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Research Papers: Experimental Techniques

Imaging of Surface-Tension-Driven Convection Using Liquid Crystal Thermography

[+] Author and Article Information
T. W. Dutton1

Department of Mechanical Engineering, University of Houston, Engineering Building One, Houston, TX 77204

L. R. Pate2

Department of Mechanical Engineering, University of Houston, Engineering Building One, Houston, TX 77204

D. K. Hollingsworth3

Department of Mechanical Engineering, University of Houston, Engineering Building One, Houston, TX 77204hollingsworth@uh.edu

1

Present address: Associated Equipment Company, Pearland, TX.

2

Present address: NASA Johnson Space Center, Houston, TX.

3

Corresponding author.

J. Heat Transfer 132(12), 121601 (Sep 20, 2010) (6 pages) doi:10.1115/1.4002114 History: Received September 26, 2009; Revised June 27, 2010; Published September 20, 2010; Online September 20, 2010

Surface-tension forces can drive fluid motion within thin liquid layers with a free surface. Spatial variations in the temperature of the free surface create surface tractions that drive cellular motions. The cells are most commonly hexagonal in shape and they scale on the thickness of the fluid layer. This investigation documents the formation of cells in the liquid film in the presence of a uniform-heat-flux lower boundary condition. Liquid crystal thermography was used to image the cells and measure the temperature distribution on the lower surface of the liquid layer. A 1.1 mm deep pool of silicone oil was supported on a 50μm thick electrically heated metal foil. The oil was retained inside an independently heated acrylic ring mounted on the top surface of the foil and a dry-ice cooling plate served as the low-temperature sink above the free surface of the oil. Color images of hexagonal convection cells were captured using liquid crystal thermography and a digital image acquisition and processing system. The temperature distribution inside a typical cell was measured using thermographic image analysis. Experimental issues, such as the use of an independently heated retaining ring to control the height of the liquid film and the utility of a flux-based Marangoni number are discussed.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of cellular flow pattern (12)

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Figure 2

Diagram of fluid layers with upper and lower boundaries

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Figure 3

Drawings of apparatus: (a) overhead view and (b) side view (11)

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Figure 4

Typical liquid crystal image of the heated surface beneath the liquid layer

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Figure 5

Typical liquid crystal image of the center of the heated surface beneath the liquid layer

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Figure 6

Measured temperature distribution on the heated surface beneath the liquid layer

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Figure 7

Contour map of the temperature distribution in the neighborhood of one cell. Hexagon was added to indicate cell structure.

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