Flow structure and evaporation behavior of an acoustically levitated droplet

Kobayashi, Kenji; Goda, Atsushi; Hasegawa, Koji; Abe, Yutaka

doi:10.1063/1.5037728

Cited by 36 publications

(16 citation statements)

References 46 publications

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“…Furthermore, Hasegawa et al studied the interaction between the evaporation behavior of levitated droplets and their internal as well as external flow structures [4]. Kobayashi et al showed that there is a correlation between the internal as well as external flow structures in a levitated droplet and vapor concentration [28]. In addition, Bänsch et al studied the temperature, vapor concentration, and flow structure of levitated droplets via numerical simulation [29].…”

Section: Introductionmentioning

confidence: 99%

Evaporation of droplet in mid-air: Pure and binary droplets in single-axis acoustic levitator

Niimura

Hasegawa

2019

PLoS ONE

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Acoustic levitation method (ALM) is a container-less processing method with applications in various fields, including material processing, biology, and analytical chemistry. Because it is a container-less processing technique, ALM could prevent nucleation and contamination of materials being processed via contact with a container wall. It is well-known that evaporation of a sample is an important process in container-less processing of materials; however, the mechanism of evaporation in multicomponent droplets in a single acoustic levitator is still unclear. Thus, we evaluate and understand the evaporation of an acoustically levitated multicomponent droplet and manipulate the evaporation process of the sample in this study. Specifically, we investigate the evaporation process of pure and multicomponent droplets using container-less processing experimentally. The evaporation processes and temporal evolution of the surface temperature of a multicomponent droplet were evaluated using a high-speed camera and radiation thermometer, respectively. We used water, ethanol, methanol, hexane, acetone, pentane, and binary solutions (solution of 25 wt%, 50 wt%, and 75 wt% ethanol, methanol, and acetone, respectively) as test samples to study the effect of saturated vapor pressure on evaporation. Ethanol, methanol, and acetone droplets evaporate in two different stages. It was observed that the water vapor in the air condensed during the evaporation process of these water-soluble droplets; hence, our experimental data did not agree with the theoretical prediction in accordance with the d 2 law. Nevertheless, the evaporation behavior in the first stage of evaporation was consistent with the theoretical prediction. Furthermore, for binary droplets, as the concentration of the resultant solution increased owing to evaporation, the transition time from the first to the second stage of evaporation also increased. Based on these observations, estimation equations for binary droplets were developed to ensure that the experimental and theoretical values were in good agreement.

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Section: Introductionmentioning

confidence: 99%

Evaporation of droplet in mid-air: Pure and binary droplets in single-axis acoustic levitator

Niimura

Hasegawa

2019

PLoS ONE

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“…Although contactless droplet manipulation in mid-air is vital for future lab-on-a-drop applications, the nonlinear effect of strong acoustic fields in acoustic levitation, such as interfacial instability [15,16] and its transport phenomena [17][18][19][20][21][22][23] have been partially understood to date. The dissemination of droplet manipulation in acoustic levitation using an ultrasonic phased array system requires the fundamental physics of a levitated droplet to be fully understood.…”

Section: Ofmentioning

confidence: 99%

Coalescence Dynamics of Acoustically Levitated Droplets

et al. 2020

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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.

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“…These fields are used for calculating the acoustic radiation pressure exerted at each point of the drop surface, and then, the equilibrium shape of a droplet is determined by balancing the acoustic radiation pressure with the hydrostatic and capillary pressures using the Young-Laplace equation. To simplify the analysis, we assume an inviscid fluid and we neglect acoustic streaming 37,[58][59][60] and the generation of harmonics of the fundamental frequency. 61,62 A. Acoustic radiation pressure on the levitating drop…”

Section: Numerical Modelmentioning

confidence: 99%

“…34 Acoustic levitation can also be applied for measuring the surface tension of liquid drops 35,36 and for studying the evaporation of liquids. 37,38 In general, acoustic levitation is an important contactless manipulation method for the transportation and merging of liquid substances in midair. 14,39,40 Reliable methods for acoustically manipulating drops require a good understanding of the stability of levitating drops under the high intensity acoustic fields employed for levitation.…”

Section: Introductionmentioning

confidence: 99%