Migration and Boiling of a Single Droplet in a Square Capillary Tube
Date Issued
2015
Date
2015
Author(s)
Ouyang, Jhen
Abstract
In this work, we study the migration and boiling of a single droplet in a heatedsquare capillary tube. Three different fluid combinations are used: n-pentane droplet in glycerol, Novec 7100 droplet in glycerol and ethanol water mixture of different mass fraction (w = 0, 0.1, 0.5, 0.7, 0.9 and 1) in silicone oil. The wall temperature varies from 80°C to 120°C and nondimensional droplet ratios are tested: D/L = 0.3, 0.5 and 0.7. When the square capillary tube is heated, temperature gradient perpendicular to the tube axis is formed and the thermal capillary effect is induced so that the droplet experiences unbalanced force and starts to move toward the heated surface. As the wall temperature increase, the droplet begins to boil. The limit of superheat of the droplet can be observed when the surface tension of the droplet liquid is greater than the host liquid. From the results, the drift velocity increase with the increase of ethanol quality and the wall temperature. In addition, the droplet accelerates as it moves toward to the heated wall. This may ascribed to the rapid rise of temperature gradient near the heated wall. We also find that larger droplet has a higher initial velocity, while smaller droplet speeds up eventually. Nevertheless, the droplet does not move or even drift to the cold wall at a mass fraction of 0.5. For droplet composed of ethanol/water mixture, no superheat limits observed. On the other hand, explosive boiling occurs for droplets of n-pentane and Novec 7100. The limit of superheat is affected by fluid properties and is independent of droplet size or tube dimension.
Subjects
capillary tube
droplet
migration
thermal capillary effect
limit of superheat
Type
thesis
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