Introduction To Ultrasonic Cavitation

Ultrasonic cavitation refers to the dynamic process of growth and collapse of micro gas nucleus cavitation bubbles existing in liquids, which vibrate under the action of sound waves and occur when the sound pressure reaches a certain value. After three steps of cavitation bubble formation, growth, and severe collapse.
When a container filled with liquid is fed into an ultrasonic cleaner, tens of thousands of tiny bubbles, known as cavitation bubbles, are generated due to the vibration of the liquid. These bubbles grow in the negative pressure zone formed by the longitudinal propagation of ultrasound, and quickly close in the positive pressure zone, thus being compressed and stretched under alternating positive and negative pressures. At the moment when a bubble is compressed until it collapses, a huge instantaneous pressure is generated, typically reaching tens to hundreds of megapascals.
Suslick et al. measured that cavitation can increase the temperature of the gas-phase reaction zone to around 5200 K, the effective temperature of the liquid-phase reaction zone to around 1900 K, and the local pressure to around 5.5O5 × 10 kPa, with a temperature change rate of up to 10. K/s, accompanied by strong shock waves and micro jets with speeds of up to 400 km/h. This huge instantaneous pressure can cause rapid damage to the solid surface suspended in the liquid.
Ultrasonic cavitation is usually divided into two types: steady-state cavitation and transient cavitation:
Steady state cavitation refers to the cavitation bubbles generated at low sound intensity (generally less than 10 w/cm), whose size oscillates near its equilibrium size, generating cycles of several cycles. When it is expanded to make its resonance frequency equal to the frequency of sound waves, a high-energy coupling between the sound field and the bubble occurs, resulting in significant cavitation.
Transient cavitation refers to cavitation bubbles with a shorter lifespan (mostly occurring within one sound wave cycle) generated under the action of large sound intensity (generally greater than 1 W/cm).

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