.Modelica.Media.Air.ReferenceMoistAir

Information

Calculation of fluid properties for moist air in the region from 143.15 Kelvin to 2000 Kelvin at pressures up to 10 MPa. This model of moist air is based on the diploma thesis of Hellriegel [10] with small modifications. Moist air is treated as an ideal mixture of the real fluids air and water.

Restriction

The functions provided by this package shall be used inside of the restricted limits according to the referenced literature.

611.2 Pa ≤ p ≤ 10 MPa
143.15 K ≤ T ≤ 2000 K

Usage

The package MoistAir can be used as any other medium model (see User's Guide of Media Library for further information). The package defines two boolean constants useEnhancementFactor and useDissociation, which give the user fine grained control of the calculations.

Constant	Default Value	Meaning
useEnhancementFactor	false	The enhancement factor is used in the calculation of the saturation partial pressure of water in moist air. It is always very close to 1 except for high pressures (>2 MPa) and low temperatures (<233.15 K). For pressures less than 1 MPa this factor can be safely set to 1. Its calculation is very expensive, since it can only be calculated by an iterative method.
useDissociation	true	The effect of dissociation is taken into account for temperatures greater than 773.15 K.

Calculation algorithms

Nomenclature

p	Mixture pressure in Pa
T	Temperature in K
x_w	Absolute humidity in kg(water)/kg(dry air)
x_ws	Absolute humidity on saturation boundary in kg(water)/kg(dry air)
φ	Relative humidity (only defined for unsaturated humid air)

Unsaturated and saturated humid air (0 ≤ x_w ≤ x_ws)

Ideal mixture of dry air and steam

Dry air:
- d,h,u,s,c_p from [1]
- λ, η from [2]
Steam:
- d,h,u,s,c_p from [4]
- λ, η for 273.15 K ≤ T ≤ 1073.15 K from [5] and [6]
- λ, η for T < 273.15 K or T > 1073.15 K from [12]

Supersaturated humid air (liquid fog and ice fog)

Liquid fog (x_w > x_wsw) and T ≥ 273.16 K

Ideal mixture of saturated humid air and water

Saturated humid air (see above)
d,h,u,s of liquid droplets from [4]
c_p is not defined
λ, η of liquid droplets from [5] and [6]

Ice fog (x_w > x_wsw) and T < 273.16 K

Ideal mixture of saturated humid air and ice

Saturated humid air (see above)
d,h,u,s of ice crystals from [7]
c_p is not defined
λ of ice as constant value
η of ice is neglected

Saturation pressure of water in moist air

The saturation pressure p_ds of water in moist air is calculated by p_ds = f*p_sat, where

f is the enhancement factor from [9] and [3]
p_sat for T ≥ 273.16 K is the saturation pressure from [4]
p_sat for T < 273.16 K is the saturation pressure from [8]

Dissociation

For temperatures above 773.15 K effects of dissociation are taken into account. Dissociation is modeled according to [11]. For high temperatures the calculated values for moist air with 0 kg(water)/kg(dry air) (i.e. dry air) may differ from those calculated by the package Modelica.Media.Air.ReferenceAir, because there no dissociation is considered.

References

[1] Thermodynamic Properties of Air and Mixtures of Nitrogen, Argon, and Oxygen From 60 to 2000 K at Pressures to 2000 MPa. J. Phys. Chem. Ref. Data, Vol. 29, No. 3, 2000.

[2] Viscosity and Thermal Conductivity Equations for Nitrogen, Oxygen, Argon, and Air. International Journal of Thermophysics, Vol. 25, No. 1, January 2004

[3] Revised Release on the IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use. 2009 International Association for the Properties of Water and Steam.

[4] Revised Release on the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam. 2007 International Association for the Properties of Water and Steam.

[5] Release on the IAPWS Formulation 2008 for the Viscosity of Ordinary Water Substance. 2008 International Association for the Properties of Water and Steam

[6] Release on the IAPWS Formulation 2011 for the Thermal Conductivity of Ordinary Water Substance. 2011 International Association for the Properties of Water and Steam.

[7] Revised Release on the Equation of State 2006 for H2O Ice Ih. 2009 International Association for the Properties of Water and Steam.

[8] Revised Release on the Pressure along the Melting and Sublimation Curves of Ordinary Water Substance. 2011 International Association for the Properties of Water and Steam.

[9] Determination of Thermodynamic and Transport Properties of Humid Air for Power-Cycle Calculations. 2009 PTB, Braunschweig, Germany.

[10] Berechnung der thermodynamischen Zustandsfunktionen von feuchter Luft in energietechnischen Prozessmodellierungen. 2001 Diplomarbeit, Zittau.

[11] Thermodynamische Stoffwerte von feuchter Luft und Verbrennungsgasen. 2003 VDI-Richtlinie 4670.

[12] Wärmeübertragung in Dampferzeugern und Wärmetauschern. 1985 FDBR-Fachbuchreihe, Bd. 2, Vulkan Verlag Essen.

