Buildings.Media.GasesConstantDensity.SimpleAir

Information

This medium model is similar to Modelica.Media.Air.SimpleAir, except that the gas density is constant.

The use of a constant density avoids having pressure as a state variable in mixing volumes. Hence, fast transients introduced by a change in pressure are avoided. The drawback is that the dimensionality of the coupled nonlinear equation system is typically larger for flow networks.

As in Modelica.Media.Air.SimpleAir, the specific enthalpy h and specific internal energy u are only a function of temperature T and all other provided medium quantities are constant.

Package Content

Name	Description
fluidConstants=FluidConstants(iupacName={"simple air"}, casRegistryNumber={"not a real substance"}, chemicalFormula={"N2, O2"}, structureFormula={"N2, O2"}, molarMass=Modelica.Media.IdealGases.Common.SingleGasesData.N2.MM)	constant data for the fluid
pStp=101325	Pressure for which dStp is defined
dStp=1.2	Fluid density at pressure pStp
BaseProperties	Basic medium properties
setState_dTX	Return thermodynamic state from d, T, and X or Xi
density	return density of ideal gas
specificInternalEnergy	Return specific internal energy
specificEntropy	Return specific entropy
enthalpyOfCondensingGas	Enthalpy of steam per unit mass of steam
saturationPressure	Return saturation pressure of condensing fluid
Inherited
cp_const	Constant specific heat capacity at constant pressure
cv_const=cp_const - R_gas	Constant specific heat capacity at constant volume
R_gas	medium specific gas constant
MM_const	Molar mass
eta_const	Constant dynamic viscosity
lambda_const	Constant thermal conductivity
T_min	Minimum temperature valid for medium model
T_max	Maximum temperature valid for medium model
T0=reference_T	Zero enthalpy temperature
ThermodynamicState	Thermodynamic state of ideal gas
FluidConstants	fluid constants
setState_pTX	Return thermodynamic state from p, T, and X or Xi
setState_phX	Return thermodynamic state from p, h, and X or Xi
setState_psX	Return thermodynamic state from p, s, and X or Xi
setSmoothState	Return thermodynamic state so that it smoothly approximates: if x > 0 then state_a else state_b
pressure	Return pressure of ideal gas
temperature	Return temperature of ideal gas
specificEnthalpy	Return specific enthalpy
specificGibbsEnergy	Return specific Gibbs energy
specificHelmholtzEnergy	Return specific Helmholtz energy
dynamicViscosity	Return dynamic viscosity
thermalConductivity	Return thermal conductivity
specificHeatCapacityCp	Return specific heat capacity at constant pressure
specificHeatCapacityCv	Return specific heat capacity at constant volume
isentropicExponent	Return isentropic exponent
velocityOfSound	Return velocity of sound
specificEnthalpy_pTX	Return specific enthalpy from p, T, and X or Xi
temperature_phX	Return temperature from p, h, and X or Xi
density_phX	Return density from p, h, and X or Xi
isentropicEnthalpy	Return isentropic enthalpy
isobaricExpansionCoefficient	Returns overall the isobaric expansion coefficient beta
isothermalCompressibility	Returns overall the isothermal compressibility factor
density_derp_T	Returns the partial derivative of density with respect to pressure at constant temperature
density_derT_p	Returns the partial derivative of density with respect to temperature at constant pressure
density_derX	Returns the partial derivative of density with respect to mass fractions at constant pressure and temperature
molarMass	Returns the molar mass of the medium
setState_pT	Return thermodynamic state from p and T
setState_ph	Return thermodynamic state from p and h
setState_ps	Return thermodynamic state from p and s
setState_dT	Return thermodynamic state from d and T
density_ph	Return density from p and h
temperature_ph	Return temperature from p and h
pressure_dT	Return pressure from d and T
specificEnthalpy_dT	Return specific enthalpy from d and T
specificEnthalpy_ps	Return specific enthalpy from p and s
temperature_ps	Return temperature from p and s
density_ps	Return density from p and s
specificEnthalpy_pT	Return specific enthalpy from p and T
density_pT	Return density from p and T
ThermoStates	Enumeration type for independent variables
mediumName="unusablePartialMedium"	Name of the medium
substanceNames={mediumName}	Names of the mixture substances. Set substanceNames={mediumName} if only one substance.
extraPropertiesNames=fill("", 0)	Names of the additional (extra) transported properties. Set extraPropertiesNames=fill("",0) if unused
