[Thermo] Correct RedlichKwong::getPartialMolarIntEnergies

Fixes #998
Cantera · Mar 15, 2022 · c72f095 · c72f095
1 parent b7f40b2
commit c72f095
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Showing 2 changed files with 25 additions and 2 deletions.
diff --git a/src/thermo/RedlichKwongMFTP.cpp b/src/thermo/RedlichKwongMFTP.cpp
@@ -337,8 +337,13 @@ void RedlichKwongMFTP::getPartialMolarEntropies(doublereal* sbar) const
 
 void RedlichKwongMFTP::getPartialMolarIntEnergies(doublereal* ubar) const
 {
-    getIntEnergy_RT(ubar);
-    scale(ubar, ubar+m_kk, ubar, RT());
+    // u_k = h_k - P * v_k
+    getPartialMolarVolumes(m_partialMolarVolumes.data());
+    getPartialMolarEnthalpies(ubar);
+    double p = pressure();
+    for (size_t k = 0; k < nSpecies(); k++) {
+        ubar[k] -= p * m_partialMolarVolumes[k];
+    }
 }
 
 void RedlichKwongMFTP::getPartialMolarVolumes(doublereal* vbar) const

diff --git a/test/thermo/RedlichKwongMFTP_Test.cpp b/test/thermo/RedlichKwongMFTP_Test.cpp
@@ -204,4 +204,22 @@ TEST_F(RedlichKwongMFTP_Test, localCritProperties)
     EXPECT_NEAR(test_phase->critPressure(), 22.064e6, 1e-4);
 }
 
+TEST_F(RedlichKwongMFTP_Test, partialMolarIntEnergy)
+{
+    // Check that sum(X_k * u) = u
+    set_r(0.4);
+    test_phase->setState_TP(400, 1.3e7);
+    double u_ref = test_phase->intEnergy_mole();
+    size_t kk = test_phase->nSpecies();
+    vector_fp uk(kk);
+    vector_fp X(kk);
+    test_phase->getMoleFractions(X.data());
+    test_phase->getPartialMolarIntEnergies(uk.data());
+    double u_test = 0;
+    for (size_t k = 0; k < kk; k++) {
+        u_test += uk[k] * X[k];
+    }
+    EXPECT_NEAR(u_ref, u_test, 1e-13 * std::abs(u_ref));
+}
+
 };