An experimental study on the motion of water droplets in oil under ultrasonic irradiation

• The water droplet trajectory in oil under ultrasonic irradiation is described.
• The oscillation amplitude and frequency of water droplet motion are analyzed.
• The effect of major parameters on the motion of water droplet is studied.
• The critical intensity and optimum frequency of ultrasonic are obtained.

The motion of a single water droplet in oil under ultrasonic irradiation is investigated with high-speed photography in this paper. First, we described the trajectory of water droplet in oil under ultrasonic irradiation. Results indicate that in acoustic field the motion of water droplet subjected to intermittent positive and negative ultrasonic pressure shows obvious quasi-sinusoidal oscillation. Afterwards, the influence of major parameters on the motion characteristics of water droplet was studied, such as acoustic intensity, ultrasonic frequency, continuous phase viscosity, interfacial tension, and droplet diameter, etc. It is found that when the acoustic intensity and frequency are 4.89 W cm−2 and 20 kHz respectively, which are the critical conditions, the droplet varying from 250 to 300 μm in lower viscous oil has the largest oscillation amplitude and highest oscillation frequency.