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Coalescence and break-up of nearly inviscid conical droplets

Published online by Cambridge University Press:  17 December 2014

Casey T. Bartlett ,
Guillaume A. Généro  and
James C. Bird
Casey T. Bartlett
Affiliation:
Department of Mechanical Engineering, Boston University, Boston, MA 02215, USA
Guillaume A. Généro
Affiliation:
Department of Mechanical Engineering, Boston University, Boston, MA 02215, USA École Polytechnique, Route de Saclay, 91128 Palaiseau, France
James C. Bird*
Affiliation:
Department of Mechanical Engineering, Boston University, Boston, MA 02215, USA
*
†Email address for correspondence: jbird@bu.edu
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Abstract

In the presence of electric fields, pairs of liquid drops can be rapidly drawn together such that, at contact, the deformed interface resembles a double-cone. Following contact, these drop pairs are observed to either coalesce or recoil. Experimental and theoretical results suggest that the transition between coalescence and recoil is due to the conical drop topology rather than charge effects. However, even with this assumption, existing models disagree on how the transition develops, leading to different predictions of the critical cone angle and bridge morphology. Here we use high-resolution numerical simulations to highlight the impact of the initial double-cone angle on drop coalescence and reconcile the differences in the previous models. The results demonstrate a self-similar behaviour at intermediate scales for both coalescence and recoil that is independent of the other length scales in the problem. We calculate a critical polar angle of ${\it\theta}_{c}=1.14$ rad ($65.3^{\circ }$), or a complementary angle of ${\it\beta}=90^{\circ }-{\it\theta}_{c}=25^{\circ }$. This calculated critical angle for morphological transition is in agreement with previous experimental observations of ${\it\beta}\approx 27\pm 2^{\circ }$.

JFM classification

Drops and Bubbles: Breakup/coalescence Drops and Bubbles: Drops and Bubbles Interfacial Flows (free surface): Liquid bridges
Type
Papers
Information
Journal of Fluid Mechanics , Volume 763 , 25 January 2015 , pp. 369 - 385
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Copyright
© 2014 Cambridge University Press 

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