ABSTRACT
Moist air is a two-phase mixture of dry air and water vapor that needs to be treated separately from dry air since its physical properties are different. The homogeneous mixture of dry air and water vapor that do not react with each other and do not change in chemical composition is considered a pure substance. Since in commercial wood dryers the working pressures of the moist air are low, both the dry air and the water vapor can be assumed to behave like ideal gases, and the moist air as an ideal gas mixture. The amount of water vapor varies from zero (dry air) to a maximum, depending on the mixture's temperature and pressure. Relative humidity (RH) is the ratio of the mole fraction of water vapor in a given moist air sample to the mole fraction in a saturated air sample at the same temperature and total pressure.
