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TECHNICAL PAPERS: Evaporation, Boiling, and Condensation

Heterogeneous Nucleation With Artificial Cavities

[+] Author and Article Information
Yusen Qi

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

James F. Klausner

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

J. Heat Transfer 127(11), 1189-1196 (May 27, 2005) (8 pages) doi:10.1115/1.2039111 History: Received January 06, 2005; Revised May 27, 2005

Bubble incipience in artificial cavities manufactured from silicon has been studied using gas nucleation and pool boiling. Moderately wetting water and highly wetting ethanol have both been used as the bulk fluid with cylindrical cavities, as well as those with a triangle, square, and rectangle shape cross section. Nominal cavity sizes range from 8to60μm. The incipience conditions observed for water using both gas nucleation and pool boiling suggest that bubble initiation originates from a concave meniscus. Cornwell’s contact angle hysteresis theory for vapor-trapping cavities is used to explain the gas nucleation results. The pool boiling results are more difficult to explain. Using ethanol, cavities appeared to be completely flooded and were not activated using either gas nucleation or pool boiling. Using water and gas nucleation, cavities were almost always activated, provided the incipience criterion was satisfied; in contrast cavities in pool boiling with water activated with different superheats during different experiments. The difference in incipience behavior between gas nucleation and pool boiling with water is explained based on vapor-trapping and thermal suppression considerations. Based on limited experimental results, it appears that the backpressure does not influence gas bubble incipience, provided the pressure difference is the same. The experimental results presented affirm the theory of heterogeneous nucleation from vapor-trapping cavities provided contact angle hysteresis and vapor trapping are fully accounted for. However, the results also suggest that the theoretical considerations required for a deterministic model for incipience from vapor-trapping cavities during boiling is more complex than previously hypothesized.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Convex vapor meniscus protruding from a cylindrical cavity

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Figure 2

Schematic drawing of liquid∕vapor interface

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Figure 3

Schematic diagram of gas nucleation facility

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Figure 4

Assembled view of pool boiling chamber

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Figure 5

Two-dimensional measurement of cylindrical cavity with 60μm mouth diameter and 45μm depth

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Figure 6

Layout of cylindrical cavities on silicon surface

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Figure 7

The influence of backpressure on gas bubble activation

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Figure 8

Typical images of bubble activation on cavities with different diameters

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Figure 9

Comparison between measured and predicted gas bubble incipience

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Figure 10

Comparison between measured and predicted boiling incipience

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Figure 11

Gas bubble activation on a 10×10 matrix of 10‐μm cylindrical cavities

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Figure 12

Gas bubble activation on cavities with different shapes

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Figure 13

The influence of cavity shape on gas bubble activation

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Figure 14

Vapor-trapping mechanism in cylindrical cavities

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