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ARTICLE

On the Dynamic Capillary Effects in the Wetting and evaporation process of Binary Droplets

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1 School of Engineering and Electronics, University of Edinburgh, Kings Buildings, Mayfield road, Edinburgh EH9 3JL, UK. Email:ksefiane@ed.ac.uk

Fluid Dynamics & Materials Processing 2005, 1(3), 267-276. https://doi.org/10.3970/fdmp.2005.001.267

Abstract

In this paper the experimental results on the wetting behaviour of volatile binary sessile drops are reported. The evaporation rate is varied through the control of the ambient total pressure. The dynamic wetting contact angle of an evaporating Water-Ethanol drop is investigated at various sub-atmospheric pressures. The wetting properties (contact angle, shape and volume) are monitored in time using a drop shape analysis instrument. The results show that the evaporation of the binary droplet takes place in two stages: the first stage where the wetting behaviour is very similar to the pure ethanol case and a second stage where the behaviour is very similar to the pure water case. The effect of varying the evaporation rate is found to shift the observed stages. The analysis of these results shows that it seems that in these conditions the evaporation proceeds such that in a first stage where mostly the more volatile component evaporates and a second stage where mostly the less volatile component evaporates. It appears however that during these evaporation stages there can be an evaporation of both components in different proportions. This is clearly influenced by the total evaporation rate and the diffusion from the bulk to the interface.

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