fixed bug in TPflash. Added TVflash test (#454)

Author: EvenSol

src/main/java/neqsim/thermodynamicOperations/flashOps/TPflash.java

@@ -166,6 +166,7 @@ public void setNewK() {
    * </p>
    */
   public void resetK() {
+    
     for (i = 0; i < system.getPhase(0).getNumberOfComponents(); i++) {
       lnK[i] = lnOldK[i];
       system.getPhase(0).getComponents()[i].setK(Math.exp(lnK[i]));
@@ -402,7 +403,7 @@ public void run() {
         gibbsEnergy = system.getGibbsEnergy();
 
         if ((gibbsEnergy - gibbsEnergyOld) / Math.abs(gibbsEnergyOld) > 1e-3
-            && !system.isChemicalSystem()) {
+            && !system.isChemicalSystem() && timeFromLastGibbsFail>0) {
           resetK();
           timeFromLastGibbsFail = 0;
           // logger.info("gibbs decrease " + (gibbsEnergy - gibbsEnergyOld) /

src/test/java/neqsim/thermodynamicOperations/flashOps/TVFlashTest.java

@@ -0,0 +1,72 @@
+/**
+ * 
+ */
+package neqsim.thermodynamicOperations.flashOps;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import neqsim.thermodynamicOperations.ThermodynamicOperations;
+
+/**
+ * @author ESOL
+ *
+ */
+class TVFlashTest {
+
+  static neqsim.thermo.system.SystemInterface testSystem = null;
+  static neqsim.thermo.system.SystemInterface testSystem2 = null;
+  static ThermodynamicOperations testOps = null;
+
+  /**
+   * @throws java.lang.Exception
+   */
+  @BeforeEach
+  void setUp() throws Exception {
+    testSystem = new neqsim.thermo.system.SystemUMRPRUMCEos(293.15, 0.1);
+    testSystem.addComponent("methane", 0.0);
+    testSystem.addComponent("ethane", 0.0);
+    testSystem.addComponent("n-pentane", 9E-1);
+    testSystem.addComponent("nC16", 1E-1);
+    testSystem.setMixingRule("classic");
+    testOps = new ThermodynamicOperations(testSystem);
+    testOps.TPflash();
+    testSystem.initProperties();
+    testSystem.setTotalFlowRate(1.0, "kg/sec");
+    testOps.TPflash();
+    testSystem.initProperties();
+    
+    testSystem2 = new neqsim.thermo.system.SystemUMRPRUMCEos(293.15, 0.1);
+    testSystem2.addComponent("methane", 8.5E-1);
+    testSystem2.addComponent("ethane", 1.5E-1);
+    testSystem2.addComponent("n-pentane", 0);
+    testSystem2.addComponent("nC16", 0);
+    testSystem2.setMixingRule("classic");
+    ThermodynamicOperations testOps = new ThermodynamicOperations(testSystem2);
+    testOps.TPflash();
+    testSystem2.initProperties();
+    testSystem2.setTotalFlowRate(0.3, "kg/sec");
+    testOps.TPflash();
+    testSystem2.initProperties();
+  }
+  
+  @Test
+  void testTVflash() {
+    double total_rig_volume = 0.998;
+    
+    for(int i=0;i<50;i++) {
+      testSystem.addFluid(testSystem2);
+      ThermodynamicOperations testOps = new ThermodynamicOperations(testSystem);
+      try {
+      testOps.TVflash(total_rig_volume, "m3");
+      }
+      catch(Exception e) {
+        System.out.println("error iterations " + i);
+        e.printStackTrace();
+      }
+   }
+    assertEquals(235263.80103781424, testSystem.getEnthalpy(), 1e-2);
+  }
+    
+  }
+