Pool Boiling Using Thin Enhanced Structures Under Top-Confined Conditions

[+] Author and Article Information
Camil-Daniel Ghiu

G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332

Yogendra K. Joshi

G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332yogendra.joshi@me.gatech.edu

J. Heat Transfer 128(12), 1302-1311 (Jun 16, 2006) (10 pages) doi:10.1115/1.2349503 History: Received October 14, 2005; Revised June 16, 2006

An experimental study of pool boiling using enhanced structures under top-confined conditions was conducted with a dielectric fluorocarbon liquid (PF 5060). The single layer enhanced structures studied were fabricated in copper and quartz, had an overall size of 10×10mm2, and were 1mm thick. The parameters investigated in this study were the heat flux (0.834Wcm2) and the top space S(013mm). High-speed visualizations were performed to elucidate the liquid/vapor flow in the space above the structure. The enhancement observed for plain surfaces in the low heat fluxes regime is not present for the present enhanced structure. On the other hand, the maximum heat flux for a prescribed 85°C surface temperature limit increased with the increase of the top spacing, similar to the plain surfaces case. Two characteristic regimes of pool boiling have been identified and described: isolated flattened bubbles regime and coalesced bubbles regime.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Enhanced structures used in this study. (a) Frontal view of structure C-0.105-0.7. (b) Magnified micrographs of two top channels of the structure C-0.105-0.7. (c) Pore formation at the intersection of microchannels. (d) Magnified lateral view of the quartz structure Q-0.200-0.7. (e) Magnified top view of the quartz structure Q-0.200-0.7.

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Figure 2

Schematic of the setup: (a) heater assembly and (b) boiling chamber with the visualization tube

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Figure 3

Boiling curves for various top gaps. The lines delineate the observed flow regimes.

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Figure 4

Comparison between present data and Chien and Chen (12) data.

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Figure 5

Temperature traces at steady state (structure C-0.105-0.7, q″=12W∕cm2). (a) S=0.35mm. (b) S=1mm. (c) S=1.75mm. (d) S=13mm.

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Figure 6

Visualization of boiling for top gap S=1.75mm. (a) Individual bubbles are present, q″=0.8W∕cm2. (b) Coalescence occurs producing bubble clusters, q″=5.7W∕cm2. (c) Almost entire space is filled with vapor, q″=14.5W∕cm2. (d) Vapor filled space with a wavy interface, q″=24.4W∕cm2.

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Figure 7

Visualization of boiling for top gap S=1mm. (a) Vapor covers portions of the top surface, q″=0.9W∕cm2. (b) Individual bubbles are feeding the vapor formations from below, q″=5.6W∕cm2. (c) Higher magnification view of the top channels, q″=14.5W∕cm2. (d) Boiling phenomena at the highest tested heat flux, q″=18.3W∕cm2.

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Figure 8

Visualization of boiling for top gap S=0.7mm. (a) Lateral view of two bubbles entering the vapor mass, q″=0.8W∕cm2. (b) Coalesced vapor formations occupy much of the top space, q″=3.8W∕cm2. (c) Wavy interface, droplets on top surface, q″=7.6W∕cm2. (d) Liquid plugs entrapped in the vapor mass, q″=16.5W∕cm2.

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Figure 9

Visualization of boiling for top gap S=0.35mm. (a) Growth and coalescence of two individual bubbles, q″=0.9W∕cm2. (b) Thin liquid films forming on the top surface, q″=5.8W∕cm2. (c) Thin liquid film edges and liquid plugs, q″=14.3W/cm2.

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Figure 10

Visualization of boiling for structure Q-0.200-0.7. (a) A few flattened vapor bubbles rise above the structure, q″=1.8W∕cm2. (b) Vapor slug forming inside a bottom channel, q″=1.8W∕cm2. (c) Deformed vapor bubbles reside in the top channels, q″=3.8W∕cm2. (d) Vapor fills the entire gap space, q″=4.8W∕cm2.



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