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Air entrapment of a neutral drop impacting onto a flat solid surface in electric fields

Published online by Cambridge University Press:  04 August 2022

Yu Tian
Affiliation:
State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
Yanchu Liu
Affiliation:
Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen 518055, China
Zihan Peng
Affiliation:
State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
Chenghao Xu
Affiliation:
Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen 518055, China
Dong Ye
Affiliation:
State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
Yin Guan
Affiliation:
School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Xinping Zhou
Affiliation:
State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Weiwei Deng*
Affiliation:
Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen 518055, China
YongAn Huang*
Affiliation:
State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
*
Email addresses for correspondence: yahuang@hust.edu.cn, dengww@sustech.edu.cn
Email addresses for correspondence: yahuang@hust.edu.cn, dengww@sustech.edu.cn

Abstract

When a charge neutral drop impacts on a flat solid substrate, a small air bubble is always trapped underneath due to the lubrication pressure coming from the viscous stress in the squeezed air film. Herein we find experimentally and numerically that the process of the air entrapment and the initial contact state of the drop with the substrate can be profoundly altered via an external electric field. In an electric field, the induced electric stresses at the bottom of the drop increase drastically right before the drop contacts the substrate, which acts against the lubrication pressure, resulting in reduced initial contact radius and air bubble size. When the external electric field reaches a critical value, the electrical stress accelerates the flow near the bottom of the drop and generates a conical tip quickly instead of a dimple, resulting in a centre contact and eliminating the air bubble entrapment. Based on the dipole mirror charge model, we find the dimensionless strength of critical electric field scales with the square root of capillary number based on the air viscosity. This scaling law of the critical electric field for eliminating the air bubble entrapment is verified experimentally and numerically. This work may offer a new way to mitigate defects caused by air bubble entrapment for inkjet printing and droplet-based additive manufacturing.

Information

Type
JFM Papers
Copyright
© The Author(s), 2022. Published by Cambridge University Press

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