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Research Papers: Evaporation, Boiling, and Condensation

Momentum Conservation and Condensing Vapor Bubbles

[+] Author and Article Information
I. Eames

 University College London, Torrington Place, London WC1E 7JE, UK

There were three anomalous data points, where Rv/a03. On further examination, we found that the bubbles were shrinking while in contact with the wall, so that they were much smaller on detachment from the sediment layer (a00.03cm) than the rest of the data set, where a0=0.10.2cm, and were omitted.

J. Heat Transfer 132(9), 091501 (Jun 23, 2010) (9 pages) doi:10.1115/1.4001604 History: Received March 25, 2008; Revised February 11, 2010; Published June 23, 2010; Online June 23, 2010

Boiling is a common feature of many daily processes, such as making tea, cooking, and heating. The growth, rise, collapse, and final disappearance of vapor bubbles are ubiquitous features of nucleate boiling. New experimental observations show that a vortex is generated as a consequence of the bubble disappearing. We categorize the possible mechanisms that lead to the generation of a vortex by bubbles. When the bubble collapses but does not change topology, the vortex is created by viscous effects, where the attached wake behind the vapor bubble persists after the bubble has disappeared. But when the bubbles collapse so rapidly that they change topology, the vortex is created by an inviscid mechanism. The total momentum communicated to the flow by the collapse processes is calculated and compared with the measurements of the vortex impulse.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Experimental observations of the collapse of a vapor bubble for collapse times (a) tc=0.014 s and (b) tc=0.003 s when ΔT=30 deg

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Figure 2

Qualitative visualization of the vortex generated using PIV. The two examples are (a) a bubble of radius a0=0.136 cm, collapsing without a topological change in tc=0.0055 s and (b) a bubble of initial radius a0=0.167 cm collapsing in tc=0.0058 s through a topological change.

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Figure 3

Characteristics of the vortex generated: (a) height as a function of time and (b) radius as a function of time. The symbols corresponds to ○ (a0=0.147 cm, tc=0.011 s), + (a0=0.129 cm, tc=0.050 s), ▷ (a0=0.110 cm, tc=0.048 s), ◁ (a0=0.163 cm, tc=0.011 s), △ (a0=0.0989 cm, tc=0.0018 s), and ∗ (a0=0.193, tc=0.0073 s).

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Figure 4

Schematic of the control volume used in Sec. 3 to analyze the conservation of momentum in an unbounded flow

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Figure 5

Summary of the three mechanisms of communicating bound vorticity into the fluid interior (a) inviscid topological mechanism, (b) inviscid through-surface flow, and (c) viscous mechanism

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Figure 6

The bulk measure of the destabilizing effect of gravity IE is plotted versus the maximum value of measure Imax calculated numerically over the bubble lifetime. The symbols + and ○ corresponds to bubbles of initial radius a0=0.1 and 0.2, respectively. The symbols correspond to the varying collapse times tc/tr=0.2,0.3,…,1.

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Figure 7

Phase diagram showing when the topological mechanism of collapse occurs (○) and when it does not (+). Equation 24 is plotted as a full line.

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Figure 8

Properties of the vortex: the variation in the vortex radius Rv and velocity Uv are shown in (a) and (b), respectively, as functions of tc/tr

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Figure 9

Ratio of the estimated momentum of the vortex (ME) to the measured vortex momentum (Mv)

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