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Experiments on isothermal and non-isothermal spreading

Published online by Cambridge University Press:  26 April 2006

Peter Ehrhard
Peter Ehrhard
Affiliation:
Kernforschungszentrum Karlsruhe GmbH, Institut für Angewandte Thermo- und Fluiddynamik, Postfach 3640, D-76021 Karlsruhe, Germany
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Abstract

Experiments are performed on axisymmetric spreading of viscous drops on glass plates. Two liquids are investigated: silicone oil (M-100), which spreads to ‘infinity’, and paraffin oil, which spreads to a finite-radius steady state. The experiments with silicone oil partly recover the behaviour of previous workers’ data; those experiments with paraffin oil provide new data. It is found that gravitational forces dominate at long enough times while at shorter times capillary forces dominate. When the plate is heated or cooled with respect to the ambient gas, thermocapillary forces generate flows that alter the spreading dynamics. Heating (cooling) the plate is found to retard (augment) the spreading. Moreover, in case of partial wetting, the drop radius finally approached is smaller (larger) for a heated (cooled) plate. These data are all new. All these observations are in good quantitative agreement with the related model predictions of Ehrhard & Davis (1991). A breakdown of the axisymmetric character of the flow is observed only for very long times and/or very thin liquid layers.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 257 , December 1993 , pp. 463 - 483
Copyright
© 1993 Cambridge University Press

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