In a two-phase release, which quantity determines how much liquid flashes to vapor upon release?

• A. Vapor density
• B. Flash ratio
• C. Heat capacity
• D. Boiling point

Answer: (B)

Flashing during a two-phase release is governed by how much of the liquid can transform into vapor when the pressure drops. This amount is captured by the flash ratio, which describes the vapor mass fraction produced in the flashing process. A higher flash ratio means more liquid becomes vapor and the mixture becomes more vapor-dominated; a lower ratio means most of the liquid remains liquid.

Vapor density tells you how dense the resulting vapor is, not how much of it forms. Heat capacity relates to how much energy is needed to change temperature, not the fraction that flash-evaporates. Boiling point marks the temperature at which boiling begins at a given pressure, but it doesn't by itself quantify how much will flash when pressure is released.