Cavitation

In ultrasonic cleaning devices, cavitation promotes the removal of dirt particles from the solid cleaning object. Other applications are homogenisation, in which emulsions are produced, and the degassing of liquids. Due to the very low pressure within the cavitation bubbles, gases dissolved in the medium are transformed into a gaseous state. When the cavitation bubbles implode, they are then only reabsorbed by the medium up to the point of solution equilibrium. The excess gas escapes from the medium. The effect used for the sonication of e.g. biogas substrate uses the shear forces generated by cavitation at the solid-liquid interface and the resulting attack of the surface, which leads to a disintegration and disintegration of coherent particles in liquid media. 

The proof of this cavitation effect can be easily obtained with the so-called Foil test yield: An aluminium foil of 0.01 to 0.02 mm thickness is stretched on a wire frame, placed in the liquid and sonicated for 60 seconds. The cavitation causes perforations in the foil, from which the intensity and distribution of the cavitation can be easily seen.