Cavitating

Cavitating refers to the formation, growth, and collapse of vapor bubbles in a liquid caused by local reductions in pressure below the liquid’s vapor pressure or by rapid temperature changes. The process is most commonly observed in engineering fluids such as water, oil, or refrigerants, and it is a key concern for pumps, propellers, and hydraulic machinery. When pressure drops as the fluid accelerates around a surface or through a restriction, a zone of low pressure can develop. If the pressure falls sufficiently, the liquid partially vaporizes, creating microscopic cavities or bubbles. These cavities travel with the fluid flow until they encounter areas of higher pressure; the rapid compression of the vapor inside the bubble produces a violent collapse, generating intense local pressure spikes and high‑frequency acoustic waves.

The collapse of cavitation bubbles can erode metal and plastic components, reduce hydraulic efficiency, and generate noise or vibration. In marine propellers, cavitation may form on the blades, damaging the surface and diminishing thrust. In pumps, it can manifest as a drop in head, increased vibration, and eventual bearing wear. Cryogenic systems can experience “cryogenic cavitation,” where liquid nitrogen or helium forms vapor pockets under rapid depressurization.

Methods to mitigate cavitation include designing geometries to reduce pressure gradients, maintaining operating pressures above critical thresholds, adding anti‑cavitation fins or bubble‑forming elements, or using fluids with higher vapor pressures. Monitoring techniques such as acoustic sensors, vibration analysis, and pressure measurement help detect early signs of cavitation. Though often undesirable, controlled cavitation is used in certain cleaning, sonochemical, and ultrasonic applications, where the bubble collapse promotes mechanical cleaning or chemical reactions.