In the flashing liquid model, which statement describes the mass flow rate parameter Qm?

• A. Mass flow rate of the liquid
• B. Mass flow rate of the vapor
• C. Mass flow rate of the flashing liquid stored at its saturation vapor pressure
• D. Volume flow rate of the liquid

Answer: (C)

In a flashing liquid model, the key idea is that some of the liquid will flash into vapor when pressure drops rapidly, while some remains as liquid. The parameter Qm represents the rate at which mass of the flashing liquid moves through the system, specifically the portion of liquid that is stored at its saturation vapor pressure. This means Qm is the mass flow rate of the liquid that is already at the saturation state and is available to flash to vapor, not the vapor flow itself and not a volume flow. It’s a mass flow rate, measured at the saturation pressure corresponding to the liquid’s temperature.