Question Bank • QB_APE_010 NAT • 2 Marks

Section 6: Agricultural Process Engineering

Evaporation and Drying

Subtopic: Psychrometry – properties of air-water vapour mixture

Question Statement:

The specific enthalpy ($h$) of moist air at dry-bulb temperature $T = 30^\circ\text{C}$ and humidity ratio $W = 0.015\text{ kg water/kg dry air}$ calculated using the standard psychrometric equation $h = 1.006 T + W (2501 + 1.86 T)$ in $\text{kJ/kg dry air}$ is ________ (round off to 1 decimal place).

Answer Key:

68.5

Step-by-Step Solution & Explanation

Standard enthalpy equation for moist air: $h = 1.006 T + W (2501 + 1.86 T)$ Substitute $T = 30^\circ\text{C}$ and $W = 0.015$: $1.006 \times 30 = 30.18$ $2501 + 1.86(30) = 2501 + 55.8 = 2556.8$ $W \times 2556.8 = 0.015 \times 2556.8 = 38.352$ $h = 30.18 + 38.352 = 68.532\text{ kJ/kg dry air} \approx 68.5\text{ kJ/kg dry air}$
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