Buildings.Media.SimpleAirPTDecoupled

Information

This medium model is identical to Modelica.Media.Air.SimpleAir, except the equation d = p/(R*T) has been replaced with d/dStp = p/pStp where pStd and dStp are constants for a reference temperature and density.

This new formulation often leads to smaller systems of nonlinear equations because pressure and temperature are decoupled, at the expense of accuracy.

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
BaseProperties	Basic medium properties
setState_dTX	Return thermodynamic state from d, T, and X or Xi
density	return density of ideal gas
specificEntropy	Return specific entropy

Buildings.Media.SimpleAirPTDecoupled.BaseProperties

Parameters

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

Modelica definition

redeclare model BaseProperties "Basic medium properties" 
   extends BasePropertiesRecord;
  
   ThermodynamicState state 
    "thermodynamic state variables for optional functions";
   parameter Boolean preferredMediumStates=false 
    "= true if StateSelect.prefer shall be used for the independent property variables of the medium";
   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]";
  constant AbsolutePressure pStp = 101325 "Pressure for which dStp is defined";
  constant Density dStp = 1.2 "Fluid density at pressure pStp";
  
equation 
   h = specificEnthalpy_pTX(p,T,X);
   u = h-R*T;
   R = R_gas;
   //    d = p/(R*T);
   d*pStp = p*dStp;
   MM = MM_const;
   state.T = T;
   state.p = p;
end BaseProperties;

Buildings.Media.SimpleAirPTDecoupled.setState_dTX

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

Modelica definition

redeclare replaceable 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;
algorithm 
   state := ThermodynamicState(p=d/dStp*pStd,T=T);
end setState_dTX;

Buildings.Media.SimpleAirPTDecoupled.density

Inputs

Type	Name	Default	Description
ThermodynamicState	state

Outputs

Type	Name	Description
Density	d	Density [kg/m3]

Modelica definition

redeclare replaceable function extends density 
  "return density of ideal gas" 
algorithm 
   d := dStp*state.p/pStp;
end density;

Buildings.Media.SimpleAirPTDecoupled.specificEntropy

Inputs

Type	Name	Default	Description
ThermodynamicState	state

Outputs

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

Modelica definition

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