High Power Ultrasound Cavitation

High Power Ultrasound Cavitation

Ultrasound is sound beyond acoustic sound (i.e. from 20 kHz to the megahertz range). In aqueous media, ultrasound waves cause periodic compression (pressure) and expansion (tension, negative pressure) of the medium treated with ultrasound. In the negative pressure range, high-intensity ultrasound leads to expansion of the aqueous phase, which leads to the formation of microscopic voids in the liquid. These bubbles fill with steam or gas. They grow in tension phases and shrink in pressure phases until they implode. This event is referred to as cavitation, a process under extreme (adiabatic) conditions. In the frequency range from 20–100 kHz particularly large cavitation bubbles are generated; these cause extreme mechanical shear forces during collapse. This results in pressures of 500 bar and a temperature of 5,000 °C on a micro-scale. These ultrasonic forces are capable of destroying any surface, no matter how robust it is.