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.

中文翻译：

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声悬浮液滴的聚结动力学。

液滴的非接触式聚结对于物理和工业应用至关重要。本文介绍了一种使用超声相控阵系统通过声悬浮在空中进行融合的方法。使用超声相控阵的声悬浮技术提供了有希望的点滴实验室应用，例如连续操作中的运输，聚结，混合，分离，蒸发和提取。通过在刚聚结之前通过实验和数值研究液滴动力学，可以更好地了解空中的液滴聚结机理。在这项研究中，通过受控的声场对水滴进行了实验性的悬浮，运输和聚结。我们观察到，液滴的边缘在聚结之前立即变形并相互吸引。通过图像处理，对液滴的曲率半径进行量化，并模拟液滴内部与外部之间的压力差，以获得液滴表面上的压力和速度信息。结果表明，作用在液滴上的声压在液滴撞击之前明显降低。从实验数据定量分析了液滴上的压力。我们的实验和数值结果为用于未来实验室的液滴应用中的非接触式液滴处理提供了更深入的物理见解。结果表明，作用在液滴上的声压在液滴撞击之前明显降低。从实验数据定量分析了液滴上的压力。我们的实验和数值结果为用于未来实验室的液滴应用中的非接触式液滴处理提供了更深入的物理见解。结果表明，作用在液滴上的声压在液滴撞击之前明显降低。从实验数据定量分析了液滴上的压力。我们的实验和数值结果为用于未来实验室的液滴应用中的非接触式液滴处理提供了更深入的物理见解。