Adding a test getPressure in PengRobinsonMFTP_Test.cpp file

test/thermo/PengRobinsonMFTP_Test.cpp

@@ -166,4 +166,34 @@ TEST_F(PengRobinsonMFTP_Test, setTP)
     }
 }
 
+TEST_F(PengRobinsonMFTP_Test, getPressure)
+{
+	// Check to make sure that the P-R equation is accurately reproduced for a few selected values
+
+	double a_coeff = 3.958134E+5;
+	double b_coeff = 26.6275/1000;
+	double acc_factor = 0.228;
+	double pres_theoretical, kappa, alpha, mv;
+	const double Tcrit = test_phase->critTemperature();
+
+	//Calculate kappa value
+	if (acc_factor <= 0.491) {
+		kappa = 0.37464 + 1.54226*acc_factor - 0.26992*acc_factor*acc_factor;
+	}
+	else {
+		kappa = 0.379642 + 1.487503*acc_factor - 0.164423*acc_factor*acc_factor + 0.016666*pow(acc_factor,3);
+	}
+
+	for (int i = 0; i<10; ++i)
+	{
+		const double temp = 294 + i * 2;
+		set_r(0.99);		
+		test_phase->setState_TR(temp, 1.0737);
+		mv = 1 / 1.0737 * test_phase->meanMolecularWeight();
+		//Calculate pressure using Peng-Robinson EoS
+		alpha = pow(1 + kappa*(1 - sqrt(temp / Tcrit)), 2);
+		pres_theoretical = GasConstant*temp / (mv - b_coeff) - a_coeff*alpha / (mv*mv + 2*b_coeff*mv - b_coeff*b_coeff);
+		EXPECT_NEAR(test_phase->pressure(), pres_theoretical, 10);
+	}
+}
 };