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Forced Convection

An Experimental Investigation of Structured Roughness Effect on Heat Transfer During Single-Phase Liquid Flow at Microscale

[+] Author and Article Information
Ting-Yu Lin

Mechanical Engineering Department,  Rochester Institute of Technology, Rochester, NY 14623rittonylin@gmail.com

Satish G. Kandlikar1

Mechanical Engineering Department,  Rochester Institute of Technology, Rochester, NY 14623sgkeme@rit.edu

1

Corresponding author.

J. Heat Transfer 134(10), 101701 (Aug 07, 2012) (9 pages) doi:10.1115/1.4006844 History: Received May 13, 2011; Revised May 07, 2012; Published August 06, 2012; Online August 07, 2012

The effect of structured roughness on the heat transfer of water flowing through minichannels was experimentally investigated in this study. The test channels were formed by two 12.7 mm wide × 94.6 mm long stainless steel strips. Eight structured roughness elements were generated using a wire electrical discharge machining (EDM) process as lateral grooves of sinusoidal profile on the channel walls. The height of the roughness structures ranged from 18 μm to 96 μm, and the pitch was varied from 250 μm to 400 μm. The hydraulic diameter of the rectangular flow channels ranged from 0.71 mm to 1.87 mm, while the constricted hydraulic diameter (obtained by using the narrowest flow gap) ranged from 0.68 mm to 1.76 mm. After accounting for heat losses from the edges and end sections, the heat transfer coefficient for smooth channels was found to be in good agreement with the conventional correlations in the laminar entry region as well as in the laminar fully developed region. All roughness elements were found to enhance the heat transfer. In the ranges of parameters tested, the roughness element pitch was found to have almost no effect, while the heat transfer coefficient was significantly enhanced by increasing the roughness element height. An earlier transition from laminar to turbulent flow was observed with increasing relative roughness (ratio of roughness height to hydraulic diameter). For the roughness element designated as B-1 with a pitch of 250 μm, roughness height of 96 μm and a constricted hydraulic diameter of 690 μm, a maximum heat transfer enhancement of 377% was obtained, while the corresponding friction factor increase was 371% in the laminar fully developed region. Comparing different enhancement techniques reported in the literature, the highest roughness element tested in the present work resulted in the highest thermal performance factor, defined as the ratio of heat transfer enhancement factor (over smooth channels) and the corresponding friction enhancement factor to the power 1/3.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of the experimental setup (a) system overview (b) test section assembly

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Figure 2

Test surface profile for surface B-1 and B-2 obtained from Confocal Laser Scanning Microscope (a) three-dimensional view, (b) roughness profile cross section, (λ = 250 μm, H = 96.3 μm)

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Figure 3

A schematic illustrating axial conduction effect on fluid temperature distribution

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Figure 4

Comparison of experimental Nu in the center region of the test section to the prediction of conventional correlation of Harms [42]

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Figure 5

Comparison of Nu of rough channel (Channel D-2 ) normalized by theoretical developing flow heat transfer correlation by Harms [42]

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Figure 6

Effect of roughness element pitch on heat transfer enhancement in channels C-2 and D-2

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Figure 7

Effect of roughness element pitch on heat transfer for a roughness height about 35 μm; smaller hydraulic diameter channels C-1 and D-1 and larger hydraulic diameter channels C-2 and D-2

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Figure 8

Effect of roughness element height H on heat transfer for a roughness elements pitch of λ = 250 μm

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Figure 9

Effect of relative roughness element height H/Dh on heat transfer for a roughness elements pitch λ = 250 μm

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Figure 10

Comparison of Nu as a function of Re for channels B-1 , B-2 , and C-1 with λ = 250 μm

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Figure 11

Comparison of h as a function of Re for channels B-1 , B-2 , and C-1 with λ = 250 μm

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Figure 12

Comparison of friction factor f as a function of Re for B-1 , B-2 , and C-1 from Wagner and Kandlikar [40]

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Figure 13

Comparison of f and j (=StPr2/3 ) as a function of Re for B-1

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Figure 14

Comparison of enhancement factor η of B-1 with other available enhancement techniques from the recent literature [32-35]

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Figure 15

Friction factor f and Nu enhancement ratio of as a function of λ/H for all rough channels tested

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Figure 16

Friction factor f and Nu enhancement ratio of as a function of H/Dh for all rough channels tested

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