Cavitation Bubble Dynamics in Sonicated Submerged Flow Tubes
* Präsentierender Autor
Zusammenfassung:Bubble dynamics and luminol emissions of cavitation in millimeter-sized PFA flow tubes, submerged in an ultrasonic bath reactor, are investigated for 25-27 kHz driving frequency. Nucleation of cavitation in the tubes only takes place via a free interface, realized here in form of a water-air slug flow. High-speed recordings show that cavitation bubbles in the water slugs frequently develop localized structures in form of clusters or bubble “plugs”. Bubbles in these structures undergo frequent collisions with adjacent bubbles, i.e. the free paths before merging or splitting events are short. Due to motion and mutual interaction, bubbles often collapse with a fast displacement, suggesting jetting dynamics. Bubble compression ratios are estimated on basis of observed individual bubble dynamics and numerical fitting by a single bubble model. The resulting conditions allow for dissociation of water vapor, which is in accordance with luminol emissions from active bubble zones in the tubes. Some peculiarities of bubble cluster dynamics and sonochemistry inside small flow tubes is discussed.