Oscillations, Waves, and Interactions - GWDG

Acoustic cavitation 181
Figure 8. Continuously merging and splitting small cluster of bubbles close to a pressure
antinode (high-speed recording with one frame per driving period, i. e., 25000 fps; exposure
time 1 µs; frame size approximately 1 mm); from Ref. [10].
Figure 9. Large bubble at a 20.61 kHz sonotrode tip. The subsequent frames (top left
to bottom right) from a high-speed recording at 20000 fps (exposure time 20 µs, frame size
approx. 5 mm) show one picture per acoustic cycle. The bubble is roughly half-spherical
and strongly oscillating in a subharmonic (period-doubled) way. It is continuously shedding
microbubbles and exists much longer than the sequence shows.
Frequently, however, one encounters the cases (1a) and (3) from above, and the
bubble sizes are limited by the spherical shape stability threshold. This will be used
later for an upper estimate of the sizes of longer living bubbles.
3.3 Rectified diffusion
The mass and the species of non-condensable gas inside a bubble can change due
to diffusion through the bubble wall, i. e., from or into the liquid. Typically gases
have a finite solubility in liquids, and in dilute solutions at equilibrium, the gas