ReferenceMoistAir

ReferenceMoistAir: Detailed moist air model (143.15 ... 2000 K)

Package Contents

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 humitity per unit mass of moist air at saturation as a function of the thermodynamic state record

xsaturation

Return absolute humitity 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

Package Constants (29)

ThermoStates

Value: Modelica.Media.Interfaces.Choices.IndependentVariables.pTX

Type: IndependentVariables

Description: Enumeration type for independent variables

mediumName

Value: "Moist air"

Type: String

Description: Name of the medium

substanceNames

Value: {"Water", "Air"}

Type: String[:]

Description: Names of the mixture substances. Set substanceNames={mediumName} if only one substance.

extraPropertiesNames

Value: fill("", 0)

Type: String[:]

Description: Names of the additional (extra) transported properties. Set extraPropertiesNames=fill("",0) if unused

singleState

Value: false

Type: Boolean

Description: = true, if u and d are not a function of pressure

reducedX

Value: true

Type: Boolean

Description: = true if medium contains the equation sum(X) = 1.0; set reducedX=true if only one substance (see docu for details)

fixedX

Value: false

Type: Boolean

Description: = true if medium contains the equation X = reference_X

reference_p

Value: 101325

Type: AbsolutePressure (Pa)

Description: Reference pressure of Medium: default 1 atmosphere

reference_T

Value: 298.15

Type: Temperature (K)

Description: Reference temperature of Medium: default 25 deg Celsius

reference_X

Value: {0.01, 0.99}

Type: MassFraction[nX] (kg/kg)

Description: Default mass fractions of medium

p_default

Value: 101325

Type: AbsolutePressure (Pa)

Description: Default value for pressure of medium (for initialization)

T_default

Value: Modelica.SIunits.Conversions.from_degC(20)

Type: Temperature (K)

Description: Default value for temperature of medium (for initialization)

h_default

Value: specificEnthalpy_pTX(p_default, T_default, X_default)

Type: SpecificEnthalpy (J/kg)

Description: Default value for specific enthalpy of medium (for initialization)

X_default

Value: reference_X

Type: MassFraction[nX] (kg/kg)

Description: Default value for mass fractions of medium (for initialization)

C_default

Value: fill(0, nC)

Type: ExtraProperty[nC]

Description: Default value for trace substances of medium (for initialization)

nS

Value: size(substanceNames, 1)

Type: Integer

Description: Number of substances

nX

Value: nS

Type: Integer

Description: Number of mass fractions

nXi

Value: if fixedX then 0 else if reducedX then nS - 1 else nS

Type: Integer

Description: Number of structurally independent mass fractions (see docu for details)

nC

Value: size(extraPropertiesNames, 1)

Type: Integer

Description: Number of extra (outside of standard mass-balance) transported properties

C_nominal

Value: 1.0e-6 * ones(nC)

Type: Real[nC]

Description: Default for the nominal values for the extra properties

fluidConstants

Value: {Utilities.Water95_Utilities.waterConstants, Modelica.Media.Air.ReferenceAir.airConstants}

Type: FluidConstants[nS]

Description: Constant data for the fluid

Water

Value: 1

Type: Integer

Description: Index of water (in substanceNames, massFractions X, etc.)

Air

Value: 2

Type: Integer

Description: Index of air (in substanceNames, massFractions X, etc.)

useEnhancementFactor

Value: false

Type: Boolean

Description: Use the enhancement factor in the calculations

useDissociation

Value: true

Type: Boolean

Description: Take dissociation into account for high temperatures

k_mair

Value: steam.MM / dryair.MM

Type: Real

Description: Ratio of molar weights

dryair

Value: ReferenceAir.Air_Utilities.Basic.Constants

Type: FundamentalConstants

steam

Value: Utilities.Water95_Utilities.Constants

Type: FundamentalConstants

MMX

Value: {steam.MM, dryair.MM}

Type: MolarMass[2] (kg/mol)

Description: Molar masses of components

Information

This information is part of the Modelica Standard Library maintained by the Modelica Association.

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
xw Absolutue humidity in kg(water)/kg(dry air)
xws Absolutue 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

  • Dry air:
    • d,h,u,s,cp from [1]
    • λ, η from [2]
  • Steam:
    • d,h,u,s,cp 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 (xw > xwsw) 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]
  • cp is not defined
  • λ, η of liquid droplets from [5] and [6]

Ice fog (xw > xwsw) 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]
  • cp is not defined
  • λ of ice as constant value
  • η of ice is neglected
Saturation pressure of water in moist air

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

  • f is the enhancement factor from [9] and [3]
  • psat for T ≥ 273.16 K is the saturation pressure from [4]
  • psat 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).

Copyright © 2013-2019, Modelica Association and contributors

Extended by (1)

Medium

Modelica.Media.Examples.ReferenceAir.MoistAir

Medium model