Fix issues with isothermal compressibility and thermal expansion coefficient

Fixed return type of `RedlichKwongMFTP` functions
Fixed sign errors in `PengRobinson` and `RedlichKwongMFTP` derivations

Author: corykinney

src/thermo/PengRobinson.cpp

@@ -643,7 +643,7 @@ double PengRobinson::isothermalCompressibility() const
 
     double dAdP = A / P;
     double dBdP = B / P;
-    double dZdP = ((Z * Z + 3 * B * B + 2 * B - A - 2 * Z * (3 * B + 1)) * dBdP + (Z - B) * dAdP) /
+    double dZdP = ((B - Z) * dAdP + (A - 2 * B - 3 * B * B + 2 * Z + 6 * B * Z - Z * Z) * dBdP) /
         (3 * Z * Z + 2 * Z * (B - 1) + A - 2 * B - 3 * B * B);
 
     return 1 / P - dZdP / Z;
@@ -662,10 +662,10 @@ double PengRobinson::thermalExpansionCoeff() const
 
     double dAdT = P / (RT_ * RT_) * (daAlpha_dT() - 2 * m_aAlpha_mix / T);
     double dBdT = -B / T;
-    double dZdT = ((Z * Z + 3 * B * B + 2 * B - A - 2 * Z * (3 * B + 1)) * dBdT + (Z - B) * dAdT) /
+    double dZdT = ((B - Z) * dAdT + (A - 2 * B - 3 * B * B + 2 * Z + 6 * B * Z - Z * Z) * dBdT) /
         (3 * Z * Z + 2 * Z * (B - 1) + A - 2 * B - 3 * B * B);
 
-    return -1 / T - dZdT / Z;
+    return 1 / T + dZdT / Z;
 }
 
 void PengRobinson::calculatePressureDerivatives() const

src/thermo/RedlichKwongMFTP.cpp

@@ -707,7 +707,7 @@ doublereal RedlichKwongMFTP::dpdVCalc(doublereal TKelvin, doublereal molarVol, d
     return dpdv;
 }
 
-void RedlichKwongMFTP::isothermalCompressibility() const
+double RedlichKwongMFTP::isothermalCompressibility() const
 {
     double P = pressure();
     double mv = molarVolume();
@@ -725,7 +725,7 @@ void RedlichKwongMFTP::isothermalCompressibility() const
     return 1 / P - dZdP / Z;
 }
 
-void RedlichKwongMFTP::thermalExpansionCoeff() const
+double RedlichKwongMFTP::thermalExpansionCoeff() const
 {
     double P = pressure();
     double mv = molarVolume();
@@ -740,7 +740,7 @@ void RedlichKwongMFTP::thermalExpansionCoeff() const
     double dBdT = -B / T;
     double dZdT = ((B - Z) * dAdT + (A + Z + 2 * B * Z) * dBdT) / (3 * Z * Z - 2 * Z + A - B - B * B);
 
-    return - 1 / T - dZdT / Z;
+    return 1 / T + dZdT / Z;
 }
 
 void RedlichKwongMFTP::pressureDerivatives() const