Subtopic: Sensible heating process on psychrometric chart
Question Statement:
At State A, the dry-bulb temperature is $20^\circ\text{C}$ and relative humidity is $80\%$. The saturation vapor pressure is $2.34\text{ kPa}$ at $20^\circ\text{C}$ and $7.38\text{ kPa}$ at $40^\circ\text{C}$ (State B). Calculate the relative humidity at State B in percentage ($\%$) after sensible heating (round off to one decimal place).
Answer Key:
25.4
Step-by-Step Solution & Explanation
Actual vapor pressure $p_v = 0.80 \times 2.34 = 1.872\text{ kPa}$. During sensible heating, $p_v$ is constant.
At State B ($40^\circ\text{C}$), $RH_B = \frac{p_v}{p_{vs}(40)} = \frac{1.872}{7.38} = 0.2536 \to 25.4\%$.