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Open AccessArticle

Coalescence Dynamics of Acoustically Levitated Droplets

Department of Mechanical Engineering, Kogakuin University, Tokyo 163-8677, Japan
Graduate School of Systems and Information Engineering, University of Tsukuba, Tsukuba 305-8573, Japan
Faculty of Engineering, Information and Systems, University of Tsukuba, Tsukuba 305-8573, Japan
Author to whom correspondence should be addressed.
Micromachines 2020, 11(4), 343;
Received: 27 February 2020 / Revised: 22 March 2020 / Accepted: 24 March 2020 / Published: 26 March 2020
(This article belongs to the Special Issue Acoustofluidics)
The contactless coalescence of a droplet is of paramount importance for physical and industrial applications. This paper describes a coalescence method to be used mid-air via acoustic levitation using an ultrasonic phased array system. Acoustic levitation using ultrasonic phased arrays provides promising lab-on-a-drop applications, such as transportation, coalescence, mixing, separation, evaporation, and extraction in a continuous operation. The mechanism of droplet coalescence in mid-air may be better understood by experimentally and numerically exploring the droplet dynamics immediately before the coalescence. In this study, water droplets were experimentally levitated, transported, and coalesced by controlled acoustic fields. We observed that the edges of droplets deformed and attracted each other immediately before the coalescence. Through image processing, the radii of curvature of the droplets were quantified and the pressure difference between the inside and outside a droplet was simulated to obtain the pressure and velocity information on the droplet’s surface. The results revealed that the sound pressure acting on the droplet clearly decreased before the impact of the droplets. This pressure on the droplets was quantitatively analyzed from the experimental data. Our experimental and numerical results provide deeper physical insights into contactless droplet manipulation for futuristic lab-on-a-drop applications. View Full-Text
Keywords: acoustic levitation; ultrasonic phased array; droplet; coalescence; lab-on-a-drop acoustic levitation; ultrasonic phased array; droplet; coalescence; lab-on-a-drop
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MDPI and ACS Style

Hasegawa, K.; Watanabe, A.; Kaneko, A.; Abe, Y. Coalescence Dynamics of Acoustically Levitated Droplets. Micromachines 2020, 11, 343.

AMA Style

Hasegawa K, Watanabe A, Kaneko A, Abe Y. Coalescence Dynamics of Acoustically Levitated Droplets. Micromachines. 2020; 11(4):343.

Chicago/Turabian Style

Hasegawa, Koji; Watanabe, Ayumu; Kaneko, Akiko; Abe, Yutaka. 2020. "Coalescence Dynamics of Acoustically Levitated Droplets" Micromachines 11, no. 4: 343.

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