Question Bank • QB_SUB_APE_0005 NAT • 2 Marks

Section 6: Agricultural Process Engineering

Evaporation and Drying

Subtopic: Psychrometry – properties of air-water vapour mixture

Question Statement:

At standard atmospheric pressure ($101.325\text{ kPa}$), moist air has a water vapor partial pressure of $p_v = 2.0\text{ kPa}$. The humidity ratio $W$ (in kg water/kg dry air, rounded to 4 decimal places) is:

Answer Key:

0.0125

Step-by-Step Solution & Explanation

Humidity ratio formula: $W = 0.622 \frac{p_v}{P_{\text{atm}} - p_v} = 0.622 \frac{2.0}{101.325 - 2.0} = 0.622 \frac{2.0}{99.325} = 0.01253\text{ kg/kg dry air}$
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