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International Heat Transfer Conference 16

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

EVAPORATION OF BINARY MIXTURES: POOLS AND DROPLETS

Adam G. L. Williams
Institute for Multiscale Thermofluids, School of Engineering, The University of Edinburgh, UK

Pedro J. Saenz
Department of Mathematics, MIT, USA

George Karapetsas
Chemical Engineering, University of Thessaloniki, Greece

Khellil Sefiane
The University of Edinburgh, James Clerk Maxwell Building, Kings Buildings, School of Engineering, Edinburgh EH9 3FB, United Kingdom; Tianjin Key Lab of Refrigeration Technology, Tianjin University of Commerce, 300134

Omar K. Matar
Department of Chemical Engineering, Imperial College London, Prince Consort Road, London SW7 2AZf

Prashant Valluri
Institute for Multiscale Thermofluids, School of Engineering, The University of Edinburgh, UK

DOI: 10.1615/IHTC16.bae.024179
pages 821-826


KEY WORDS: Boiling and evaporation, Numerical simulation and super-computing, Evaporation, Binary Mixture, Sessile Droplets, DNS, CFD, Lubrication Approximation, Stability Analysis

Abstract

Evaporation of a binary mixture pool or droplet is a highly dynamic and complex process with flow driven by the presence of thermal and solutal Marangoni stresses. Experiments on ethanol/water drops have identified chaotic regimes on both the surface and interior of the droplet, while mixture composition has also been seen to govern drop wettability. Using both DNS and lubrication-type approaches, we present models for the evaporation of a binary mixture liquid pool and an axisymmetric binary droplet deposited on a heated substrate. For both cases we assume liquid surface tension is linearly dependent on both temperature and concentration while mixture properties such as viscosity also vary locally with concentration. In the case of the pool we consider a rectangular domain with a horizontal temperature gradient and use DNS to solve the governing equations. The Volume-of-Fluid method is used to account for the deformable liquid-gas interface. Systems with low Prandtl number (Pr < 1) are focused on and we examine the solutal effects arising from the introduction of the second component. For the drop we consider a thin profile with a moving contact line, taking also into account the commonly ignored effects of inertia which drives interfacial instability. We derive evolution equations and explore the dimensionless parameter space to examine the resultant effects on drop wetting and evaporation where we find qualitative agreement with experiments in both these areas.

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