How do dust particles and dissolved gases make cavitation more likely?

In the study of fluid mechanics, cavitation is the formation of vapor bubbles in a liquid when the pressure drops to the liquid's vapor pressure. While cavitation is often described as the formation of vapor, the presence of impurities such as dust particles and dissolved gases makes the process more likely to occur.

These substances act as nucleation sites within the fluid. When the pressure in a high-velocity region—such as a constriction in a pipe—falls, these particles and gas pockets provide a surface or a starting point for bubbles to form more easily than they would in a perfectly pure liquid. For instance, when water flows through a restricted opening, the pressure may drop significantly; the presence of dissolved gases assists the water in cavitating, leading to the formation and subsequent collapse of tiny bubbles as the fluid moves into higher-pressure regions. This phenomenon is responsible for the characteristic hissing or knocking sounds associated with cavitating flow.12