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RESEARCH PAPERS: Boiling, Condensation, and Evaporation

On the Gas Entrapment and Nucleation Site Density During Pool Boiling of Saturated Water

[+] Author and Article Information
C. H. Wang, V. K. Dhir

Mechanical, Aerospace, and Nuclear Engineering Department, School of Engineering and Applied Science, University of California, Los Angeles, Los Angeles, CA 90024

J. Heat Transfer 115(3), 670-679 (Aug 01, 1993) (10 pages) doi:10.1115/1.2910738 History: Received May 01, 1992; Revised December 01, 1992; Online May 23, 2008

Abstract

A model to describe the effect of wettability on nucleation site density is presented. First, from Helmholtz free energy analysis, a criterion for the entrapment condition in a uniform temperature field is developed. Second, the stability condition of preexisting gas/vapor nuclei during the heating process and the minimum superheat required to initiate nucleation are determined. The prediction of the entrapment condition and the incipient temperature are consistent with the experimental observations made on surfaces having naturally existing cavities. Third, a naturally formed cavity on a heater surface is modeled as a spherical cavity. The cumulative active nucleation site density for a specified contact angle is expressed in terms of the cumulative density of cavities existing on the surface as Na = Pas · Nas where Nas is the heater surface cumulative cavity density with cavity mouth angles less than a specified value and Pas is a function of contact angle and cavity mouth angle. The model successfully predicts active site densities for different contact angles.

Copyright © 1993 by The American Society of Mechanical Engineers
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