Subtopic: Psychrometry – properties of air-water vapour mixture
Question Statement:
Which of the following statements regarding psychrometric processes in agricultural crop drying is/are CORRECT?
Options:
(A) Sensible heating of ambient air increases both its dry-bulb temperature and enthalpy while keeping humidity ratio constant
(B) In an adiabatic drying process, the wet-bulb temperature of the drying air remains essentially constant
(C) Relative humidity increases when moist air is sensibly heated
(D) The dew point temperature is determined solely by the partial pressure of water vapor in the moist air
Answer Key:
A, B, D
Step-by-Step Solution & Explanation
- Statement A is correct: Sensible heating adds thermal energy without adding moisture, so dry-bulb temperature and enthalpy increase while humidity ratio $W$ remains constant.
- Statement B is correct: Adiabatic evaporative cooling during drying converts sensible heat into latent heat along a constant wet-bulb / enthalpy line ($T_{wb} \approx \text{constant}$).
- Statement C is incorrect: Sensible heating increases saturation vapor pressure $P_{vs}$, causing relative humidity $RH = P_v / P_{vs}$ to decrease.
- Statement D is correct: Dew point temperature is the saturation temperature corresponding to the partial pressure of water vapor $P_v$, invariant to sensible temperature changes.