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Research Papers: Evaporation, Boiling, and Condensation

Experimental Measurements of Critical Heat Flux in Expanding Microchannel Arrays

[+] Author and Article Information
Mark J. Miner

e-mail: mark.miner@asu.edu

Patrick E. Phelan

e-mail: phelan@asu.edu

Carlos A. Ortiz

Department of Mechanical Engineering,
Arizona State University,
Tempe, AZ 85287-6106

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received November 13, 2012; final manuscript received April 25, 2013; published online August 19, 2013. Assoc. Editor: W. Q. Tao.

J. Heat Transfer 135(10), 101501 (Aug 19, 2013) (8 pages) Paper No: HT-12-1606; doi: 10.1115/1.4024388 History: Received November 13, 2012; Revised April 25, 2013

The effect of an expanding microchannel cross-section on flow boiling critical heat flux (CHF) is experimentally investigated across four rates of expansion. A pumped-loop apparatus is developed to boil R-134a in an array of microchannels cut into copper; a test section is designed to facilitate interchange of the microchannel specimens, allowing consistency across experiments. An optimum expansion angle allowing maximum heat flux is observed, the location of which increases with the mass flow rate. The boiling number does not indicate any optimum in the range observed, showing a nearly monotonic increase with expansion angle. The familiar increase in critical heat flux with mass flux is observed, though expansion shifts the CHF-mass flux curves in a favorable direction. The existence of an optimum expansion angle confirms an earlier qualitative hypothesis by the authors and suggests that microchannel heat sinks offer opportunities for methodical improvement of flow boiling stability and performance.

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References

Figures

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Fig. 1

Microchannel turret

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Fig. 2

Expanding channel schematic

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Fig. 3

Points of interest for dimension measurements in Table 1

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Fig. 4

Cutaway view of test section

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Fig. 5

Turret housing and plenum block

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Fig. 6

Flow loop schematic

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Fig. 7

Qin and TC-B profile, 0.369 deg channels, 3 g/s flow

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Fig. 8

Heat–cool cycles for losses

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Fig. 9

Thermocouple locations

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Fig. 10

Optimum expansion with mean lines

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Fig. 11

CHF versus mass flux

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Fig. 12

Average boiling number with linear fits and 95% confidence bounds

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Fig. 13

Experiment-averaged inlet subcooling

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Fig. 14

Damage at straight-channel outlet

Tables

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