Cavitation occurs when vacuum pressure is lowered to the vapor pressure of the liquid, causing what phenomena?

• A. Gas bubbles form and persist.
• B. Vapor bubbles form and collapse.
• C. Air pockets prevent flow.
• D. Temperature of the liquid rises.

Answer: (B)

When pressure in the liquid drops below its vapor pressure, tiny regions of liquid vaporize and form vapor-filled bubbles. As the surrounding pressure rises or the bubbles move into a higher-pressure area, those vapor bubbles rapidly collapse or implode. This sequence—bubbles forming due to low pressure and then collapsing when pressure returns—is the defining behavior of cavitation and is what can cause shock waves and damage to equipment. The idea of gas bubbles forming and persisting isn’t the same phenomenon, since cavitation centers on vaporization under low pressure rather than dissolved gas coming out of solution. Air pockets aren’t the primary event Cavitation describes, and while the collapse can generate heat, temperature rise isn’t the fundamental phenomenon being described.