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RESEARCH PAPERS: Micro/Nanoscale Heat Transfer

Local Heat Transfer Measurements in Microchannels Using Liquid Crystal Thermography: Methodology Development and Validation

[+] Author and Article Information
R. Muwanga

Department of Mechanical and Industrial Engineering,  Concordia University, 1515 St. Catherine W., Montreal, Quebec, Canada, H3G 2W1rmuwanga@alcor.concordia.ca

I. Hassan1

Department of Mechanical and Industrial Engineering,  Concordia University, 1515 St. Catherine W., Montreal, Quebec, Canada, H3G 2W1ibrahimH@alcor.concordia.ca

1

Author to whom all correspondence should be addressed

J. Heat Transfer 128(7), 617-626 (Dec 14, 2005) (10 pages) doi:10.1115/1.2193541 History: Received April 12, 2005; Revised December 14, 2005

Microchannel heat transfer governs the performance of the microchannel heat sink, which is a recent technology aimed at managing the stringent thermal requirements of today’s high-end electronics. The microencapsulated form of liquid crystals has been well established for use in surface temperature mapping, while limited studies are available on the use of the un-encapsulated form. This latter form is advantageous since it offers the potential for high spatial resolution, which is necessary for microgeometries. A technique for using un-encapsulated thermochromic liquid crystals (TLCs) in order to measure the local heat transfer coefficient in microchannel geometries is shown in the present study. Measurements were made in a closed loop facility combined with a microscopic imaging system and automated data acquisition. A localized TLC calibration was used to account for a non-uniform coating and variation of lighting conditions. Three test section configurations were investigated with each subsequent configuration arising due to a shortfall in the previous. Two of these configurations are comprised of single wall heated rectangular channels, while the third is a circular tube channel. Validation results are also presented; overall, the methods developed and utilized in this study have been shown to provide the local heat transfer coefficient in microchannels.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the experimental test facility

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Figure 2

Configuration for Test Module I

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Figure 3

Configuration for Test Module II

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Figure 4

Configuration for Test Module III—circular tube

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Figure 5

Schematic of the data acquisition system

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Figure 6

Schematic of the image acquisition system

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Figure 7

Constant temperature region hue angle histogram

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Figure 8

Corrected calibration curve with fifth order and third order fits

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Figure 9

Typical calibration curve fits at a fixed image location for a number of tube locations

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Figure 10

Typical good-fit calibration curve

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Figure 11

Calibration curves accumulated over different time periods

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Figure 12

Sample measured wall temperature and calculated fluid bulk temperature

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Figure 13

Streamwise averaged Nusselt numbers for laminar flow cases

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Figure 14

Streamwise averaged Nusselt numbers for varying flow rates

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Figure 15

Variation of the averaged Nusselt number with Reynolds number with comparison to correlations

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