Improved ultrasonic cleaning of membranes with tandem frequency excitation

▸ Ultrasonic cleaning is caused by oscillating bubbles near to the membrane surface. ▸ Small bubbles can be formed on the membrane surface using a high-frequency ultrasound. ▸ A quick switch to a low-frequency ultrasound converts these bubbles into cleaning bubbles. ▸ This tandem frequency ultrasound field is studied in detail with high-speed photography. ▸ The trans-membrane pressure of the clean membrane is recovered.