What Cavitation is?
Cavitation effect ( regardless of what technology/method induced cavitation )
Cavitation ( from cavitas – vacuum ) is the process of forming cavities in a liquid – i.e. small liquid-free zones ("bubbles" or "voids") which occur when a volume of liquid is subjected to the rapid drop of pressure below the threshold value which is specific for each liquid, under particular conditions.
Liquid evaporates into the cavity from the surrounding medium; thus, the cavity is not a perfect vacuum but has a relatively low gas pressure.
Dissolved in liquid gasses migrate from liquid to the areas of low pressure in cavities.
When subjected to higher pressure, the liquid vapors condense, that causes voids rapid implosion, a release of condensation latent heat which cannot dissipate rapidly in the liquid.
Fast bubble collapse and heat release in very small volume cause releasing large magnitude of energy in different forms: temperature, pressure pulses, and oscillations, electrical effects, chemical effects, liquid microjet formation.
All these effects are local - high temperature (of the order of 1000 to 5000K), high pressure (100 to 5000 bar) while overall liquid medium remains at ambient conditions.
Cavitation – desirable and undesirable
Cavitation is usually a mostly unintended and undesirable phenomenon, causing damages ( in
pumps, propellers, etc.) and noise ( warships propellers’ noise).
Useful/desirable Cavitation :
- Ultrasound cleaning of surfaces, incl. semiconductors
- Ultrasound / sonochemical processes
- Mixing and dispersing
Inertial and Non-Inertial Cavitation
Non – Inertial Cavitation
Non-inertial cavitation is the process in which small bubbles
in a liquid are forced to oscillate in the presence of an acoustic
field, when the intensity of the acoustic field is insufficient to
cause total bubble collapse.
The phenomenon of flowing liquid rupture and formation of
cavity under the action of a sudden drop of pressure below the
threshold level is cavitation inception.
This phenomenon can occur when liquid flows around solid
body, or as a result of cavitating body fast movement in the
liquid ( propeller).