singleState	= true, if u and d are not a function of pressure
reducedX=true	= true if medium contains the equation sum(X) = 1.0; set reducedX=true if only one substance (see docu for details)
fixedX=false	= true if medium contains the equation X = reference_X
reference_p=101325	Reference pressure of Medium: default 1 atmosphere
reference_T=298.15	Reference temperature of Medium: default 25 deg Celsius
reference_X=fill(1/nX, nX)	Default mass fractions of medium
p_default=101325	Default value for pressure of medium (for initialization)
T_default=Modelica.SIunits.Conversions.from_degC(20)	Default value for temperature of medium (for initialization)
h_default=specificEnthalpy_pTX(p_default, T_default, X_default)	Default value for specific enthalpy of medium (for initialization)
X_default=reference_X	Default value for mass fractions of medium (for initialization)
nS=size(substanceNames, 1)	Number of substances
nX=nS	Number of mass fractions
nXi=if fixedX then 0 else if reducedX then nS - 1 else nS	Number of structurally independent mass fractions (see docu for details)
nC=size(extraPropertiesNames, 1)	Number of extra (outside of standard mass-balance) transported properties
C_nominal=1.0e-6*ones(nC)	Default for the nominal values for the extra properties
prandtlNumber	Return the Prandtl number
heatCapacity_cp	alias for deprecated name
heatCapacity_cv	alias for deprecated name
beta	alias for isobaricExpansionCoefficient for user convenience
kappa	alias of isothermalCompressibility for user convenience
density_derp_h	Return density derivative w.r.t. pressure at const specific enthalpy
density_derh_p	Return density derivative w.r.t. specific enthalpy at constant pressure
specificEntropy_pTX	Return specific enthalpy from p, T, and X or Xi
density_pTX	Return density from p, T, and X or Xi
temperature_psX	Return temperature from p,s, and X or Xi
density_psX	Return density from p, s, and X or Xi
specificEnthalpy_psX	Return specific enthalpy from p, s, and X or Xi
AbsolutePressure	Type for absolute pressure with medium specific attributes
Density	Type for density with medium specific attributes
DynamicViscosity	Type for dynamic viscosity with medium specific attributes
EnthalpyFlowRate	Type for enthalpy flow rate with medium specific attributes
MassFlowRate	Type for mass flow rate with medium specific attributes
MassFraction	Type for mass fraction with medium specific attributes
MoleFraction	Type for mole fraction with medium specific attributes
MolarMass	Type for molar mass with medium specific attributes
MolarVolume	Type for molar volume with medium specific attributes
IsentropicExponent	Type for isentropic exponent with medium specific attributes
SpecificEnergy	Type for specific energy with medium specific attributes
SpecificInternalEnergy	Type for specific internal energy with medium specific attributes
SpecificEnthalpy	Type for specific enthalpy with medium specific attributes
SpecificEntropy	Type for specific entropy with medium specific attributes
SpecificHeatCapacity	Type for specific heat capacity with medium specific attributes
SurfaceTension	Type for surface tension with medium specific attributes
Temperature	Type for temperature with medium specific attributes
ThermalConductivity	Type for thermal conductivity with medium specific attributes
PrandtlNumber	Type for Prandtl number with medium specific attributes
VelocityOfSound	Type for velocity of sound with medium specific attributes
ExtraProperty	Type for unspecified, mass-specific property transported by flow
CumulativeExtraProperty	Type for conserved integral of unspecified, mass specific property
ExtraPropertyFlowRate	Type for flow rate of unspecified, mass-specific property
IsobaricExpansionCoefficient	Type for isobaric expansion coefficient with medium specific attributes
DipoleMoment	Type for dipole moment with medium specific attributes
DerDensityByPressure	Type for partial derivative of density with resect to pressure with medium specific attributes
DerDensityByEnthalpy	Type for partial derivative of density with resect to enthalpy with medium specific attributes
DerEnthalpyByPressure	Type for partial derivative of enthalpy with resect to pressure with medium specific attributes
DerDensityByTemperature	Type for partial derivative of density with resect to temperature with medium specific attributes
Choices	Types, constants to define menu choices

