modelMoistAir

Moist air

Extends from Modelica.Icons.MaterialProperty (Icon for property classes).

Information

This is the moist air model that is based on Mollier Diagram.

In the HVAC systems, the air is generally considered as a binary mixture of dry air and water vapor, i.e. moist air. State properties of moist air are calculated by using the Dalton’s law on perfect gas mixtures.

In order to find out the thermodynamic state of the moist air, we use the Gibbs’ phase rule

F = C − P + 2

where C is the number of components (in this case, vapor and dry air), P the number of phases in thermodynamic equilibrium (in this case the only phase is the gas one), and F the number of degrees of freedom.

Thus, dealing with moist air, C is two (vapor and dry air), P is one (gas phase only) and therefore F is equal to three. So we need to know the total pressure, the specific enthalpy h (using convetion that h=0 if T=0°C and no water vapour is present), and the mass fraction X, which is the vapor and dry air mass ratio.

Components

TypeNameDefaultDescription
SI.Pressureppressure
SI.TemperatureTtemperature
SI.MassFractionXabsolute humidity [kg vap/kg da]
SI.MassFractionxvapour mass fraction [kg vap/kg tot]
SI.Pressurepvvapour partial pressure
SI.Pressurepvsvapour saturation pressure
Realphirelative humidity
SI.TemperatureTwbwet bulb temperature
SI.MassFractionXsabsolute humidity [kg vap/kg da] at saturation (phi=1)
SI.MassFractionxsvapour fraction [kg vap/kg tot] at saturation (phi=1)
SI.SpecificEnthalpyhaspecific enthalpy of dry air [J/kg da]
SI.SpecificEnthalpyhvspecific enthalpy of vapour [J/kg vap]
SI.SpecificEnthalpyhspecific enthalpy of moist air [J/kg da]
SI.SpecificEnthalpyhlspecific enthalpy of liquid water at T [J/kg liq]
SI.Densityddensity of moist air
SI.SpecificHeatCapacitycpmoist air specific heat capacity [J/kg da K]
SI.SpecificHeatCapacityRequivalent gas constant of moist air