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TECHNICAL PAPERS: Evaporation, Boiling, and Condensation

A Flow Boiling Heat Transfer Investigation of FC-72 in a Microtube Using Liquid Crystal Thermography

[+] Author and Article Information
R. Muwanga

Department of Mechanical and Industrial Engineering, Concordia University, Montreal, Quebec H3G 1M8, Canada

I. Hassan

Department of Mechanical and Industrial Engineering, Concordia University, Montreal, Quebec H3G 1M8, CanadaibrahimH@alcor.concordia.ca

J. Heat Transfer 129(8), 977-987 (Dec 06, 2006) (11 pages) doi:10.1115/1.2728905 History: Received November 01, 2005; Revised December 06, 2006

This paper presents experimental measurements of boiling heat transfer in a 1.067 mm inner diameter tube, using liquid crystal thermography for wall temperature measurement. The study was motivated by the two-phase microchannel pumped cooling loop, a recent technology proposed for thermal management of tomorrow's high-end electronics. The working fluid was FC-72, which is a dielectric coolant and measurements were obtained in a closed loop test facility. A unique flow boiling onset was observed whereby a large wall temperature gradient travels along the tube. During flow boiling conditions, wall temperature fluctuations have been observed. The use of a thermographic technique has added insight into the flow boiling characteristics and acts as a partial flow visualization method. Local heat transfer coefficients are presented and compared with correlations for both macro- and microchannels. The heat transfer coefficient is found to be influenced by the heat flux at a lower mass flux but only mildly at a higher mass flux.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 2

Test section module

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Figure 3

Schematic of the data acquisition system

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Figure 4

Schematic of the image acquisition system

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Figure 5

(a), (c) Heat flux versus wall temperature, measured by embedded thermocouple; and (b), (d) pressure drop versus heat flux

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Figure 6

(Color) TLC wall temperature visualization over time during boiling onset, 79–88 z∕D, Q∕Ah∼30.4kW∕m2, G∼770kg∕(m2s). Red is lower temperature region, and flow is from left to right

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Figure 7

TLC wall temperature time trace—three separate locations imaged at separate time instants, Q∕Ah∼50.7kW∕m2, G∼770kg∕(m2s)

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Figure 8

Typical power spectrum of oscillating wall temperature as measured by TLC, for corresponding wave forms in Fig. 7, Q∕Ah∼50.7kW∕m2, G∼770kg∕(m2s)

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Figure 9

(Color) Wall temperature fluctuations highlighting oscillatory behavior and high wall temperature gradient front. Red is cool and blue is hot, black is high temperature past the clearing point of the TLC. Covering a time span of 0.3s, at 78–88 z∕D and Q∕Ah∼79kW∕m2, G∼770kg∕(m2s), and flow is from left to right.

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Figure 10

Circumferentially averaged wall temperature measurement and calculated fluid bulk temperature along tube for varying heat fluxes, G∼770kg∕(m2s)

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Figure 11

Local heat transfer coefficient as a function of quality, effect of heat flux, and mass flux

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Figure 12

Local heat transfer coefficient, comparison with correlation at various heat fluxes, G∼770kg∕(m2s)

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Figure 13

Local heat transfer coefficient, comparison with correlation at various heat fluxes, G∼1043kg∕(m2s)

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