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Electrohydrodynamic-induced partial coalescence between a droplet and a liquid–air interface

Published online by Cambridge University Press:  22 May 2023

Hao Chen ,
Wei Chen ,
Zhouping Yin  and
Haisheng Fang Open the ORCID record for Haisheng Fang [Opens in a new window]
Hao Chen
Affiliation:
School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China
Wei Chen
Affiliation:
State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China
Zhouping Yin*
Affiliation:
State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China
Haisheng Fang*
Affiliation:
School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China
*
† Email addresses for correspondence: hafang@hust.edu.cn, yinzhp@hust.edu.cn
† Email addresses for correspondence: hafang@hust.edu.cn, yinzhp@hust.edu.cn
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Abstract

When a droplet coalesces with a flat liquid–air interface, a secondary drop may be left behind resulting in only a partial coalescence rather than complete coalescence. In this paper, we employ an arbitrary Lagrangian–Eulerian method to demonstrate that applying an electric field favours the occurrence of partial coalescence. To understand this phenomenon, we systematically study the effect of an external electric field on the coalescence process between a droplet and a liquid–air interface. In an electric field, the induced electric stresses can overcome the downward flow of the droplet, thus lifting it upwards. As a result, the positive Laplace pressure in the neck region squeezes the droplet towards pinch-off. We observe that both the initial neck expansion and neck shrinkage are suppressed by the electric field. These effects become weaker as the Ohnesorge number $Oh$ increases. Based on the scaling analysis, we report a critical Ohnesorge number $O{h_c} = 14.39{\varGamma ^{3/2}} + 0.029$ to quantify the transition from partial coalescence to complete coalescence in the presence of an electric field, where $\varGamma $ represents the dimensionless electric Bond number. Finally, a relationship between the secondary droplet size and the two key dimensionless numbers of $Oh$ and $\varGamma $ has been developed, which could be useful for producing droplets of desired sizes in microfluidic applications.

JFM classification

Drops and Bubbles: Breakup/coalescence Drops and Bubbles: Electrohydrodynamic effects
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 963 , 25 May 2023 , A39
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Copyright
© The Author(s), 2023. Published by Cambridge University Press

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