Humid Air : Enthalpy

Air psychrometrics

1. Introduction

The enthalpy of the humid air is, at a given pressure, the energy necessary to heat 1 kg of dry air from the reference temperature T0 to the temperature T, to vaporize at T0 the quantity of water in the humid air having an absolute humidity of ω, and to heat up the water vapor from T0 to T.

2. Calculation

General form

H' = Cp'.(T-T0) + ω.Λ0

With :

H' = enthalpy of humid air (J/kg_dry_air)
Cp' = specific heat of humid air (J/K/kg_dry_air)
T = temperature of calculation (K)
T0 = temperature of reference (K)
ω = Absolute humidity of air (-)
Λ0 = vaporization enthalpy at T0 (J/kg)

In practice, at 273 K

H' = (1005 + 1884*ω).(T-273) + 2.5023.106