On the influence of buoyancy on the surface tension driven flow around a bubble on a heated wall |
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Authors: | G Wozniak K Wozniak H Bergelt |
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Institution: | 1. TU Bergakademie Freiberg, Institut für Fluidmechanik und Fluidenergiemaschinen, Lehrstuhl für Experimentelle Mechanik, Lampadiusstr. 2, D-09596, Freiberg, Germany
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Abstract: | The surface tension driven flow in the liquid vicinity of gas bubbles on a heated solid wall has been investigated both, in
a reduced gravity environment aboard a sounding rocket, and in an earth-bound experiment. Both experiments deal with temperature
gradients within the liquid surrounding of a bubble which cause variations of the surface tension. These, in turn, lead to
a liquid flow around the bubble periphery termed thermocapillary or thermal Marangoni-convection. On Earth, this phenomenon
is widely masked by buoyancy. We therefore carried out an experiment under reduced gravitational acceleration. In order to
simultaneously observe and record the flow field and the temperature field liquid crystal tracers have been applied. These
particles offer the feature of selectively reflecting certain wavelengths of incident white light depending on the crystals
temperature. Although the bubble injection system did not perform nominally during the flight experiment, some interesting
flow characteristics could be observed. Comparison of results obtained in microgravity to data measured on Earth reveal that
due to the interaction of thermocapillarity and buoyancy a very compact vortex flow results on ground, while in microgravity
the influence on the surface tension driven flow penetrates much deeper into the bulk. This result is of special interest
regarding the production of materials in space.
Dedicated to Professor Dr. Julius Siekmann on the occasion of his 70th birthday
The work described herein was supported by the German space agency DARA (Deutsche Agentur für Raumfahrtangelegenheiten GmbH)
through DARA Grant 50 WM 9434. The authors thank the European Space Agency (ESA) for the opportunity to conduct the TEXUS
33 sounding rocket experiment. The flight hardware has been partly built by Daimler-Benz-Aerospace which is gratefully acknowledged.
Also, the authors are indebted to Mr. H.-H. Wolf for his careful evaluation of the particle images |
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