Changeset 712

Timestamp:

10/16/2007 05:21:34 PM (15 months ago)

Author:

kproelss

Message:

fixed small bugs in entropy functions for ideal gas mixtures

Location:

Modelica/trunk/Modelica/Media

Files:

• Air.mo (modified) (4 diffs)
• IdealGases/Common/package.mo (modified) (1 diff)

Modelica/trunk/Modelica/Media/Air.mo

@@ -93 +93 @@
     constant IdealGases.Common.DataRecord dryair = IdealGases.Common.SingleGasesData.Air;
     constant IdealGases.Common.DataRecord steam = IdealGases.Common.SingleGasesData.H2O;
+    constant SI.MolarMass[2] MMX = {steam.MM,dryair.MM} 
+      "Molar masses of components";
     
     import Modelica.Media.Interfaces;
@@ -124 +126 @@
       
     protected 
-      constant SI.MolarMass[2] MMX = {steam.MM,dryair.MM} 
-        "Molar masses of components";
-      
       MassFraction X_liquid "Mass fraction of liquid or solid water";
       MassFraction X_steam "Mass fraction of steam water";
@@ -816 +815 @@
 Specific entropy is calculated from the thermodynamic state record, assuming ideal gas behavior and including entropy of mixing. Liquid or solid water is not taken into account, the entire water content X[1] is assumed to be in the vapor state (relative humidity below 1.0).
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+      
     protected 
-     MoleFraction[2] Y = massToMoleFractions(state.X,{steam.MM,dryair.MM}) 
+      MoleFraction[2] Y = massToMoleFractions(state.X,{steam.MM,dryair.MM}) 
         "molar fraction";
    algorithm 
-     s := SingleGasNasa.s0_Tlow(dryair, state.T)*(1-state.X[Water])
+     s:=SingleGasNasa.s0_Tlow(dryair, state.T)*(1-state.X[Water])
        + SingleGasNasa.s0_Tlow(steam, state.T)*state.X[Water]
-       - gasConstant(state)*Modelica.Math.log(state.p/reference_p)
-       + sum(if Y[i] > Modelica.Constants.eps then -Y[i]*Modelica.Math.log(Y[i]) else 
-                   Y[i] for i in 1:size(Y,1));
+       - (state.X[Water]*Modelica.Constants.R/MMX[Water]*(if state.X[Water]<Modelica.Constants.eps then state.X[Water] else Modelica.Math.log(Y[Water]*state.p/reference_p))
+         + (1-state.X[Water])*Modelica.Constants.R/MMX[Air]*(if (1-state.X[Water])<Modelica.Constants.eps then (1-state.X[Water]) else Modelica.Math.log(Y[Air]*state.p/reference_p)));
    end specificEntropy;
     
@@ -1050 +1049 @@
         
         //trigger events
-        pd[i] = medium_T[i].Xi[1]*medium_T[i].MM/medium_T[i].MMX[1]*p_const;
+        pd[i] = medium_T[i].Xi[1]*medium_T[i].MM/MMX[1]*p_const;
         fog[i] = pd[i] >= Medium.saturationPressure(T_const[i]);
       end for;

Modelica/trunk/Modelica/Media/IdealGases/Common/package.mo

@@ -918 +918 @@
   redeclare function extends specificEntropy "Return specific entropy" 
     extends Modelica.Icons.Function;
-  algorithm 
-    s := s_TX(state.T, state.X) - gasConstant(state)*Modelica.Math.log(state.p/reference_p)
-      + MixEntropy(massToMoleFractions(state.X,data.MM));
+  protected 
+    Real[nX] Y(unit="mol/mol")=massToMoleFractions(state.X, data.MM) 
+      "Molar fractions";
+  algorithm 
+     s := s_TX(state.T, state.X) - sum(state.X[i]*Modelica.Constants.R/MMX[i]*
+      (if Y[i]>=Modelica.Constants.eps then Modelica.Math.log(Y[i]*state.p/
+      reference_p) else Y[i]) for i in 1:nX);
+    
   end specificEntropy;