The Importance of Control over Bubble Size Distribution in Pulsed Megasonic Cleaning

The presence of acoustic cavitation in the cleaning liquid is a crucial precondition for cleaning action. One can achieve enhanced cleaning by periodically switching the ultrasonic agitation on and off rather than sonicating the liquid in a continuous fashion. The physical effects leading to that improvement are investigated experimentally with a dedicated setup and correlated to cleaning results obtained in an experimental cleaning tank. With the first setup, sonoluminescence and cavitation noise are measured simultaneously while imaging the nucleation and the interaction of the bubbles with the sound field using Hi-Speed Stroboscopic Schlieren Imaging. In this way it is possible to identify the role of streamer bubbles and transient cavitation. Furthermore, the attenuation of the sound field due to the highly efficient bubble induced acoustic scattering and the growth of bubbles due to coalescence is investigated. The results give an idea of the stability of the bubble size distribution during and after the nucleation process. The measurements obtained for pulsed megasonic agitation are compared to that obtained while sonicating the liquid continuously. They are further correlated to experimental data on particle removal efficiency for varying pulse duration, and corresponding cavitation noise measurements. Here, the latter proves to be a suitable and easy-to-do method to identify cleaning regimes beforehand. © 2012 American Institute of Physics.status: publishe