The roles of acoustic cavitations in the ultrasonic cleansing of fouled micro-membranes

Abstract

This paper concerned the experimental studies on the cleansing mechanism of acoustic cavitation bubbles near the fouled micro-membranes. The existence of the membrane created asymmetry in the flow field, which forced the cavitation bubble to oscillate non-spherically and finally brought forth the jet impact. The oscillations and micro-jets of the cavitation bubbles enhanced the dynamic features of the fluid nearfield and improved the capability of removing fouling. The study on the acoustic multi-bubble system was quite complicated, so first, we focused on the individual bubble dynamics near the membrane. A succession of individual cavitation bubbles were created by Q-switched Nd: YAG laser pulses and observed using a high-speed camera (up to 100 000 frames per second). The jet flow hit against the membrane surface with velocity above 100 m/s, which was strong enough to remove the adherent fouling. We compared the cleansing effects of the cavitation bubbles with different laser energies and stand-off distances from the membrane surface. And then based on the individual bubble dynamics, we can deduce the influence of cavitations in the ultrasonic cleansing of micro-membranes.