Types and constants

  constant FluidConstants[nS] fluidConstants=
    FluidConstants(iupacName={"simple air"},
                   casRegistryNumber={"not a real substance"},
                   chemicalFormula={"N2, O2"},
                   structureFormula={"N2, O2"},
                   molarMass=Modelica.Media.IdealGases.Common.SingleGasesData.N2.MM) 
  "constant data for the fluid";

   constant AbsolutePressure pStp = 101325 "Pressure for which dStp is defined";

   constant Density dStp = 1.2 "Fluid density at pressure pStp";

Buildings.Media.GasesConstantDensity.SimpleAir.BaseProperties

Parameters

Type	Name	Default	Description
Advanced
Boolean	preferredMediumStates	false	= true if StateSelect.prefer shall be used for the independent property variables of the medium

Modelica definition

redeclare replaceable model BaseProperties "Basic medium properties"
   // declarations from Modelica.Media.Interfaces.PartialMedium
   InputAbsolutePressure p "Absolute pressure of medium";
   InputMassFraction[nXi] Xi(start=reference_X[1:nXi]) 
    "Structurally independent mass fractions";
   InputSpecificEnthalpy h "Specific enthalpy of medium";
   Density d "Density of medium";
   Temperature T "Temperature of medium";
   MassFraction[nX] X(start=reference_X) 
    "Mass fractions (= (component mass)/total mass  m_i/m)";
   SpecificInternalEnergy u "Specific internal energy of medium";
   SpecificHeatCapacity R "Gas constant (of mixture if applicable)";
   MolarMass MM "Molar mass (of mixture or single fluid)";
   ThermodynamicState state "thermodynamic state record for optional functions";
   parameter Boolean preferredMediumStates=false 
    "= true if StateSelect.prefer shall be used for the independent property variables of the medium";
   final parameter Boolean standardOrderComponents = true 
    "if true, and reducedX = true, the last element of X will be computed from the other ones";
   SI.Conversions.NonSIunits.Temperature_degC T_degC=
       Modelica.SIunits.Conversions.to_degC(T) 
    "Temperature of medium in [degC]";
   SI.Conversions.NonSIunits.Pressure_bar p_bar=
    Modelica.SIunits.Conversions.to_bar(p) 
    "Absolute pressure of medium in [bar]";

   // Local connector definition, used for equation balancing check
   connector InputAbsolutePressure = input SI.AbsolutePressure 
    "Pressure as input signal connector";
   connector InputSpecificEnthalpy = input SI.SpecificEnthalpy 
    "Specific enthalpy as input signal connector";
   connector InputMassFraction = input SI.MassFraction 
    "Mass fraction as input signal connector";

   // own declarations

equation 
   if standardOrderComponents then
     Xi = X[1:nXi];

       if fixedX then
         X = reference_X;
       end if;
       if reducedX and not fixedX then
         X[nX] = 1 - sum(Xi);
       end if;
       for i in 1:nX loop
         assert(X[i] >= -1.e-5 and X[i] <= 1 + 1.e-5, "Mass fraction X[" +
                String(i) + "] = " + String(X[i]) + "of substance "
                + substanceNames[i] + "\nof medium " + mediumName + " is not in the range 0..1");
       end for;

   end if;

   assert(p >= 0.0, "Pressure (= " + String(p) + " Pa) of medium \"" +
     mediumName + "\" is negative\n(Temperature = " + String(T) + " K)");

   // new medium equations
   h = specificEnthalpy_pTX(p,T,X);

   // Equation for ideal gas, from h=u+p*v and R*T=p*v, from which follows that  u = h-R*T.
   // u = h-R*T;

   // However, in this medium, the gas law is d=dStp (=constant), from which follows using h=u+pv that
   // u= h-p*v = h-p/d = h-p/dStp
   u = h-p/dStp;

   R = R_gas;
   //    d = p/(R*T);
   d = dStp;// = p/pStp;

   MM = MM_const;
   state.T = T;
   state.p = p;
end BaseProperties;

Buildings.Media.GasesConstantDensity.SimpleAir.setState_dTX

Information

Inputs

Type	Name	Default	Description
Density	d		density [kg/m3]
Temperature	T		Temperature [K]
MassFraction	X[:]	fill(0, 0)	Mass fractions [kg/kg]

