Surface jets and internal mixing during the coalescence of impacting and sessile droplets

Sykes, Thomas C. and Castrejón-Pita, Alfonso A. and Castrejón-Pita, J. Rafael and Harbottle, David and Khatir, Zinedine and Thompson, Harvey M. and Wilson, Mark (2020) Surface jets and internal mixing during the coalescence of impacting and sessile droplets. Phys. Rev. Fluids, 5 (023602). ISSN 2469-990X

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Abstract

The internal dynamics during the coalescence of a sessile droplet and a subsequently deposited impacting droplet, with either identical or distinct surface tension, is studied experimentally in the regime where surface tension is dominant. Two color high-speed cameras are used to capture the rapid internal flows and associated mixing from both side and bottom views simultaneously by adding an inert dye to the impacting droplet. Given sufficient lateral separation between droplets of identical surface tension, a robust surface jet is identified on top of the coalesced droplet. Image processing shows this jet is the result of a surface flow caused by the impact inertia and an immobile contact line. By introducing surface tension differences between the coalescing droplets, the surface jet can be either enhanced or suppressed via a Marangoni flow. The influence of the initial droplet configuration and relative surface tension on the long-term dynamics and mixing efficiency, plus the implications for emerging applications such as reactive inkjet printing, are also considered.

Item Type: Article
Identification Number: https://doi.org/10.1103/PhysRevFluids.5.023602
Date: 24 February 2020
Uncontrolled Keywords: capillary waves; contact line dynamics; drop coalescence; drop interactions; surface tension effects
Subjects: F900 Others in Physical Sciences
H300 Mechanical Engineering
Divisions: Faculty of Computing, Engineering and the Built Environment > School of Engineering and the Built Environment
Faculty of Computing, Engineering and the Built Environment
Depositing User: Zinedine Khatir
Date Deposited: 28 May 2020 08:24
Last Modified: 28 May 2020 08:24
URI: http://www.open-access.bcu.ac.uk/id/eprint/9268

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