Quantitative Visualization of Two-Phase Acoustic Streaming Emitted from Ultrasonic Scaler

This study experimentally investigated two-phase acoustic streaming and droplet properties of aerosols, which were generated by a dental ultrasonic scaler. The velocity field of acoustic streaming was measured using particle image velocimetry with the generated liquid droplets as tracers, and the shadowgraph technique was adopted to measure the droplet diameter. In the PIV measurement of the gas-liquid two-phase flow, the injection of oil smoke substantially suppressed the number of invalid vectors. The acoustic streaming of the ultrasonic scaler showed maximum velocity at a region away from the scaler tip, and the maximum velocity increased with an increase in the liquid flow rate. The droplets of the ultrasonic scaler were generated by capillary waves and had a diameter on the order of tens of micrometers. These droplets effectively enhanced the velocity of the acoustic streaming in the two-phase case compared to the single-phase case without the droplets.