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RESEARCH PAPERS: Evaporation, Boiling, and Condensation

Effects of Gap Geometry and Gravity on Boiling Around a Constrained Bubble in 2-Propanol/Water Mixtures

[+] Author and Article Information
Chen-li Sun1

Department of Mechanical Engineering,  National Taiwan University of Science and Technology, 43 Sec. 4 Keelung Rd., Taipei, 106, Taiwanclsun@mail.ntust.edu.tw

Van P. Carey

Department of Mechanical Engineering,  University of California, Berkeley, Berkeley, CA 94720-1740vcarey@me.berkeley.edu

1

Corresponding author.

J. Heat Transfer 129(2), 114-123 (May 15, 2006) (10 pages) doi:10.1115/1.2402178 History: Received October 10, 2005; Revised May 15, 2006

In this study, boiling experiments were conducted with 2-propanol/water mixtures in confined gap geometry under various levels of gravity. The temperature field created within the parallel plate gap resulted in evaporation over the portion of the vapor-liquid interface of the bubble near the heated surface, and condensation near the cold surface. Full boiling curves were obtained and two boiling regimes—nucleate boiling and pseudofilm boiling—and the transition condition, the critical heat flux (CHF), were identified. The observations indicated that the presence of the gap geometry pushed the nucleate boiling regime to a lower superheated temperature range, resulting in correspondingly lower heat flux. With further increases of wall superheat, the vapor generated by the boiling process was trapped in the gap to blanket the heated surface. This caused premature occurrence of CHF conditions and deterioration of heat transfer in the pseudo-film boiling regime. The influence of the confined space was particularly significant when greater Marangoni forces were present under reduced gravity conditions. The CHF value of x (molar fraction)=0.025, which corresponded to weaker Marangoni forces, was found to be greater than that of x=0.015 with a 6.4mm gap.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 5

Boiling curve of distilled water under various gravity levels, x=0, gap=6.4mm (solid symbols represent the nucleate boiling regime, while open symbols represent the pseudofilm boiling regime)

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Figure 6

Boiling curve of 2-propanol/water mixtures under various gravity levels, x=0.015, gap=6.4mm (solid symbols represent the nucleate boiling regime, while open symbols represent the pseudo-film boiling regime)

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Figure 7

Boiling curve of 2-propanol/water mixtures under various gravity levels, x=0.015, gap=12.7mm (solid symbols represent the nucleate boiling regime, while open symbols represent the pseudo film boiling regime)

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Figure 8

Boiling curve of 2-propanol/water mixtures under various gravity levels, x=0.025, gap=6.4mm (solid symbols represent the nucleate boiling regime, while open symbols represent the pseudo-film boiling regime)

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Figure 9

Comparison of gravity dependency on heat transfer coefficients in nucleate boiling to the Rohsenow correlation (n=0.5 in Eq. 2), x=0.015. Heat transfer coefficients were calculated at q″=40W∕cm2 for gap=6.4mm, and q″=250W∕cm2 for pool boiling (no gap) from (22)

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Figure 11

Comparison of gravity dependency on heat transfer coefficients in pseudofilm boiling, gap=6.4mm

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Figure 10

Comparison of gravity dependency on CHF, x=0.015

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Figure 2

Test section (a) side view, (b) 3D drawing

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Figure 4

Boiling regimes for 2-propanol/water mixtures with the gap constraint

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Figure 3

Dimension of (a) holding flange (v), (b) heater element (i), (c) condenser (ii)

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Figure 1

(a) Surface tension versus molar fraction, (b) absolute value of the Marangoni parameter [16] versus molar fraction for 2-propanol/water mixtures at bubble point temperature, P=5kPa

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