ARTICLE:

• CONVECTIVE INSTABILITIES IN EVAPORATING LIQUID LAYERS  download article

Nengli Zhang
Ohio Aerospace Institute at NASA Glenn Research Center, Cleveland, OH 44135, USA

David F. Chao
Fluid Physics and Transport Branch, NASA Glenn Research Center, Cleveland, OH 44135, USA

J. M. Sankovic
National Aeronautics and Space Administration, John H. Glenn Research Center, Cleveland, Ohio, U.S.A.

ABSTRACT

Based on an analysis of non-dimensionalized perturbation equations with relevant boundary conditions for an evaporating thin liquid layer, a generalized Marangoni number and a generalized Rayleigh number are derived to serve as the dimensionless control parameters. From these two generalized dimensionless numbers the traditional Rayleigh number derived from Rayleigh theory and the traditional Marangoni number derived from Pearson theory can be naturally obtained, respectively, when the evaporation rate vanishes and the corresponding boundary conditions are applied. Circulating flows in evaporating layers show a different pattern from that in the layers heated from below without evaporation. Evaporation is identified as a motivity to energize Rayleigh-Bénard convection and/or Marangoni-Bénard convection. The mechanisms for the convective instabilities in evaporating liquid layers are described from physical viewpoint in detail. The experimental results, showing that convective flows occur in evaporating liquid layers as long as evaporation is strong enough regardless of whether the layers are heated or cooled from below, convincingly prove the validity of the mechanism of evaporation-driven convective instability in evaporating liquid layers.

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MPH-18 pages

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