Effect of Dual Frequency Ultrasound on the Bubble Formation in a Capillary Tube

A visual experimental was conducted to determine the effect of dual frequency ultrasound on the bubble formation and growth in a capillary quartz tube. The ultrasonic sound was applied to the heating section of a capillary tube by using electrically-controlled piezoelectric ceramics made of Pb-based lanthanum-doped zirconate titanates (PLZTs). The bubble formation and growth were recorded by a high speed camera. Experimental results show that the bubble formation and growth depend on PLZT frequency. When a dual frequency ultrasound (154 kHz and 474 kHz) was used, the nucleation sites for bubble formation were significantly increased and the bubble growth rate enhanced.