Question

If h_a is enthalpy of dry air, h_v is enthalpy of water vapour and w is specific humidity, the enthalpy of moist air will be
1. h_a + h_v
2. h_a + wh_v
3. h_v + wh_a
4. h_v + h_a/w 

Answer 1

Correct Answer - Option 2 : h_a + wh_v

Explanation:

Enthalpy of moist air 

Enthalpy of moist air = Enthalpy of dry air + Enthalpy of water vapour associated

⇒ h = hair + ωhvapour

⇒ h = Cpatdb + ω(hg + Cpstdb)

We have Cpa = 1.005 kJ/kg K, Cps = 1.88 kJ/kg K

⇒ h = 1.005 tdb + ω (2500 + 1.88tdb)