Which description applies to a liquid at a temperature lower than its saturation temperature?

• A. Saturation
• B. Boiling
• C. Subcooling
• D. Superheating

Answer: (C)

Subcooling means a liquid is cooled below its saturation temperature for the given pressure. In this state the liquid stays fully in the liquid phase and won’t vaporize until it absorbs enough heat to reach the saturation temperature. If a liquid were at the saturation temperature, it would be at the boiling point for that pressure and could begin to boil; boiling is the actual transition to vapor. Superheating would place the liquid above the saturation temperature, where it would be warmer than the boiling point and could vaporize more readily. Since the condition described is a temperature lower than the saturation temperature, subcooling is the correct description.