ThermodynamicOperations solves equilibrium and state-function specifications for a configured SystemInterface. A reliable workflow is:

  1. define the fluid and mixing rule;
  2. set the known state variables;
  3. run the appropriate flash;
  4. call initProperties() before reading density or transport properties; and
  5. check that the resulting phases and engineering values are physical.

Complete Java quick start

This Java 8 program performs a TP flash at 25 °C and 50 bara, initializes properties, and then calculates the state after an isenthalpic pressure reduction to 30 bara.

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;
import neqsim.thermodynamicoperations.ThermodynamicOperations;

public final class ThermodynamicOperationsQuickStart {
  private static final Logger logger =
      LogManager.getLogger(ThermodynamicOperationsQuickStart.class);

  private ThermodynamicOperationsQuickStart() {}

  public static void main(String[] args) {
    SystemInterface fluid = new SystemSrkEos(298.15, 50.0);
    fluid.addComponent("methane", 0.90);
    fluid.addComponent("ethane", 0.07);
    fluid.addComponent("propane", 0.03);
    fluid.setMixingRule("classic");

    ThermodynamicOperations operations = new ThermodynamicOperations(fluid);
    operations.TPflash();
    fluid.initProperties();

    if (!fluid.hasPhaseType("gas")) {
      throw new IllegalStateException("Expected a gas phase after the TP flash");
    }
    double vaporFraction = fluid.getPhaseFraction("gas", "mole");
    double inletDensity = fluid.getDensity("kg/m3");
    double inletEnthalpy = fluid.getEnthalpy();

    fluid.setPressure(30.0, "bara");
    operations.PHflash(inletEnthalpy);
    fluid.initProperties();

    logger.info("Inlet gas fraction: {} mol/mol", vaporFraction);
    logger.info("Inlet density: {} kg/m3", inletDensity);
    logger.info("Outlet temperature: {} C", fluid.getTemperature("C"));
    logger.info("Enthalpy residual: {} J", fluid.getEnthalpy() - inletEnthalpy);
  }
}

For this lean-gas case, the focused documentation regression requires a gas fraction above 0.999 mol/mol, an inlet density between 35 and 50 kg/m³, a finite outlet temperature, and isenthalpic closure within 0.001 J. These are deliberately bounded engineering checks rather than portable exact output values.

Choose the flash from the specification

Operation Known state Solved state Typical use
TPflash() temperature and pressure phase amounts and compositions separator or pipeline state
PHflash(H) pressure and total enthalpy temperature and phase equilibrium valve, heater, or heat exchanger
PSflash(S) pressure and total entropy temperature and phase equilibrium ideal compressor or expander reference
TVflash(V, "m3") temperature and total volume pressure and phase equilibrium fixed-volume screening
VUflash(V, u, "m3", "J/kg") total volume and specific internal energy temperature, pressure, and phases dynamic vessel calculations

The no-unit PHflash and PSflash overloads use total system enthalpy and entropy in NeqSim’s internal SI representation. Prefer supported explicit unit strings when values originate outside NeqSim. A total-volume specification belongs to the fluid inventory from which it was calculated, so preserve the system’s material amount when copying it between states.

Property initialization boundary

A flash establishes the equilibrium state. It does not guarantee that all transport-property models have been evaluated. Call initProperties() after the flash before retrieving density, viscosity, thermal conductivity, or interfacial tension.

Use bulk getters such as fluid.getDensity("kg/m3") only when a bulk value is meaningful. For multiphase systems, check phase existence and retrieve a named phase explicitly, for example fluid.getPhase("gas").getDensity("kg/m3").

Do not use init(3) as a replacement for a flash after changing temperature, pressure, or composition. The flash operation establishes the new equilibrium; initProperties() then initializes thermodynamic and physical properties for the accepted state.

Specialized equilibrium workflows

The compact quick start above covers state flashes. Use the dedicated guides for operations that need additional phase configuration, model selection, or result extraction:

There is no generic electrolyteFlash(), calcChemicalEquilibrium(), or calcSolidFormationTemperature() method on ThermodynamicOperations. Select the documented operation for the physical problem instead of relying on those legacy names.

Reuse and independent calculations

Reuse one ThermodynamicOperations instance while changing the state of the same fluid. Clone the fluid and construct a separate operations object when two calculations must remain independent. Always validate phase existence, conservation, units, and convergence before using a result in an engineering decision.