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RESEARCH PAPERS: Evaporation, Boiling, and Condensation

Effect of Surface Orientation on Nucleate Boiling of FC-72 on Porous Graphite

[+] Author and Article Information
Jack L. Parker

Institute for Space and Nuclear Power Studies and Chemical and Nuclear Engineering Department, The University of New Mexico, Albuquerque, NM 87131

Mohamed S. El-Genk1

Institute for Space and Nuclear Power Studies and Chemical and Nuclear Engineering Department, The University of New Mexico, Albuquerque, NM 87131mgenk@unm.edu

1

Corresponding author; Regents’ Professor of Chemical and Nuclear Engineering and Director of Institute for Space and Nuclear Power Studies.

J. Heat Transfer 128(11), 1159-1175 (Mar 13, 2006) (17 pages) doi:10.1115/1.2352783 History: Received August 11, 2005; Revised March 13, 2006

Effects of orientations of porous graphite and smooth copper surfaces, measuring 10mm×10mm, on saturation nucleate boiling and critical heat flux (CHF) of FC-72 dielectric liquid and of liquid subcooling (0, 10, 20, and 30K) on nucleate boiling in the upward facing orientation are investigated. Inclination angles (θ) considered are 0deg (upward-facing), 60, 90, 120, 150, and 180deg (downward facing). The values of nucleate boiling heat flux, nucleate boiling heat transfer coefficient (NBHTC), and CHF are compared with those measured on the smooth copper surface of the same dimensions and CHF values on both copper and porous graphite are compared with those reported by other investigators on the smooth surfaces and microporous coatings. Results demonstrated higher NBHTC and CHF on porous graphite, particularly in the downward-facing orientation (θ=180deg). In the upward-facing orientation, NBHTCs on both surfaces decrease with increased subcooling, but increase with increased surface superheat reaching maxima then decrease with further increase in surface superheat. In saturation boiling on copper and both saturation and subcooled boiling on porous graphite these maxima occur at or near the end of the discrete bubble region, and near CHF in subcooled boiling on copper. Maximum saturation NBHTC on porous graphite increases with decreased surface superheat and inclination angle, while that on copper increases with increased surface superheat and decreased surface inclination. At low surface superheats, saturation nucleate boiling heat flux increases with increased inclination, but decreases with increased inclination at high surface superheats, consistent with previously reported data for dielectric and nondielectric liquids. The fractional decreases in saturation CHF with increased θ on smooth copper and microporous coatings are almost identical, but markedly larger than on porous graphite, particularly in the downward-facing orientation. In this orientation, saturation CHF on porous graphite of 16Wcm2 is much higher than on copper (4.9Wcm2) and as much as 53% of that in the upward-facing orientation, compared to only 18% on copper.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

SEM images of porous graphite

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Figure 2

SEM images of copper surface

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Figure 3

Effect of aging on pool boiling of FC-72 on porous graphite

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Figure 4

Comparison of saturation pool boiling curves of FC-72 liquid at different inclinations on smooth copper and aged porous graphite

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Figure 5

Saturation boiling curves of FC-72 on porous graphite and copper at different inclinations

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Figure 6

Effect of surface orientation on saturation NBHTC of FC-72 on aged porous graphite and on copper

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Figure 7

Effect of surface orientation on maximum NBHTC and Nusselt number of FC-72 on aged porous graphite and on copper

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Figure 8

Dependences of maximum NBHTC and Nusselt number of FC-72 on aged porous graphite and copper on surface orientation

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Figure 9

Ratios of saturation NBHTC of FC-72 on porous graphite and copper

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Figure 10

Saturation boiling curve and photographs on aged porous graphite in upward facing orientation

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Figure 11

Saturation boiling curve and photographs on aged porous graphite in vertical orientation

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Figure 12

Saturation boiling curve and photographs on aged porous graphite in downward-facing orientation

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Figure 13

Saturation boiling photographs on aged porous graphite in vertical orientation

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Figure 14

Saturation boiling photographs on aged porous graphite in 150deg orientation

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Figure 15

Effect of subcooling on nucleate boiling of FC-72 on copper in upward-facing orientation

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Figure 16

Effect of subcooling on nucleate boiling of FC-72 on unaged porous graphite in upward facing orientation

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Figure 17

Effect of inclination angle on saturation CHF of FC-72 on different surfaces

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Figure 18

Saturation CHF coefficients for FC-72 on different surfaces

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Figure 19

Inclination coefficients of saturation CHF of FC-72 on different surfaces

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Figure 20

Ratios of saturation CHF of FC-72 on porous graphite and microporous coatings to that measured on copper

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