Step 1: Understanding the Concept:
In drying operations, several humidity parameters describe the state of moist air, but only one of them coincides numerically with the adiabatic saturation temperature for an air-water system.
Step 2: Key Concept or Approach:
Recall the Lewis relation, which applies specifically to air-water mixtures and links the wet bulb temperature to the adiabatic saturation temperature.
Step 3: Detailed Explanation:
Absolute humidity is a mass ratio of water vapor to dry air, not a temperature, so it cannot equal another temperature term.
Relative humidity is a percentage comparing actual and saturation vapor pressures, again not a temperature.
Dew point is the temperature at which air becomes saturated on cooling alone, without evaporation into the air stream, so it stays a separate quantity from adiabatic saturation temperature.
Wet bulb temperature is measured by evaporative cooling of a wetted wick in a moving air stream, and for the special case of air and water vapor, the ratio of heat to mass transfer coefficients works out so that wet bulb temperature equals the adiabatic saturation temperature.
Step 4: Final Answer:
The parameter equal to the adiabatic saturation temperature during drying is the wet bulb temperature.