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Research Papers

Surface Roughness Effects on Flow Boiling in Microchannels

[+] Author and Article Information
Benjamin J. Jones

NSF Cooling Technologies Research Center, School of Mechanical Engineering, and Birck Nanotechnology Center, Purdue University, 585 Purdue Mall, West Lafayette, IN 47907-2088

Suresh V. Garimella1

NSF Cooling Technologies Research Center, School of Mechanical Engineering, and Birck Nanotechnology Center, Purdue University, 585 Purdue Mall, West Lafayette, IN 47907-2088sureshg@purdue.edu

1

Corresponding author.

J. Thermal Sci. Eng. Appl 1(4), 041007 (Jun 24, 2010) (9 pages) doi:10.1115/1.4001804 History: Received May 18, 2009; Revised February 26, 2010; Published June 24, 2010; Online June 24, 2010

The influence of surface roughness on flow boiling heat transfer and pressure drop in microchannels is experimentally explored. The microchannel heat sink employed in the study consists of ten parallel, 25.4 mm long channels with nominal dimensions of 500×500μm2. The channels were produced by saw-cutting. Two of the test piece surfaces were roughened to varying degrees with electrical discharge machining (EDM). The roughness average Ra varied from 1.4μm for the as-fabricated, saw-cut surface to 3.9μm and 6.7μm for the two roughened EDM surfaces. Deionized water was used as the working fluid. The experiments indicate that the surface roughness has little influence on boiling incipience and only a minor impact on saturated boiling heat transfer coefficients at lower heat fluxes. For wall heat fluxes above 1500kW/m2, the two EDM surfaces (3.9μm and 6.7μm) have similar heat transfer coefficients that were 20–35% higher than those measured for the saw-cut surface (1.4μm). A modified Bertsch [2009, “A Composite Heat Transfer Correlation for Saturated Flow Boiling in Small Channels,” Int. J. Heat Mass Transfer, 52, pp. 2110–2118] correlation was found to provide acceptable predictions of the flow boiling heat transfer coefficient over the range of conditions tested. Analysis of the pressure drop measurements indicates that only the roughest surface (6.7μm) has an adverse effect on the two-phase pressure drop.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental flow loop

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Figure 2

Schematic of experimental test section

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Figure 3

Topographies of bottom channel surface

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Figure 4

Profiles of bottom channel surface

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Figure 5

Flow boiling curves for different surface conditions at different mass fluxes

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Figure 6

Critical heat flux versus surface roughness at two different mass fluxes

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Figure 7

Influence of surface roughness on saturated heat transfer coefficients at different mass fluxes

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Figure 8

Comparison of experimental measurements of saturated heat transfer coefficients with predictions

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Figure 9

Influence of surface roughness on channel pressure drop at different mass fluxes

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Figure 10

Comparison of experimental pressure drop results to those of Lee and Garimella (9)

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