title	Getting Started with NeqSim in Java
description	Complete guide to using and developing with NeqSim in Java — prerequisites, installation, first calculations, process simulation, and developer setup.

Getting Started with NeqSim in Java

This guide covers everything you need to start using NeqSim as a Java library — from installing prerequisites to running your first thermodynamic calculation and building a process simulation.

Prerequisites

Tool	Version	Purpose
JDK	8 or newer (11+ recommended)	Compile and run NeqSim
Maven	3.6+	Dependency management (included via wrapper if building from source)
Git	Any recent	Clone the repository (only needed for development)
IDE (optional)	IntelliJ IDEA, Eclipse, or VS Code	Recommended for development

Installing a JDK

If you don't have a JDK installed:

Windows: Download Eclipse Temurin or Oracle JDK
macOS: brew install temurin or download from Adoptium
Linux: sudo apt install openjdk-11-jdk (Ubuntu/Debian) or sudo yum install java-11-openjdk-devel (RHEL/CentOS)

Verify your installation:

java -version
# Should show: openjdk version "11.0.x" or similar

Using NeqSim as a library

The easiest way to use NeqSim is to add it as a Maven dependency to your project.

Option 1: Maven Central (recommended)

No authentication required. Add to your pom.xml:

<dependency>
  <groupId>com.equinor.neqsim</groupId>
  <artifactId>neqsim</artifactId>
  <version>3.6.1</version>
</dependency>

Run mvn clean install and Maven will resolve NeqSim from Central automatically.

Option 2: GitHub Packages (latest snapshots)

Useful if you want pre-release versions.

Create a Personal Access Token with read:packages scope.
Add to your Maven settings.xml (typically at ~/.m2/settings.xml):

<settings>
  <servers>
    <server>
      <id>github</id>
      <username>YOUR_GITHUB_USERNAME</username>
      <password>YOUR_GITHUB_TOKEN</password>
    </server>
  </servers>
</settings>

Add the repository and dependency to pom.xml:

<repositories>
  <repository>
    <id>github</id>
    <url>https://maven.pkg.github.com/equinor/neqsim</url>
  </repository>
</repositories>

<dependency>
  <groupId>com.equinor.neqsim</groupId>
  <artifactId>neqsim</artifactId>
  <version>3.6.1</version>
</dependency>

Option 3: Direct JAR download

Download neqsim-x.x.x.jar from the releases page and add it to your classpath.

Your first calculation — TP flash

This example creates a natural gas mixture and calculates its phase equilibrium and physical properties:

import neqsim.thermo.system.SystemSrkEos;
import neqsim.thermodynamicoperations.ThermodynamicOperations;

public class FirstCalculation {
    public static void main(String[] args) {
        // 1. Create fluid at 25°C and 50 bara
        SystemSrkEos fluid = new SystemSrkEos(273.15 + 25.0, 50.0);
        fluid.addComponent("methane", 0.90);
        fluid.addComponent("ethane", 0.06);
        fluid.addComponent("propane", 0.03);
        fluid.addComponent("n-butane", 0.01);
        fluid.setMixingRule("classic");  // ALWAYS set a mixing rule

        // 2. Run flash calculation
        ThermodynamicOperations ops = new ThermodynamicOperations(fluid);
        ops.TPflash();

        // 3. Initialize physical properties (REQUIRED before reading density, viscosity, etc.)
        fluid.initProperties();

        // 4. Read results
        System.out.println("Phases:       " + fluid.getNumberOfPhases());
        System.out.println("Density:      " + fluid.getDensity("kg/m3") + " kg/m³");
        System.out.println("Z-factor:     " + fluid.getPhase("gas").getZ());
        System.out.println("Viscosity:    " + fluid.getPhase("gas").getViscosity("kg/msec") + " kg/(m·s)");
        System.out.println("Molar mass:   " + fluid.getMolarMass("kg/mol") * 1000.0 + " g/mol");
    }
}

Key pattern to remember

Create fluid → Add components → Set mixing rule → Flash → initProperties() → Read results

Important: Always call fluid.initProperties() after a flash calculation before reading transport properties (density, viscosity, thermal conductivity). The flash itself only solves phase equilibrium — transport properties require the extra initialization step.

