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Mixing and internal dynamics of droplets impacting and coalescing on a solid surface

Castrejon-Pita, J. R., Kubiak, Krzysztof, Castrejon-Pita, A. A., Wilson, M. C. T. and Hutchings, I. M. (2013) Mixing and internal dynamics of droplets impacting and coalescing on a solid surface. Physical Review B, 88. 023023. ISSN 1098-0121

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The coalescence and mixing of a sessile and an impacting liquid droplet on a solid surface are studied experimentally and numerically in terms of lateral separation and droplet speed. Two droplet generators are used to produce differently coloured droplets. Two high speed imaging systems are used to investigate the impact and coalescence of the droplets in colour from a side view with a simultaneous grey-scale view from below. Millimeter-sized droplets were used with dynamical conditions, based on the Reynolds and Weber numbers, relevant to microfluidics and commercial inkjet printing. Experimental measurements of advancing and receding static contact angles are used to calibrate a contact angle hysteresis model within a lattice Boltzmann framework, which is shown to capture the observed dynamics qualitatively and the final droplet configuration quantitatively. Our results show that no detectable mixing occurs during impact and coalescence of similar-sized droplets, but when the sessile droplet is sufficiently larger than the impacting droplet vortex ring generation can be observed. Finally we show how a gradient of wettability on the substrate can potentially enhance mixing.

Item Type: Article
Additional Information: This work was supported by the Engineering and Physical Sciences Research Council (Grant No. EP/H018913/1, Innovation in industrial inkjet technology) and the KACST-Cambridge Research Centre.
Uncontrolled Keywords: Droplets, Coalescence, Mixing, Lattice Boltzmann
Subjects: T Technology > TJ Mechanical engineering and machinery
Schools: School of Computing and Engineering
Depositing User: Krzysztof Kubiak
Date Deposited: 18 Sep 2014 15:34
Last Modified: 28 Aug 2021 18:56


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