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Dynamics of drop coalescence at fluid interfaces

Published online by Cambridge University Press:  10 February 2009

FRANÇOIS BLANCHETTE  and
TERRY P. BIGIONI
FRANÇOIS BLANCHETTE*
Affiliation:
School of Natural Sciences, University of California Merced, 5200 N. Lake Road, Merced, CA 95343, USA
TERRY P. BIGIONI
Affiliation:
Department of Chemistry, University of Toledo, 2801 W. Bancroft Street, Toledo, OH 13606, USA
*
†Email address for correspondence: fblanchette@ucmerced.edu
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Abstract

Drop coalescence was studied using numerical simulations. Liquid drops were made to coalesce with a body of the same liquid, either a reservoir or a drop of different size, each with negligible impact velocity. We considered either gas or liquid as a surrounding fluid, and experimental results are discussed for the gas–liquid set-up. Under certain conditions, a drop will not fully coalesce with the liquid reservoir, leaving behind a daughter drop. Partial coalescence is observed for systems of low viscosity, characterized by a small Ohnesorge number, where capillary waves remain sufficiently vigourous to distort the drop significantly. For drops coalescing with a flat interface, we determine the critical Ohnesorge number as a function of Bond number, as well as density and viscosity ratios of the fluids. Studying the coalescence of two drops of different sizes reveals that partial coalescence may occur in low-viscosity systems provided the size ratio of the drops exceeds a certain threshold. We also determine the extent to which the process of partial coalescence is self-similar and find that the viscosity of the drop has a large effect on the droplet's vertical velocity after pinch off. Finally, we report on the formation of satellite droplets generated after a first pinch off and on the ejection of a jet of tiny droplets during coalescence of a parent drop significantly deformed by gravity.

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Papers
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Journal of Fluid Mechanics , Volume 620 , 10 February 2009 , pp. 333 - 352
Copyright
Copyright © Cambridge University Press 2009

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