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Breakup and non-coalescence mechanism of aqueous droplets suspended in castor oil under electric field

Published online by Cambridge University Press:  19 September 2019

Subhankar Roy ,
Vikky Anand Open the ORCID record for Vikky Anand [Opens in a new window]  and
Rochish M. Thaokar Open the ORCID record for Rochish M. Thaokar [Opens in a new window]
Subhankar Roy
Affiliation:
Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
Vikky Anand
Affiliation:
Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
Rochish M. Thaokar*
Affiliation:
Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
*
†Email address for correspondence: rochish@che.iitb.ac.in
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Abstract

The effect of an electric field on the coalescence of two water droplets suspended in an insulating oil (castor oil) in the non-coalescence regime is investigated. Unlike the immediate breakup of the bridge, as reported in earlier studies, e.g. Ristenpart et al. (Nature, vol. 461 (7262), 2009, pp. 377–380), the non-coalescence observed in our experiments indicate that at strong fields the droplets exhibit a tendency to coalesce, the intervening bridge thickens whereafter the bridge dramatically begins to thin, initiating non-coalescence. Numerical simulations using the boundary integral method are able to explain the physical mechanism of thickening of this bridge followed by thinning and non-coalescence. The underlying reason is the competing meridional and azimuthal curvatures which affect the pressure inside the bridge to become either positive or negative under the effect of electric field induced Maxwell stresses. Velocity and pressure profiles confirm this hypothesis and we are able to predict this behaviour of transitory coalescence followed by non-coalescence.

JFM classification

Drops and Bubbles: Breakup/coalescence Drops and Bubbles: Drops Drops and Bubbles: Electrohydrodynamic effects
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 878 , 10 November 2019 , pp. 820 - 833
Copyright
© 2019 Cambridge University Press 

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