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Research Papers: Evaporation, Boiling, and Condensation

Confocal Microscopy for Capillary Film Measurements in a Flat Plate Heat Pipe

[+] Author and Article Information
Frédéric Lefèvre1

 Universite de Lyon, CNRS INSA-Lyon, CETHIL, UMR5008, F-69621,Villeurbanne, France Universite Lyon 1, F-69622, Francefrederic.lefevre@insa-lyon.fr

Romuald Rullière, Stéphane Lips, Jocelyn Bonjour

 Universite de Lyon, CNRS INSA-Lyon, CETHIL, UMR5008, F-69621,Villeurbanne, France Universite Lyon 1, F-69622, France

1

Corresponding author.

J. Heat Transfer 132(3), 031502 (Jan 04, 2010) (6 pages) doi:10.1115/1.4000057 History: Received April 21, 2009; Revised July 14, 2009; Published January 04, 2010; Online January 04, 2010

This paper aims to show how confocal microscopy can be useful for characterizing menisci in a flat plate heat pipe made of silicon. The capillary structure is made of radial microgrooves whose width decreases from the periphery to the center of the system. A transparent plate is used to close the system and allow visualizations. The confocal method allows measuring both the liquid film shape inside the grooves and the condensate films on the fins. The film thickness is lower than 10μm. The measurements show that the condensate film forms a drop connected to the meniscus in the grooves but their curvatures are reversed. As a result, a very thin region shall exist where the liquid formed by condensation is drained to the grooves. The drop curvature radius decreases from the condenser to the evaporator like the meniscus radius in the grooves. Therefore, a small part of the liquid is drained by the fins from the evaporator to the condenser. Furthermore, the condensate film covers a large part of the system and can also be in contact with the evaporator at high heat fluxes.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic confocal microscopy

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Figure 2

Schematic of the silicon FPHP

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Figure 3

Schematic of the FPHP test apparatus

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Figure 4

Wall temperature profile along the empty FPHP and the FPHP filled with methanol (Twork=30°C, fr=4.7%)

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Figure 5

Wall temperature profile along the empty FPHP and the FPHP filled with methanol (Twork=30°C)

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Figure 6

Thermal resistance versus the filling ratio (Twork=30°C, q=8.4 W/cm2)

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Figure 7

(a) Meniscus curvature radii measured inside the grooves by confocal microscopy (Twork=30°C, fr=4.7%, q=8.4 W/cm2) and (b) comparison between experimental measurements and fitted circles (Twork=30°C, fr=4.7%, q=8.4 W/cm2)

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Figure 8

Measured meniscus curvature radii along the FPHP for different heat fluxes (Twork=30°C, fr=4.7%)

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Figure 9

Measured meniscus curvature radii on the fins for different heat fluxes (Twork=30°C, fr=4.7%)

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Figure 10

Thin film thickness at the middle of the fins for different heat fluxes (Twork=30°C, fr=4.7%)

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Figure 11

Measured meniscus curvature radii along the FPHP for two heat fluxes (Twork=50°C, fr=13.4%)

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