cavitaation

Cavitation is the formation, growth, and implosive collapse of vapor-filled cavities in a liquid that occurs when local pressure falls below the liquid’s vapor pressure. Nucleation typically begins at microscopic crevices, impurities, or dissolved gases; as pressure fluctuates in flowing or insonated liquids, small bubbles can form, grow, and intermittently persist.

There are two main forms: inertial (transient) cavitation, in which bubbles rapidly expand and violently collapse, and non-inertial (gas-filled or stable) cavitation, in which bubbles oscillate with pressure without a violent collapse. Inertial cavitation generates shock waves, microjets, and extreme but localized temperatures and pressures, which can damage materials or alter chemical processes.

Cavitation occurs in many fluid systems, including ship propellers, pumps, turbines, valves, and nozzles, especially under high flow or abrupt pressure drops. It also arises in ultrasonic cleaning, sonochemistry, and medical uses such as high-intensity focused ultrasound and lithotripsy. While often deleterious, controlled cavitation can aid cleaning and certain therapies.

Mitigation and control rely on avoiding low-pressure regions, reducing the amount of dissolved gas, degassing liquids, improving flow conditioning, and adjusting operating conditions. Design strategies include smoother geometries, surface coatings, maintaining adequate static pressure, and using anti-cavitation devices.

Modeling cavitation employs bubble dynamics equations such as the Rayleigh–Plesset model, often extended to multiple bubbles, and depends on fluid properties, temperature, and dissolved gas content. Detection methods include high-speed imaging, acoustic emission monitoring, and pressure sensing.