Process simulation

Build a flowsheet by chaining equipment together:

import neqsim.thermo.system.SystemSrkEos;
import neqsim.process.equipment.stream.Stream;
import neqsim.process.equipment.separator.Separator;
import neqsim.process.equipment.compressor.Compressor;
import neqsim.process.equipment.heatexchanger.Cooler;
import neqsim.process.processmodel.ProcessSystem;

public class SimpleProcess {
    public static void main(String[] args) {
        // Create fluid
        SystemSrkEos fluid = new SystemSrkEos(273.15 + 30.0, 80.0);
        fluid.addComponent("methane", 0.80);
        fluid.addComponent("ethane", 0.12);
        fluid.addComponent("propane", 0.05);
        fluid.addComponent("n-butane", 0.03);
        fluid.setMixingRule("classic");

        // Build flowsheet
        Stream feed = new Stream("Feed", fluid);
        feed.setFlowRate(50000.0, "kg/hr");

        Separator separator = new Separator("HP Separator", feed);

        Compressor compressor = new Compressor("Compressor", separator.getGasOutStream());
        compressor.setOutletPressure(150.0);

        Cooler aftercooler = new Cooler("Aftercooler", compressor.getOutletStream());
        aftercooler.setOutTemperature(273.15 + 30.0);

        // Assemble and run
        ProcessSystem process = new ProcessSystem();
        process.add(feed);
        process.add(separator);
        process.add(compressor);
        process.add(aftercooler);
        process.run();

        // Results
        System.out.println("Compressor power:   " + compressor.getPower("kW") + " kW");
        System.out.println("Outlet temperature: " + (compressor.getOutletStream().getTemperature() - 273.15) + " °C");
        System.out.println("Cooling duty:       " + aftercooler.getDuty() / 1000.0 + " kW");
    }
}

Available equipment types

Category	Equipment classes
Separation	`Separator`, `ThreePhaseSeparator`, `DistillationColumn`, `MembraneSeparator`, `ComponentSplitter`
Compression	`Compressor`, `Pump`, `Expander`, `Ejector`
Heat transfer	`Heater`, `Cooler`, `HeatExchanger`
Flow control	`ThrottlingValve`, `Splitter`, `Mixer`
Pipelines	`PipeBeggsAndBrills`, `AdiabaticPipe`
Reactors	`GibbsReactor`
Utilities	`Recycle`, `Adjuster`, `SetPoint`

Choosing an equation of state

EOS class	Best for	Notes
`SystemSrkEos`	General hydrocarbon systems	Good all-round choice
`SystemPrEos`	Reservoir fluids, liquid density	Better liquid density than SRK
`SystemSrkCPAstatoil`	Water, glycols, alcohols, amines	Handles hydrogen bonding (CPA)
`SystemGERG2008Eos`	Natural gas custody transfer	Highest accuracy for gas properties
`SystemUMRPRUMCEos`	Wide-range mixtures	Predictive, no interaction parameters needed

// SRK for general use
SystemSrkEos gas = new SystemSrkEos(298.15, 50.0);

// PR for oil systems
SystemPrEos oil = new SystemPrEos(350.0, 200.0);

// CPA for water/glycol systems
SystemSrkCPAstatoil wet = new SystemSrkCPAstatoil(280.0, 60.0);
wet.addComponent("methane", 0.90);
wet.addComponent("water", 0.10);
wet.setMixingRule(10);  // CPA mixing rule

Common flash calculations

ThermodynamicOperations ops = new ThermodynamicOperations(fluid);

ops.TPflash();                          // Temperature-pressure flash
ops.PHflash(enthalpy, 0);              // Pressure-enthalpy flash
ops.PSflash(entropy);                   // Pressure-entropy flash
ops.dewPointTemperatureFlash();         // Dew point temperature
ops.bubblePointPressureFlash(false);    // Bubble point pressure
ops.hydrateFormationTemperature();      // Hydrate formation temperature
ops.calcPTphaseEnvelope();              // Full phase envelope

Developing NeqSim — building from source

Clone and build

git clone https://github.com/equinor/neqsim.git
cd neqsim
./mvnw install        # Linux/macOS
mvnw.cmd install      # Windows

The Maven wrapper (mvnw/mvnw.cmd) downloads the correct Maven version automatically — no separate Maven installation needed.

