ESS55
Prof. Jin-Yi Yu
Virtual Temperature
qMoist air has a lower
apparent molecular weight that dry air.
čThe gas constant for 1
kg of moist air is larger than that for 1 kg of dry air.
č But the exact value of the gas constant of
moist air would depend on the amount of water
vapor contained in the air.
čIt is inconvenient to
calculate the gas constant for moist air.
qIt is more convenient
to retain the gas constant of dry air and use a fictitious temperature in the ideal gas equation.
čThis fictitious
temperature is called “virtual temperature”.
čThis is the temperature
that dry air must have in order to has the same density as the moist air at the same pressure.
čSince moist air is less
dense that dry air, the virtual temperature is always greater than the actual temperature.