Question

A 6 x 6 x 4 m room contains air at ${25}^{0}C$ and 100 kPa at a relative humidity of 75 %. What is the enthalpy per unit mass of the dry air?

• A. 42.16 kJ/kg of d.A.
• B. 63.68 kJ/kg of d.A.
• C. 54.18 kJ/kg of d.A.
• D. 36.28 kJ/kg of d.A.

Answer 1

The correct option is B 63.68 kJ/kg of d.A.

$\omega =\frac{0.622P_v}{P-P_v}and\frac{P_v}{P_s}=\varphi P_v=\varphi P_s=0.75\times 3.1698P_v=2.377kPa\omega =\frac{6.22\times 2.377}{(100-2.377)}$
= 0.01514 kJ of water vapour/kg of dry air

h = 1.005 T + $\omega$(2500 + 1.88 T)
= 1.005 x 25 + 0.01514 x (2500 + 1.88 x 25)

h = 63.68 kJ/kg of dry air