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Research Papers

The Influence of Surface Roughness on Nucleate Pool Boiling Heat Transfer

[+] Author and Article Information
Benjamin J. Jones, John P. McHale

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. Heat Transfer 131(12), 121009 (Oct 15, 2009) (14 pages) doi:10.1115/1.3220144 History: Received April 15, 2008; Revised May 06, 2009; Published October 15, 2009

The effect of surface roughness on pool boiling heat transfer is experimentally explored over a wide range of roughness values in water and Fluorinert™ FC-77, two fluids with different thermal properties and wetting characteristics. The test surfaces ranged from a polished surface (Ra between 0.027μm and 0.038μm) to electrical discharge machined (EDM) surfaces with a roughness (Ra) ranging from 1.08μm to 10.0μm. Different trends were observed in the heat transfer coefficient with respect to the surface roughness between the two fluids on the same set of surfaces. For FC-77, the heat transfer coefficient was found to continually increase with increasing roughness. For water, on the other hand, EDM surfaces of intermediate roughness displayed similar heat transfer coefficients that were higher than for the polished surface, while the roughest surface showed the highest heat transfer coefficients. The heat transfer coefficients were more strongly influenced by surface roughness with FC-77 than with water. For FC-77, the roughest surface produced 210% higher heat transfer coefficients than the polished surface while for water, a more modest 100% enhancement was measured between the same set of surfaces. Although the results highlight the inadequacy of characterizing nucleate pool boiling data using Ra, the observed effect of roughness was correlated using hRam as has been done in several prior studies. The experimental results were compared with predictions from several widely used correlations in the literature.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Schematic of pool boiling facility and (b) top view of test block showing the locations of thermocouples and cartridge heaters

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Figure 2

Surface topography of test surfaces over an area of 400×300 μm2 as measured by an optical profilometer: (a) 0.038 μm polished surface, (b) 1.08 μm EDM surface, (c) 2.22 μm EDM surface, and (d) 5.89 μm EDM surface

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Figure 3

Boiling curves for water: (a) heat flux versus wall superheat and (b) heat transfer coefficient versus heat flux

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Figure 4

Boiling curves for FC-77: (a) heat flux versus wall superheat and (b) heat transfer coefficient versus heat flux

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Figure 5

Boiling curves showing the hysteresis effect for (a) water and (b) FC-77, where q↑ indicates data obtained in order of increasing heat flux and q↓ indicates those in order of decreasing heat flux. It is noted that a smaller heat flux increment was used experimentally than is indicated in (b); only a fraction of the data are included to improve readability of the figure.

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Figure 6

Photographs of the boiling process in water for varying heat flux and surface roughness. The physical width of each image is approximately 25 mm.

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Figure 7

Photographs of the boiling process in FC-77 for varying heat flux and surface roughness. The physical width of each image is approximately 7.3 mm.

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Figure 8

Dependence of heat transfer coefficient on surface roughness for (a) water and (b) FC-77. The solid lines represent a curve fit through all five experimental data points (one polished surface and four EDM surfaces). The dashed lines in (b) represent a curve fit to only the four EDM surfaces (excluding the 0.027 μm polished surface).

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Figure 9

Dependence of heat flux exponent n in the relationship h∝qn on surface roughness

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Figure 10

Comparison between experimental data and predictions from the Cooper correlation (32-33) for (a) water and (b) FC-77

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Figure 11

Comparison between experimental data and predictions from the Gorenflo correlation (34) for (a) water and (b) FC-77

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Figure 12

Comparison between experimental data and predictions from the Leiner correlation (59) for (a) water and (b) FC-77

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