[Thermo] Fix pure fluid thermal expansion coefficient calculation

Cantera · Oct 19, 2016 · b1a1ce6 · b1a1ce6
1 parent f6df8f3
commit b1a1ce6
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Showing 2 changed files with 16 additions and 1 deletion.
diff --git a/interfaces/cython/cantera/test/test_purefluid.py b/interfaces/cython/cantera/test/test_purefluid.py
@@ -105,6 +105,21 @@ def test_properties_near_max(self):
         self.check_fd_properties(self.water.max_temp*(1-1e-5), 101325,
                                  self.water.max_temp*(1-1e-4), 101325, 1e-2)
 
+    def test_isothermal_compressibility_lowP(self):
+        # Low-pressure limit corresponds to ideal gas
+        ref = ct.Solution('gri30.xml')
+        ref.TPX = 450, 12, 'H2O:1.0'
+        self.water.TP = 450, 12
+        self.assertNear(ref.isothermal_compressibility,
+                        self.water.isothermal_compressibility, 1e-5)
+
+    def test_thermal_expansion_coeff_lowP(self):
+        # Low-pressure limit corresponds to ideal gas
+        ref = ct.Solution('gri30.xml')
+        ref.TPX = 450, 12, 'H2O:1.0'
+        self.water.TP = 450, 12
+        self.assertNear(ref.thermal_expansion_coeff,
+                        self.water.thermal_expansion_coeff, 1e-5)
     def test_TPX(self):
         self.water.TX = 400, 0.8
         T,P,X = self.water.TPX

diff --git a/src/tpx/Sub.cpp b/src/tpx/Sub.cpp
@@ -90,7 +90,7 @@ double Substance::thermalExpansionCoeff()
     Set(PropertyPair::TP, T2, p0);
     double v2 = v();
     Set(PropertyPair::TP, Tsave, p0);
-    return (v2 - v1)/((v2 + v1)*(T2-T1));
+    return 2.0*(v2 - v1)/((v2 + v1)*(T2-T1));
 }
 
 double Substance::isothermalCompressibility()