If a liquid is under pressure and above its atmospheric boiling point, a leak below the liquid level will result in what phenomenon?

• A. A stream of liquid flashing partially into vapor
• B. A stream of liquid remaining liquid
• C. A stream of vapor
• D. A jet of dry gas

Answer: (A)

When a liquid that’s under pressure is released into a region of lower pressure, it can evaporate rapidly if its temperature is above the boiling point at that lower pressure. In this case, the liquid is hotter than its atmospheric boiling point, so once it exits the leak into the surrounding environment, it can no longer remain entirely in the liquid phase. The sudden drop in pressure causes part of the liquid to flash into vapor while the rest stays liquid, producing a jet that contains both liquid and vapor. That’s why the stream is described as flashing partially into vapor.