MoistAir isentropicExponent() and specificEntropy()

[RaphaelGebhart]

Closes #4728 (Runtime warning).

Test model:

package MoistAirTests "Tests MoistAir isentropicExponent() and specificEntropy()"
  extends Modelica.Icons.Package;

  model IsentropicExponent
    extends Modelica.Icons.Example;
    package Medium = Modelica.Media.Air.MoistAir;

    Medium.AbsolutePressure p = Medium.p_default;
    Medium.Temperature T = Medium.T_default;
    Real x_sat = Medium.xsaturation_pT(p,T) "[kg_H2O/kg_dryAir] at saturation";
    Medium.MassFraction X_sat = x_sat/(1+x_sat) "[kg_H2O/kg_tot] at saturation";
    Medium.MassFraction X = (0.99 + 0.02*time)*X_sat "[kg_H2O/kg_tot]";
    Real x = X/(1-X) "[kg_H2O/kg_dryAir]";

    Medium.ThermodynamicState state = Medium.setState_pTX(p,T,{X});

    Real phi = Medium.relativeHumidity(state) "p_H2O/p_H2O,sat";
    Real psi = x/x_sat;

    Medium.IsentropicExponent kappa = Medium.isentropicExponent(state); // Isentropic exponent is heavily discontinuous at phi = psi = 1, phi < 0.998 is on the safe side, phi < 0.999 is also fine IMO
    Medium.IsentropicExponent  kappa_ref = 1.39811 "Reference isentropic exponent";
    Real eps_rel_kappa = abs(kappa-kappa_ref)/kappa_ref;

  end IsentropicExponent;

  model IsentropicExponentAndSpecificEntropy
    extends Modelica.Icons.Example;
    package Medium = Modelica.Media.Air.MoistAir;

    Medium.AbsolutePressure p = 1e5;
    Medium.Temperature T = 293.15 + 20*cos(10*time);
    Medium.MassFraction X = 1e-2;
    Medium.ThermodynamicState state = Medium.setState_pTX(p,T,{X});

    Medium.MassFraction X_sat =  Medium.Xsaturation(state);
    Real x_sat = Medium.xsaturation_pT(p,T) "[kg_H2O/kg_dryAir] at saturation";
    Real x = X/(1-X) "[kg_H2O/kg_dryAir]";

    Real phi = Medium.relativeHumidity(state) "p_H2O/p_H2O,sat";
    Real psi = x/x_sat;

    Medium.SpecificEntropy s = Medium.specificEntropy(state); // Specific entropy is continuous at phi = psi = 1
    Medium.IsentropicExponent kappa = Medium.isentropicExponent(state); // Isentropic exponent is heavily discontinuous at phi = psi = 1, phi < 0.998 is on the safe side, phi < 0.999 is also fine IMO

  end IsentropicExponentAndSpecificEntropy;

  model SpecificEntropy "Checks MoistAir.specificEntropy()"
    extends Modelica.Icons.Example;
    package Medium = Modelica.Media.Air.MoistAir;

    Medium.AbsolutePressure p = Medium.p_default;
    Medium.Temperature T = Medium.T_default;
    Real x_sat = Medium.xsaturation_pT(p,T) "[kg_H2O/kg_dryAir] at saturation";
    Medium.MassFraction X_sat = x_sat/(1+x_sat) "[kg_H2O/kg_tot] at saturation";
    Medium.MassFraction X = (0 + 2*time)*X_sat "[kg_H2O/kg_tot]";
    Real x = X/(1-X) "[kg_H2O/kg_dryAir]";

    Medium.ThermodynamicState state = Medium.setState_pTX(p,T,{X});

    Medium.SpecificEntropy s = Medium.specificEntropy(state); // Specific entropy is continuous at phi = psi = 1
    Real phi = Medium.relativeHumidity(state) "p_H2O/p_H2O,sat";
    Real psi = x/x_sat;

  end SpecificEntropy;

end MoistAirTests;