Thermodynamic Workflows

Use these recipes to configure fluids and run equilibrium calculations with NeqSim. The Java snippets mirror the workflow used in other language bindings.

1. Build a Fluid

SystemInterface fluid = new SystemPrEos(313.15, 80.0);
fluid.addComponent("methane", 0.85);
fluid.addComponent("ethane", 0.05);
fluid.addTBPfraction("C7+", 0.10, 0.45, 8.0); // name, moles, density [g/cc], MW
fluid.createDatabase(true); // enable access to component data
fluid.setMixingRule(1); // classical van der Waals mixing rule
fluid.init(0);

Tips:

• Always call createDatabase(true) before adding TBP fractions so critical properties and acentric factors are filled automatically.
• Use addPlusFraction for simpler heavy-end inputs, or addFluid to merge two existing systems.

2. Choose a Model and Mixing Rule

• setMixingRule(1): classical quadratic kij.
• setMixingRule(2): Huron–Vidal (gamma-phi) coupling.
• setMixingRule(4): Wong–Sandler (NRTL-based) coupling.
• setMixingRule(7): Simplified CPA cross-association rules.

For lean gas, start with PR and kij from correlations; for rich liquids or polar systems, move to SRK-Twu + Huron–Vidal or CPA-SRK.

3. Run Thermodynamic Operations

Instantiate ThermodynamicOperations with the configured fluid to access flash and envelope tools:

ThermodynamicOperations ops = new ThermodynamicOperations(fluid);
ops.TPflash();
fluid.initProperties();
System.out.println("Vapor fraction: " + fluid.getPhaseFraction(0));

Common operations include:

• PSflash(pressure, entropy), PHflash(pressure, enthalpy) for process simulators.
• dewPointTemperature(pressure) and bubblePointPressure(temperature) for PVT lab matches.
• calcPTphaseEnvelope() and calcPseudocriticalTemperature() for compositional screening.

4. Save and Reuse States

Export an EOS state to JSON or clone fluids when sweeping conditions:

SystemInterface clone = fluid.clone();
clone.setTemperature(280.0);
clone.setPressure(10.0);
new ThermodynamicOperations(clone).TPflash();

5. Debugging and Validation

• Call display() on the fluid to dump compositions, kij values, and phase properties.
• Use calcChemicalEquilibrium() after setting reaction stoichiometry to couple reactions into flashes.
• Compare getMolarMass() and getZ() against lab PVT data to verify characterization accuracy.