Computes the saturation pressure, vapor pressure, humidity ratio and vapor mass fraction from dry-bulb temperature and relative humidity.
Inputs
Moist-air state. Defaults are a comfortable room condition at standard atmospheric pressure.
Dry-bulb temperature in degrees Celsius.
0 to 100 percent.
Standard atmosphere is 101.325 kPa.
Results
Humidity ratio ω
-
Grams of vapor per kg of dry air.
Saturation pressure Pg
-
Vapor partial pressure Pv
-
Vapor mass fraction Y
-
Use as the species mass fraction at CFD inlets.
How it works
Relative humidity is defined against the saturation pressure at the dry-bulb temperature. The calculator evaluates that saturation pressure with the Arden Buck equation, converts it to a vapor partial pressure, then uses the ideal-gas relation between the two components to get the humidity ratio and the vapor mass fraction.
Compute the saturation pressure Pg with the Arden Buck equation (one form above 0 C, one below), in kPa.
Get the vapor partial pressure from the relative humidity: Pv = φ Pg.
Compute the humidity ratio ω = 0.622 Pv / (P - Pv), where 0.622 is the ratio of molar masses of water and dry air.
Convert to the vapor mass fraction Y = ω / (1 + ω).
