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TECHNICAL PAPERS: Evaporation, Boiling, and Condensation

Homogeneous Nucleation of Vapor at Preferred Sites During Rapid Transient Heating of Liquid in Micropassages

[+] Author and Article Information
Van P. Carey

Mechanical Engineering Department, University of California Berkeley, Berkeley, CA 94720-1776vcarey@me.berkeley.edu

Jorge Padilla, Yu Gan

Mechanical Engineering Department, University of California Berkeley, Berkeley, CA 94720-1776

J. Heat Transfer 129(10), 1333-1340 (Dec 09, 2006) (8 pages) doi:10.1115/1.2754989 History: Received September 08, 2006; Revised December 09, 2006

Rapid heating of a liquid at the wall of a micropassage may produce homogeneous nucleation of vapor in the liquid in contact with the surface. In such circumstances, nucleation is generally expected to be most likely to occur in the hottest liquid closest to the surface. It is known, however, that in many cases, the liquid molecules closest to the surface will experience long-range attractive forces to molecules in the solid, with the result that the equation of state for the liquid near the surface will differ from that for the bulk liquid. In micro- and nanopassages, this wall-affected region may be a significant fraction of the passage interior volume. Recent investigations of wall force effects on the liquid indicate that these forces increase the spinodal temperature in the near-surface region. The results of these previous investigations suggest that for heated surfaces with nanoscale roughness, protrusion of bulk fluid into crevices in the surface may make them preferred sites for homogeneous nucleation during rapid heating. A detailed model analysis of the heat transfer in a model conical crevice is developed and used to explore the plausibility and apparent mechanisms of preferred-site homogeneous nucleation. The analysis predicts that protrusion of bulk liquid into a conical cavity does, under some conditions, make the cavity a preferred site for the first occurrence of homogeneous nucleation. The analysis is used to examine the range of conditions under which a crevice will be a preferred site. The implications for nucleation near a solid surface during rapid heating are also explored for circumstances similar to those for bubble nucleation adjacent to heaters in microheater reservoirs in inkjet printer heads.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Prediction of reduced pressure and spinodal temperature with distance from the wall predicted by the model of Carey and Wemhoff (11). The wall is a gold (metal) surface.

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Figure 2

Schematic of near-wall temperature variation and the approach to the spinodal condition

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Figure 3

Schematic of the wall-affected region near a rough surface

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Figure 4

Computational domain and adjacent regions

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Figure 5

Dimensionless temperature field Φ(η,θ,t̂) when spinodal condition is reached at point X (t̂=527). The crevice sidewall (rc) is 30nm and the cone angle is 18.3deg (case I). The gray region adjacent to the solid surface is the wall-affected layer.

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Figure 6

Dimensionless temperature field Φ(η,θ,t̂) when spinodal condition is reached at point X (t̂=47.25). The crevice sidewall (rc) is 100nm and the cone angle is 18.3deg (case II). The gray region adjacent to the solid surface is the wall-affected layer.

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Figure 7

Variation of dimensionless temperature with dimensionless time (t̂=t∕tr) at points X and F. The crevice sidewall (rc) is 30nm and the cone angle is 18.3deg (case I).

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Figure 8

Variation of dimensionless temperature with dimensionless time (t̂=t∕tr) at points X and F. The crevice sidewall (rc) is 100nm and the cone angle is 18.3deg (case II).

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Figure 9

Variation of embryo generation rate J with temperature for water (the units on J are number∕m3s)

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