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RESEARCH PAPERS: Evaporation, Boiling, and Condensation

Comparison of Nucleation Site Density for Pool Boiling and Gas Nucleation

[+] Author and Article Information
Yusen Qi

 University of Florida, Department of Mechanical and Aerospace Engineering, P.O. Box 116300, Gainesville, FL 32611-6300

James F. Klausner1

 University of Florida, Department of Mechanical and Aerospace Engineering, P.O. Box 116300, Gainesville, FL 32611-6300

1

Corresponding author; e-mail: klaus@ufl.edu; tel.: 352-392-3506; fax: 352-392-1071.

J. Heat Transfer 128(1), 13-20 (May 27, 2005) (8 pages) doi:10.1115/1.2130399 History: Received October 07, 2004; Revised May 27, 2005

It has been well established that the rate of heat transfer associated with boiling systems is strongly dependent on the nucleation site density. Over many years attempts have been made to predict nucleation site density in boiling systems using a variety of techniques. With the exception of specially prepared surfaces, these attempts have met with little success. This paper presents an experimental investigation of nucleation site density measured on roughly polished brass and stainless steel surfaces for gas nucleation and pool boiling over a large parameter space. A statistical model used to predict the nucleation site density in saturated pool boiling is also investigated. The fluids used for this study, distilled water and ethanol, are moderately wetting and highly wetting, respectively. Using distilled water it has been observed that the trends of nucleation site density versus the inverse of the critical radius are similar for pool boiling and gas nucleation. The nucleation site density is higher for gas nucleation than for pool boiling. An unexpected result has been observed with ethanol as the heat transfer fluid, which casts doubt on the general assumption that heterogeneous nucleation in boiling systems is exclusively seeded by vapor trapping cavities. Due to flooding, few sites are active on the brass surface and at most two are active on the stainless steel surface during gas nucleation experiments. However, nucleation sites readily form in large concentration on both the brass and stainless steel surfaces during pool boiling. The pool boiling nucleation site densities for ethanol on rough and mirror polished brass surfaces are also compared. It shows that there is not a significant difference between the measured nucleation site densities on the smooth and rough surfaces. These results suggest that, in addition to vapor trapping cavities, another mechanism must exist to seed vapor bubble growth in boiling systems.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Gas nucleation facility

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Figure 2

Test section used in gas nucleation experiments

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Figure 3

Assembled view of pool boiling chamber

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Figure 4

Cylindrical heater and heat transfer surface used in pool boiling experiments

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Figure 5

A typical image of pool boiling nucleation sites

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Figure 6

Variation of nucleation site density for water on brass surface using gas nucleation and pool boiling

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Figure 7

Variation of nucleation site density for water on stainless steel surface using gas nucleation and pool boiling

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Figure 8

Comparison between measured and predicted nucleation site density on brass surface using water

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Figure 9

Comparison between measured and predicted nucleation site density on stainless steel surface using water

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Figure 10

Variation of nucleation site density for ethanol on brass surface using gas nucleation and pool boiling

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Figure 11

Variation of pool boiling nucleation site density for ethanol on brass surface

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Figure 12

Variation of pool boiling nucleation site density for ethanol on stainless steel surface

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Figure 13

Variation of pool boiling nucleation site density for ethanol on coarse and polished brass surfaces

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