Effects of micro bubbles vibration for increase of acoustic streaming

Abstract

The effects of the existence of micro bubbles in water for the increasing of acoustic streaming velocity are experimentally discussed. Velocity of acoustic streaming is observed on the sound axis by LDV (laser Doppler velocimeter). Acoustic streaming is generated by continuous ultrasonic sound transmitted by some PZT transducers whose diameter is 15 mm and resonant frequencies are 2.98 or 3.46 MHz. Sound pressures of ultrasonic sound are set to 80, 160, and 240 kPa at the last peak position on the sound axis. Micro bubbles are generated by extracting water with a syringe mechanism, decreasing the pressure of water down to 6.4% below static pressure. Average radius of micro bubbles is approximately 220 μm. The experimental results clearly show the velocity of acoustic streaming increases; the velocity increases from 9 to 13.5 mm/s when the micro bubbles exist. The harmonics are observed when the micro bubbles are generated. The mechanism for the increase of acoustic streaming is discussed from the point of view of the nonlinear effect of the bubble vibration.