A better understanding on the transport phenomena, momentum (flow), heat, and mass transfer of acoustically levitated droplets is very important for several scientific and industrial fields. The flow generated by a nonlinear acoustic field is known as acoustic streaming. In acoustic levitation, multiscale acoustic streaming can be induced both inside and outside the droplet. In the internal flow field, the streaming configuration is affected by the physical properties of the droplet. The external flow field can be characterized by the applied sound pressure, physical properties of the droplet, and surrounding gas. These flow fields are instrumental in the heat and mass transfer of the levitated droplet. This review provides a recent advancement on the flow fields, heat, and mass transfer enhancement of the acoustically levitated droplet.

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Understanding liquid structures provides crucial information for uncovering the nature of glass transition. We adopted a combination of the aerodynamic levitation technique and the synchrotron hard X-rays to reveal the structure of high-temperature liquid oxides. To achieve accurate diffraction measurements, the two-axis diffractometer at the high-energy X-ray diffraction beamline BL04B2 of SPring-8 was upgraded. By installing four CdTe detectors and three Ge detectors, we can measure diffraction signals from levitated liquids approximately three times faster than the previous set-up. We have measured liquid (l)-Y2O3, l-Gd2O3 and l-Ho2O3. No first sharp diffraction peak (FSDP) was observed in these non-glass forming liquids but a sharp principal peak (PP) was observed. Density data on these liquids necessary for further analysis are currently measured using the electrostatic levitation furnace in the International Space Station (ISS).

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We aim to conduct the feasibility study for the contactless droplet transportation via an ultrasonic phased array system. Developed ultrasonic phased array system enables us to successfully levitate the 2 cSt silicone oil droplets in mid-air. The sound pressure field was simulated and the simulation results well predicted the sound pressure fields. Hereafter, the transportation of droplets was carried out by varying the speed of the focal point of sound. For lower transportation speeds of 50, 80, and 160 mm/s, the droplets were successfully transported due to the balance between the inertia force and the restoring force by the pressure gradient generated with sound pressure field acting on the droplets. Our experimental results demonstrated the contactless droplet transportation by the ultrasonic phased array system.

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The impact of liquid drops with dry and wetted solid surfaces has numerous applications in both natural and engineered systems. These applications include but not limited to the cooling of electronic components, spray drying, and tissue engineering. Even though there are many research studies in drop impact area, earlier studies had largely ignored the effect of Froude number variation on single drop and spray research. However, Dinc and Gray showed that while the evolution of the craters was generally similar, the time scale and the height of the Worthington jet were strongly influenced as the value of gravity increased. Medam et al. confirmed these results with their preliminary analysis. This paper consists of major outcomes such as how the impact time scales and crater radiuses varying with gravity and buoyancy. This study includes simulations of a spherical water drop impacting an upward facing wetted surface for a case in which the flow is known to remain axisymmetric (Reynolds number = 6690, Weber number = 139, layer depth/drop diameter = 0.837, and contact angle = 0°) for different gravity and buoyancy conditions (different drop and layer temperature) based on some of the planets and asteroids in our Solar System. Varying the gravity level changes the Froude number from 1.83 to infinity. It is obtained that gravity significantly affects the impact dynamics and time scales whereas buoyancy does not significantly alter results at least based on the dimensional numbers considered in this study. Drop and layer buoyancy effects on liquid distribution are not substantial at early simulation times and become more significant at later times.

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