Outputs

Type	Name	Description
ThermodynamicState	state	Thermodynamic state

Modelica definition

redeclare function setState_dTX 
  "Return thermodynamic state from d, T, and X or Xi"
   extends Modelica.Icons.Function;
   input Density d "density";
   input Temperature T "Temperature";
   input MassFraction X[:] = fill(0,0) "Mass fractions";
   output ThermodynamicState state "Thermodynamic state";
algorithm 
  ModelicaError("The function 'setState_dTX' must not be used in GasesConstantDensity as
                in this medium model, the pressure cannot be determined from the density.\n");
   state :=setState_pTX(pStp, T, X);
end setState_dTX;

Buildings.Media.GasesConstantDensity.SimpleAir.density

Information

Inputs

Type	Name	Default	Description
ThermodynamicState	state		thermodynamic state record

Outputs

Type	Name	Description
Density	d	Density [kg/m3]

Modelica definition

redeclare function density "return density of ideal gas"
   extends Modelica.Icons.Function;
   input ThermodynamicState state "thermodynamic state record";
   output Density d "Density";
algorithm 
   d := dStp;
end density;

Buildings.Media.GasesConstantDensity.SimpleAir.specificInternalEnergy

Information

Inputs

Type	Name	Default	Description
ThermodynamicState	state		thermodynamic state record

Outputs

Type	Name	Description
SpecificEnergy	u	Specific internal energy [J/kg]

Modelica definition

redeclare function specificInternalEnergy 
  "Return specific internal energy"
  extends Modelica.Icons.Function;
  input ThermodynamicState state "thermodynamic state record";
  output SpecificEnergy u "Specific internal energy";
algorithm 
  u := specificEnthalpy(state) - state.p/dStp;
end specificInternalEnergy;

Buildings.Media.GasesConstantDensity.SimpleAir.specificEntropy

Information

Inputs

Type	Name	Default	Description
ThermodynamicState	state		thermodynamic state record

Outputs

Type	Name	Description
SpecificEntropy	s	Specific entropy [J/(kg.K)]

Modelica definition

redeclare replaceable function specificEntropy 
  "Return specific entropy"
   extends Modelica.Icons.Function;
   input ThermodynamicState state "thermodynamic state record";
   output SpecificEntropy s "Specific entropy";
algorithm 
   s := cp_const*Modelica.Math.log(state.T/T0);// - R_gas*Modelica.Math.log(state.p/reference_p);
end specificEntropy;

Buildings.Media.GasesConstantDensity.SimpleAir.enthalpyOfCondensingGas

Information

Inputs

Type	Name	Default	Description
Temperature	T		temperature [K]

Outputs

Type	Name	Description
SpecificEnthalpy	h	steam enthalpy [J/kg]

Modelica definition

replaceable function enthalpyOfCondensingGas 
  "Enthalpy of steam per unit mass of steam"
  extends Modelica.Icons.Function;
  input Temperature T "temperature";
  output SpecificEnthalpy h "steam enthalpy";
algorithm 
  h := 0;
end enthalpyOfCondensingGas;

Buildings.Media.GasesConstantDensity.SimpleAir.saturationPressure

Information

Inputs

Type	Name	Default	Description
Temperature	Tsat		saturation temperature [K]

Outputs

Type	Name	Description
AbsolutePressure	psat	saturation pressure [Pa]

Modelica definition

replaceable function saturationPressure 
  "Return saturation pressure of condensing fluid"
  extends Modelica.Icons.Function;
  input Temperature Tsat "saturation temperature";
  output AbsolutePressure psat "saturation pressure";
algorithm 
  psat := 0;
end saturationPressure;

Buildings.Media.GasesConstantDensity.SimpleAir.BaseProperties.InputAbsolutePressure

Modelica definition

connector InputAbsolutePressure = input SI.AbsolutePressure 
  "Pressure as input signal connector";

Buildings.Media.GasesConstantDensity.SimpleAir.BaseProperties.InputMassFraction

Modelica definition

connector InputMassFraction = input SI.MassFraction 
  "Mass fraction as input signal connector";

Buildings.Media.GasesConstantDensity.SimpleAir.BaseProperties.InputSpecificEnthalpy

Modelica definition

connector InputSpecificEnthalpy = input SI.SpecificEnthalpy 
  "Specific enthalpy as input signal connector";