References

Lemmon, E. W., Jacobsen, R. T., Penoncello, S. G., Friend, D. G.:: Thermodynamic Properties of Air and Mixtures of Nitrogen, Argon, and Oxygen From 60 to 2000 K at Pressures to 2000 MPa. J. Phys. Chem. Ref. Data, Vol. 29, No. 3, 2000.
Lemmon, E. W., Jacobsen, R. T.:: Viscosity and Thermal Conductivity Equations for Nitrogen, Oxygen, Argon, and Air. International Journal of Thermophysics, Vol. 25, No. 1, January 2004

Verification

The verification report for the development of this library is provided here.

Acknowledgment

This library was developed by XRG Simulation GmbH as part of the Clean Sky JTI project (Project title: MoMoLib-Modelica Model Library Development for Media, Magnetic Systems and Wavelets; Project number: 296369; Theme: JTI-CS-2011-1-SGO-02-026: Modelica Model Library Development Part I). The partial financial support for the development of this library by the European Union is highly appreciated.

Some parts of this library refer to the ThermoFluid library developed at Lund University (http://thermofluid.sourceforge.net).

Name	Description
ThermodynamicState	ThermodynamicState record for moist air
BaseProperties	Moist air base properties record
setState_pTX	Return thermodynamic state as function of pressure p, temperature T and composition X
setState_phX	Return thermodynamic state as function of pressure p, specific enthalpy h and composition X
setState_psX	Return thermodynamic state as function of pressure p, specific enthalpy h and composition X
setState_dTX	Return thermodynamic state as function of density d, temperature T and composition X
setSmoothState	Return thermodynamic state so that it smoothly approximates: if x > 0 then state_a else state_b
Xsaturation	Return absolute humidity per unit mass of moist air at saturation as a function of the thermodynamic state record
xsaturation	Return absolute humidity per unit mass of dry air at saturation as a function of the thermodynamic state record
massFraction_pTphi	Return mass fractions as a function of pressure, temperature and relative humidity
massFractionWaterVapor	Return mass fraction of water vapor
massFractionWaterNonVapor	Return mass fraction of liquid and solid water
massFractionSaturation	Return saturation mass fractions
massFractionSaturation_ppsat	Return mass fvraction at saturation boundary given pressure and saturation pressure
massFraction_waterContent	Return mass fractions as a function of pressure, temperature and absolute humidity in kg(water)/kg(dry air)
waterContent_X	Return water content in kg(water)/kg(dry air) given mass fractions
relativeHumidity	Return relative humidity
gasConstant	Return ideal gas constant as a function from thermodynamic state, only valid for phi<1
saturationPressureLiquid	Return saturation pressure of water as a function of temperature T
sublimationPressureIce	Return sublimation pressure of water as a function of temperature T between 223.16 and 273.16 K
saturationPressure	Return saturation pressure of condensing fluid
saturationTemperature	Return saturation temperature of condensing fluid
enthalpyOfVaporization	Return enthalpy of vaporization of water
enthalpyOfLiquid	Return enthalpy of liquid water
enthalpyOfGas	Return specific enthalpy of gas (air and steam)
enthalpyOfCondensingGas	Return specific enthalpy of steam
enthalpyOfNonCondensingGas	Return specific enthalpy of dry air
enthalpyOfDryAir	Return specific enthalpy of dry air
enthalpyOfWater	Return specific enthalpy of water (solid + liquid + steam)
enthalpyOfWaterVapor	Return specific enthalpy of steam
enthalpyOfWaterNonVapor	Return enthalpy of liquid and solid water
pressure	Returns pressure of ideal gas as a function of the thermodynamic state record
temperature	Return temperature of ideal gas as a function of the thermodynamic state record
density	Returns density as a function of the thermodynamic state record
specificEnthalpy	Return specific enthalpy of moist air as a function of the thermodynamic state record
specificInternalEnergy	Return specific internal energy of moist air as a function of the thermodynamic state record
specificEntropy	Return specific entropy from thermodynamic state record, only valid for phi<1
specificGibbsEnergy	Return specific Gibbs energy as a function of the thermodynamic state record, only valid for phi<1
specificHelmholtzEnergy	Return specific Helmholtz energy as a function of the thermodynamic state record, only valid for phi<1
specificHeatCapacityCp	Return specific heat capacity at constant pressure as a function of the thermodynamic state record
specificHeatCapacityCv	Return specific heat capacity at constant volume as a function of the thermodynamic state record
isentropicExponent	Return isentropic exponent
isentropicEnthalpy	Return isentropic enthalpy
velocityOfSound	Return velocity of sound
molarMass	Return the molar mass of the medium
dynamicViscosity	Return dynamic viscosity as a function of the thermodynamic state record, valid from 73.15 K to 373.15 K
thermalConductivity	Return thermal conductivity as a function of the thermodynamic state record, valid from 73.15 K to 373.15 K
Utilities	Utility package for moist air