  Ultrasonic cavitation is the formation of vapour cavities within a liquid due
to the action of an ultrasound source. It is widely used for homogenization,
dispersion, deagglomeration, erosion, cleaning, milling, emulsification,
extraction, disintegration and sonochemistry. On the other hand, the so-called
cavitation number is used to assess the likelihood of cavitation in fluid flows
within a conduit or around a hydrofoil but it is not valid in ultrasonic
cavitation since there is no fluid flow. A recently formulated number predicts
the cavitation in case of sudden accelerations. The tip surface of an
ultrasonic probe is subjected to a continuous repetition of alternating
accelerations at high frequency. Therefore, the use of the recently formulated
number in ultrasonic cavitation is explored here. Simulations of the ultrasonic
probe in water just at the condition of cavitation onset have been performed
for a combination of probe diameters from 0.2 to 100 mm and frequencies 20, 30,
40, 100 and 1000 KHz. The recently formulated number is applied to these
combinations and it is found that can be used to predict ultrasonic cavitation.
Consequently, the dimensionless number can be used to decide the conditions to
avoid or generate cavitation when a fluid is sonicated and to increase
reproducibility in such conditions.
