Theory
Both inputs end in the same quantity, the mole fraction of water vapour, which fixes the mixture of dry air and water vapour (ISO 9613-1, 1993). The relative humidity is converted with the saturation pressure at the gas temperature and the absolute static pressure; it therefore changes with both. The mole fraction is used as entered, whatever the temperature and pressure.
Default and rule
- Default
- Relative humidity
- Rule
Relative humidity.
- Source
ISO 9613-1 (1993), Annex B, for the conversion.
Valid range Relative humidity | Mole fraction
When to use the mole fraction
For gas above 200 °C, or when the water content comes from a combustion or humidifier balance as a molar quantity.