Java Quickstart

Get NeqSim running in a Java project with one thermodynamic calculation and one composable process simulation. The examples use NeqSim 3.18.0; check Maven Central for a newer published version before starting a new project.

Step 1: add NeqSim to a project

Add the dependency to your pom.xml:

<dependency>
  <groupId>com.equinor.neqsim</groupId>
  <artifactId>neqsim</artifactId>
  <version>3.18.0</version>
</dependency>

The run command below uses Maven’s exec plugin. Add this build entry if the project does not already configure it:

<build>
  <plugins>
    <plugin>
      <groupId>org.codehaus.mojo</groupId>
      <artifactId>exec-maven-plugin</artifactId>
      <version>3.6.3</version>
    </plugin>
  </plugins>
</build>

With Gradle:

implementation 'com.equinor.neqsim:neqsim:3.18.0'

Step 2: first flash calculation

Create FirstCalculation.java:

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

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

    public static void main(String[] args) {
        // SystemSrkEos accepts temperature in K and absolute pressure in bara.
        SystemSrkEos fluid = new SystemSrkEos(298.15, 50.0);

        // addComponent accepts component amounts in mol. These sum to 1.0 mol,
        // so the amounts are also the overall mole fractions for this example.
        fluid.addComponent("methane", 0.85);
        fluid.addComponent("ethane", 0.10);
        fluid.addComponent("propane", 0.05);

        // Select an appropriate mixing rule before flashing a cubic-EOS mixture.
        fluid.setMixingRule("classic");

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

        // Initialize physical properties before reading density or transport properties.
        fluid.initProperties();

        logger.info("Number of phases: {}", fluid.getNumberOfPhases());
        logger.info("Bulk density: {} kg/m³", fluid.getDensity("kg/m3"));
        logger.info("System Z-factor: {}", fluid.getZ());
    }
}

The API unit token is "kg/m3"; the displayed SI symbol is kg/m³. getDensity("kg/m3") converts the returned unit but does not select or validate a density model.

Run it from the project directory:

mvn compile exec:java -Dexec.mainClass="FirstCalculation"

Step 3: first process simulation

Create FirstProcess.java:

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import neqsim.process.equipment.compressor.Compressor;
import neqsim.process.equipment.separator.Separator;
import neqsim.process.equipment.stream.Stream;
import neqsim.process.processmodel.ProcessSystem;
import neqsim.thermo.system.SystemSrkEos;

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

    public static void main(String[] args) {
        SystemSrkEos fluid = new SystemSrkEos(273.15 + 30.0, 50.0);
        fluid.addComponent("methane", 0.70);
        fluid.addComponent("ethane", 0.10);
        fluid.addComponent("propane", 0.10);
        fluid.addComponent("n-butane", 0.05);
        fluid.addComponent("n-pentane", 0.05);
        fluid.setMixingRule("classic");

        ProcessSystem process = new ProcessSystem();

        Stream feed = new Stream("Feed", fluid);
        feed.setFlowRate(10000.0, "kg/hr");
        process.add(feed);

        // Separator performs an equilibrium split at the feed state, here 50 bara.
        Separator separator = new Separator("HP Separator", feed);
        separator.setInternalDiameter(2.0);
        process.add(separator);

        Compressor compressor =
            new Compressor("Gas Compressor", separator.getGasOutStream());
        compressor.setOutletPressure(80.0, "bara");
        compressor.setIsentropicEfficiency(0.75);
        process.add(compressor);

        process.run();

        double gasFlowKgPerHour =
            separator.getGasOutStream().getFlowRate("kg/hr");
        double liquidFlowKgPerHour =
            separator.getLiquidOutStream().getFlowRate("kg/hr");

        logger.info("Gas outlet: {} kg/hr", gasFlowKgPerHour);
        logger.info("Liquid outlet: {} kg/hr", liquidFlowKgPerHour);
        logger.info("Separated total: {} kg/hr", gasFlowKgPerHour + liquidFlowKgPerHour);
        logger.info("Compressor power: {} kW", compressor.getPower("kW"));
        logger.info(
            "Compressor outlet temperature: {} °C",
            compressor.getOutletStream().getTemperature("C"));
    }
}

A Separator does not impose a pressure reduction. Add a valve or another pressure-changing unit upstream when the engineering case requires letdown before separation. The stream, separator, compressor, and ProcessSystem remain available for extension into a larger flowsheet.

Common gotchas

Issue Corrective action
NullPointerException or unavailable physical properties Call fluid.initProperties() after the flash before reading density, viscosity, or conductivity.
Unexpected density Request an explicit supported unit and verify the selected thermodynamic model, volume-correction setting, composition, temperature, and pressure. The unit string alone does not enable Peneloux correction.
Temperature seems wrong Constructors use K unless an API explicitly accepts a unit. Convert with T_K = T_C + 273.15 or use a setter with a unit argument.
Pressure basis is unclear Constructors and single-argument process pressure setters use bara. Prefer overloads such as setOutletPressure(80.0, "bara") in user examples.
Mixing rule is missing Select the mixing rule appropriate to the chosen model and mixture before the first flash. "classic" is the simple cubic-EOS choice used here.
Separator pressure is unexpected A separator uses its inlet state; it does not perform an implicit letdown. Model pressure-changing equipment explicitly.
Flash does not converge Verify component names, positive amounts, units, model applicability, and a physically plausible temperature-pressure state. Let the exception propagate while diagnosing it.

Engineering boundary

These examples demonstrate API composition and deterministic calculations, not fluid-model selection, equipment sizing, process design approval, or safety certification. Validate the model, composition, operating envelope, convergence, conservation, and results against suitable engineering evidence before design use.

Next steps

API quick reference

Key interfaces to explore in the JavaDoc:

Interface Purpose
SystemInterface Fluid composition, properties, and flash state
PhaseInterface Individual phase properties
ComponentInterface Pure-component and in-mixture properties
ProcessEquipmentInterface Common process-equipment contract
StreamInterface Composable material streams