.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.

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
xw Absolute humidity in kg(water)/kg(dry air)
xws 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 ≤ xw ≤ xws)

Ideal mixture of dry air and steam

Supersaturated humid air (liquid fog and ice fog)

Liquid fog (xw > xwsw) and T ≥ 273.16 K

Ideal mixture of saturated humid air and water

Ice fog (xw > xwsw) and T < 273.16 K

Ideal mixture of saturated humid air and ice

Saturation pressure of water in moist air

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

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).

Copyright © 2013-2020, Modelica Association and contributors

Contents

NameDescription
ThermodynamicStateThermodynamicState record for moist air
BasePropertiesMoist air base properties record
setState_pTXReturn thermodynamic state as function of pressure p, temperature T and composition X
setState_phXReturn thermodynamic state as function of pressure p, specific enthalpy h and composition X
setState_psXReturn thermodynamic state as function of pressure p, specific enthalpy h and composition X
setState_dTXReturn thermodynamic state as function of density d, temperature T and composition X
setSmoothStateReturn thermodynamic state so that it smoothly approximates: if x > 0 then state_a else state_b
XsaturationReturn absolute humidity per unit mass of moist air at saturation as a function of the thermodynamic state record
xsaturationReturn absolute humidity per unit mass of dry air at saturation as a function of the thermodynamic state record
massFraction_pTphiReturn mass fractions as a function of pressure, temperature and relative humidity
massFractionWaterVaporReturn mass fraction of water vapor
massFractionWaterNonVaporReturn mass fraction of liquid and solid water
massFractionSaturationReturn saturation mass fractions
massFractionSaturation_ppsatReturn mass fvraction at saturation boundary given pressure and saturation pressure
massFraction_waterContentReturn mass fractions as a function of pressure, temperature and absolute humidity in kg(water)/kg(dry air)
waterContent_XReturn water content in kg(water)/kg(dry air) given mass fractions
relativeHumidityReturn relative humidity
gasConstantReturn ideal gas constant as a function from thermodynamic state, only valid for phi<1
saturationPressureLiquidReturn saturation pressure of water as a function of temperature T
sublimationPressureIceReturn sublimation pressure of water as a function of temperature T between 223.16 and 273.16 K
saturationPressureReturn saturation pressure of condensing fluid
saturationTemperatureReturn saturation temperature of condensing fluid
enthalpyOfVaporizationReturn enthalpy of vaporization of water
enthalpyOfLiquidReturn enthalpy of liquid water
enthalpyOfGasReturn specific enthalpy of gas (air and steam)
enthalpyOfCondensingGasReturn specific enthalpy of steam
enthalpyOfNonCondensingGasReturn specific enthalpy of dry air
enthalpyOfDryAirReturn specific enthalpy of dry air
enthalpyOfWaterReturn specific enthalpy of water (solid + liquid + steam)
enthalpyOfWaterVaporReturn specific enthalpy of steam
enthalpyOfWaterNonVaporReturn enthalpy of liquid and solid water
pressureReturns pressure of ideal gas as a function of the thermodynamic state record
temperatureReturn temperature of ideal gas as a function of the thermodynamic state record
densityReturns density as a function of the thermodynamic state record
specificEnthalpyReturn specific enthalpy of moist air as a function of the thermodynamic state record
specificInternalEnergyReturn specific internal energy of moist air as a function of the thermodynamic state record
specificEntropyReturn specific entropy from thermodynamic state record, only valid for phi<1
specificGibbsEnergyReturn specific Gibbs energy as a function of the thermodynamic state record, only valid for phi<1
specificHelmholtzEnergyReturn specific Helmholtz energy as a function of the thermodynamic state record, only valid for phi<1
specificHeatCapacityCpReturn specific heat capacity at constant pressure as a function of the thermodynamic state record
specificHeatCapacityCvReturn specific heat capacity at constant volume as a function of the thermodynamic state record
isentropicExponentReturn isentropic exponent
isentropicEnthalpyReturn isentropic enthalpy
velocityOfSoundReturn velocity of sound
molarMassReturn the molar mass of the medium
dynamicViscosityReturn dynamic viscosity as a function of the thermodynamic state record, valid from 73.15 K to 373.15 K
thermalConductivityReturn thermal conductivity as a function of the thermodynamic state record, valid from 73.15 K to 373.15 K
UtilitiesUtility package for moist air

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