Run tests

./mvnw test                                      # all tests
./mvnw test -Dtest=SeparatorTest                 # single class
./mvnw test -Dtest=SeparatorTest#testTwoPhase    # single method

Static analysis

./mvnw checkstyle:check     # code style
./mvnw spotbugs:check       # bug detection
./mvnw pmd:check            # code quality

Code coverage

./mvnw jacoco:prepare-agent test install jacoco:report
# Report at target/site/jacoco/index.html

VS Code with dev container

The repository includes a ready-to-use dev container with Maven and recommended extensions pre-installed:

git clone https://github.com/equinor/neqsim.git
cd neqsim
code .   # VS Code will prompt to reopen in container

IntelliJ IDEA

Open IntelliJ IDEA
File → Open → select the cloned neqsim folder
IntelliJ auto-detects the Maven project and imports dependencies
Wait for indexing to complete
Right-click any test class → Run to verify the setup

Eclipse

File → Import → Maven → Existing Maven Projects
Browse to the cloned neqsim folder
Select pom.xml and finish the import
Right-click the project → Maven → Update Project

Project structure

src/
  main/java/neqsim/
    thermo/                  Thermodynamic models (60+ EOS classes)
    thermodynamicoperations/ Flash calculations (TP, PH, PS, dew, bubble, phase envelope)
    physicalproperties/      Transport properties (viscosity, conductivity, diffusion)
    process/
      equipment/             33+ unit operations (separator, compressor, HX, valve, ...)
      processmodel/          ProcessSystem — the flowsheet orchestrator
      mechanicaldesign/      Wall thickness, cost estimation, ASME/API/DNV standards
      measurementdevice/     Transmitters, meters, monitors
      controllerdevice/      PID and advanced controllers
    pvtsimulation/           PVT lab experiments (CME, CVD, DL, swelling, ...)
    standards/               Gas quality (ISO 6976), oil quality, sales contracts
    fluidmechanics/          Pipeline hydraulics
    chemicalreactions/       Reaction equilibrium and kinetics
    statistics/              Parameter fitting, regression
  test/java/neqsim/         JUnit 5 tests (mirrors production structure)
  main/resources/            Component databases, design data CSVs

Key conventions for contributors

Java 8 compatibility — All code must compile with Java 8. Do not use var, List.of(), Map.of(), text blocks, records, or other Java 9+ features.
Mixing rule required — Always call setMixingRule() after adding components.
initProperties() after flash — Call fluid.initProperties() before reading transport properties.
Tests required — All new code must have JUnit 5 tests. All tests must pass before merging.
Checkstyle — Code must pass ./mvnw checkstyle:check (Google style with project overrides).

Next steps

NeqSim User Documentation — Full docs site
JavaDoc API Reference — Complete API docs
Java Wiki & examples — Usage patterns and guides
Jupyter notebooks — 30+ runnable examples
NeqSim Colab demo — Try NeqSim interactively
GitHub Discussions — Ask questions
CONTRIBUTING.md — How to contribute

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Getting Started with NeqSim in Java

Prerequisites

Installing a JDK

Using NeqSim as a library

Option 1: Maven Central (recommended)

Option 2: GitHub Packages (latest snapshots)

Option 3: Direct JAR download

Your first calculation — TP flash

Key pattern to remember

Process simulation

Available equipment types

Choosing an equation of state

Common flash calculations

Developing NeqSim — building from source

Clone and build

Run tests

Static analysis

Code coverage

VS Code with dev container

IntelliJ IDEA

Eclipse

Project structure

Key conventions for contributors

Next steps

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Getting Started with NeqSim in Java

Prerequisites

Installing a JDK

Using NeqSim as a library

Option 1: Maven Central (recommended)

Option 2: GitHub Packages (latest snapshots)

Option 3: Direct JAR download

Your first calculation — TP flash

Key pattern to remember

Process simulation

Available equipment types

Choosing an equation of state

Common flash calculations

Developing NeqSim — building from source

Clone and build

Run tests

Static analysis

Code coverage

VS Code with dev container

IntelliJ IDEA

Eclipse

Project structure

Key conventions for contributors

Next steps