number ratios measured for smooth channel

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Figure 5

Local normalized Nusselt number ratio for: (a) P/e = 5 e/D = 0.1, (b) P/e = 7.5 e/D = 0.1, (c) P/e = 10 e/D = 0.1, (d) P/e = 5 e/D = 0.15, (e) P/e = 7.5 e/D = 0.15, (f) P/e = 10 e/D = 0.15, (g) P/e = 5 e/D = 0.18, (h) P/e = 7.5 e/D = 0.18, (i) P/e = 5 e/D = 0.18

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Figure 6

Schematic of flow over V-shaped ribs indicating the effect of rib spacing for rib height

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Figure 7

Average normalized Nusselt number plotted against Reynolds number

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Figure 8

Fully developed ribbed side averaged Nusselt number obtained for various test cases

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Figure 14

Thermal performance plotted against Reynolds number

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Figure 15

Friction roughness function plotted with roughness Reynolds number, e+

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Figure 16

Heat transfer roughness function plotted with roughness Reynolds number

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