Which quantity represents the fraction of the total mass that is in vapor form in a liquid–vapor mixture?

Which quantity represents the fraction of the total mass that is in vapor form in a liquid–vapor mixture?

• A. Vapor Quality
• B. Moisture Content of Vapor
• C. Saturation Temperature
• D. Specific Humidity

Answer: (A)

In a saturated liquid–vapor mixture, the quantity that represents how much of the total mass is in the vapor phase is called the vapor quality. It is defined as x = m_v / (m_l + m_v), the mass of vapor divided by the total mass. This is exactly the fraction of the total mass that is in vapor form, and it ranges from 0 (all liquid) to 1 (all vapor). Vapor quality is also how we relate mixture properties to the pure-phase properties, for example v = (1 − x) v_f + x v_g and h = h_f + x h_fg, where v_f and v_g are the saturated liquid and vapor specific volumes, and h_f and h_fg are associated enthalpies. Saturation temperature is simply the temperature at which the liquid and vapor are in equilibrium at a given pressure, not a mass fraction. Specific humidity describes moisture content in air, not the fraction of mass in a liquid–vapor mixture. Moisture content of vapor is not the standard term used for this fraction in steam calculations.

In a saturated liquid–vapor mixture, the quantity that represents how much of the total mass is in the vapor phase is called the vapor quality. It is defined as x = m_v / (m_l + m_v), the mass of vapor divided by the total mass. This is exactly the fraction of the total mass that is in vapor form, and it ranges from 0 (all liquid) to 1 (all vapor). Vapor quality is also how we relate mixture properties to the pure-phase properties, for example v = (1 − x) v_f + x v_g and h = h_f + x h_fg, where v_f and v_g are the saturated liquid and vapor specific volumes, and h_f and h_fg are associated enthalpies.

Saturation temperature is simply the temperature at which the liquid and vapor are in equilibrium at a given pressure, not a mass fraction. Specific humidity describes moisture content in air, not the fraction of mass in a liquid–vapor mixture. Moisture content of vapor is not the standard term used for this fraction in steam calculations.