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Breakup of a conducting drop in a uniform electric field

Published online by Cambridge University Press:  11 August 2014

Rahul B. Karyappa ,
Shivraj D. Deshmukh  and
Rochish M. Thaokar
Rahul B. Karyappa
Affiliation:
Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
Shivraj D. Deshmukh
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

A conducting drop suspended in a viscous dielectric and subjected to a uniform DC electric field deforms to a steady-state shape when the electric stress and the viscous stress balance. Beyond a critical electric capillary number $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{Ca}$, which is the ratio of the electric to the capillary stress, a drop undergoes breakup. Although the steady-state deformation is independent of the viscosity ratio $\lambda $ of the drop and the medium phase, the breakup itself is dependent upon $\lambda $ and $\mathit{Ca}$. We perform a detailed experimental and numerical analysis of the axisymmetric shape prior to breakup (ASPB), which explains that there are three different kinds of ASPB modes: the formation of lobes, pointed ends and non-pointed ends. The axisymmetric shapes undergo transformation into the non-axisymmetric shape at breakup (NASB) before disintegrating. It is found that the lobes, pointed ends and non-pointed ends observed in ASPB give way to NASB modes of charged lobes disintegration, regular jets (which can undergo a whipping instability) and open jets, respectively. A detailed experimental and numerical analysis of the ASPB modes is conducted that explains the origin of the experimentally observed NASB modes. Several interesting features are reported for each of the three axisymmetric and non-axisymmetric modes when a drop undergoes breakup.

JFM classification

Drops and Bubbles: Breakup/coalescence Drops and Bubbles: Drops Drops and Bubbles: Electrohydrodynamic effects
Type
Papers
Information
Journal of Fluid Mechanics , Volume 754 , 10 September 2014 , pp. 550 - 589
Copyright
© 2014 Cambridge University Press 

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Karyappa et al. supplementary movie

Breakup of a water drop suspended in castor oil (figure 10): (a, Ca, λ) = (112 μm, 0.40, 0.00126).

Download Karyappa et al. supplementary movie(Video)
Video 1.2 MB

Karyappa et al. supplementary movie

Regular jet breakup mode of a conducting drop for high viscosity ratio (figure 18(a)): (a, Ca, λ) = (190 μm , 0.30, 2.0).

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Video 1 MB

Karyappa et al. supplementary movie

Effect of electric capillary number Ca on the breakup mode (figure 19(a)): (a, Ca, λ) = (116 μm, 0.25, 0.575). At low Ca, a drop undergoes ASPB pointed ends breakup mode followed by NASB regular jet mode.

Download Karyappa et al. supplementary movie(Video)
Video 1.2 MB

Karyappa et al. supplementary movie

Effect of electric capillary number Ca on the breakup mode (figure 19(c)): (a, Ca, λ) = (105 μm, 1.1, 0.575). At high Ca, a drop undergoes ASPB pointed ends breakup mode followed by NASB open jet mode.

Download Karyappa et al. supplementary movie(Video)
Video 1.3 MB