Acoustic Cavitation Bubble Dynamics in Small Blind and Through Holes
* Presenting author
The interest in application of ultrasonic cavitation for cleaning and surface treatment processes is continuously growing. However, not much is known about the behavior of cavitation bubbles inside microstructural features of solid substrates. Here we report on experimental study of ultrasonically driven cavitation bubbles inside blind and through holes of PMMA plates by using high-speed imaging. Driving frequencies are around 38.5 kHz, and hole diameters range from 150 to 1000 micron. It is shown how wetting of the holes occurs via interior atomization caused by capillary waves. It is further seen that a large amount of the liquid volume inside the holes can be displaced within one acoustic cycle by the expansion of the cavitation bubbles. This reveals that ultrasonic cavitation is a very effective tool to intensify liquid exchange processes, and it can significantly improve micro-mixing in small structures. Examples of time resolved bubble oscillations in the holes are given which demonstrates the influence of the confined geometry.