Thermo System Package

Documentation for fluid system implementations in NeqSim.

Table of Contents

Overview

Location: neqsim.thermo.system

The system package contains 58+ implementations of thermodynamic models, from simple ideal gas to complex associating equations of state.

System Hierarchy

SystemInterface
└── SystemThermo (abstract base)
    ├── SystemEos (cubic EoS base)
    │   ├── SystemSrkEos
    │   ├── SystemPrEos
    │   └── ...
    ├── SystemSrkCPA (CPA base)
    │   ├── SystemSrkCPAstatoil
    │   └── ...
    └── SystemPCSAFT (SAFT base)
        └── ...

Cubic Equations of State

Soave-Redlich-Kwong (SRK)

import neqsim.thermo.system.SystemSrkEos;

SystemSrkEos fluid = new SystemSrkEos(298.15, 50.0);
fluid.addComponent("methane", 1.0);
fluid.setMixingRule("classic");
\[P = \frac{RT}{V-b} - \frac{a\alpha(T)}{V(V+b)}\]

Peng-Robinson (PR)

import neqsim.thermo.system.SystemPrEos;

SystemPrEos fluid = new SystemPrEos(298.15, 50.0);
fluid.addComponent("methane", 1.0);
fluid.setMixingRule("classic");
\[P = \frac{RT}{V-b} - \frac{a\alpha(T)}{V(V+b)+b(V-b)}\]

Available Cubic EoS Classes

Class Description
SystemSrkEos Standard SRK
SystemPrEos Standard PR
SystemSrkMathiasCopeman SRK with Mathias-Copeman alpha
SystemPrMathiasCopeman PR with Mathias-Copeman alpha
SystemSrkSchwartzentruberRenon SRK with GE mixing
SystemPrSchwartzentruberRenon PR with GE mixing
SystemSrkTwuCoon SRK with Twu-Coon alpha
SystemPrTwuCoon PR with Twu-Coon alpha
SystemPrDanesh PR with Danesh modifications

Alpha Function Options

// Standard Soave alpha
SystemSrkEos std = new SystemSrkEos(T, P);

// Mathias-Copeman alpha (better for polar)
SystemSrkMathiasCopeman mc = new SystemSrkMathiasCopeman(T, P);

// Twu-Coon alpha
SystemSrkTwuCoon tc = new SystemSrkTwuCoon(T, P);

Association Equations

CPA (Cubic-Plus-Association)

For systems with hydrogen bonding (water, alcohols, glycols, amines).

import neqsim.thermo.system.SystemSrkCPAstatoil;

SystemSrkCPAstatoil fluid = new SystemSrkCPAstatoil(298.15, 10.0);
fluid.addComponent("water", 1.0);
fluid.addComponent("methane", 2.0);
fluid.setMixingRule(10);  // CPA mixing rule

Available CPA Classes

Class Description
SystemSrkCPAstatoil SRK-CPA (Equinor parameters)
SystemPrCPA PR-CPA
SystemSrkCPA SRK-CPA (generic)
SystemElectrolyteCPA CPA with electrolytes

CPA Mixing Rules

// Standard CPA mixing rule
fluid.setMixingRule(10);

// With cross-association
fluid.setMixingRule(10);

SAFT-Based EoS

PC-SAFT

Statistical Associating Fluid Theory with perturbed chain.

import neqsim.thermo.system.SystemPCSAFT;

SystemPCSAFT fluid = new SystemPCSAFT(298.15, 10.0);
fluid.addComponent("methane", 1.0);
fluid.addComponent("n-hexane", 0.5);
fluid.setMixingRule("classic");

ePCSAFT (Electrolyte PC-SAFT)

import neqsim.thermo.system.SystemElectrolytePCSAFT;

SystemElectrolytePCSAFT brine = new SystemElectrolytePCSAFT(298.15, 1.0);
brine.addComponent("water", 1.0);
brine.addComponent("Na+", 0.1);
brine.addComponent("Cl-", 0.1);

Activity Models

NRTL

import neqsim.thermo.system.SystemNRTL;

SystemNRTL liquid = new SystemNRTL(298.15, 1.0);
liquid.addComponent("ethanol", 0.5);
liquid.addComponent("water", 0.5);

UNIFAC

import neqsim.thermo.system.SystemUNIFAC;

SystemUNIFAC liquid = new SystemUNIFAC(298.15, 1.0);
liquid.addComponent("acetone", 0.5);
liquid.addComponent("water", 0.5);

EoS/GE Combinations

// SRK with UNIFAC for liquid
SystemSrkSchwartzentruberRenon fluid = new SystemSrkSchwartzentruberRenon(T, P);

Reference EoS

GERG-2008

High-accuracy reference equation for natural gas.

import neqsim.thermo.system.SystemGERG2008;

SystemGERG2008 gas = new SystemGERG2008(288.15, 50.0);
gas.addComponent("nitrogen", 0.02);
gas.addComponent("CO2", 0.01);
gas.addComponent("methane", 0.85);
gas.addComponent("ethane", 0.08);
gas.addComponent("propane", 0.04);

Accuracy:

UMR-PRU

Universal Mixing Rule with PR EoS.

import neqsim.thermo.system.SystemUMRPRU;

SystemUMRPRU lng = new SystemUMRPRU(110.0, 1.0);
lng.addComponent("methane", 0.92);
lng.addComponent("ethane", 0.05);
lng.addComponent("propane", 0.03);

Creating Custom Systems

Temperature and Pressure

// Create at specific T, P
SystemSrkEos fluid = new SystemSrkEos(300.0, 10.0);  // K, bar

// Change conditions later
fluid.setTemperature(350.0);
fluid.setPressure(50.0);

// With units
fluid.setTemperature(25.0, "C");
fluid.setPressure(50.0, "bara");

Components

// By name and moles
fluid.addComponent("methane", 100.0);

// By index
fluid.addComponent(0, 100.0);

// TBP fraction (for plus fractions)
fluid.addTBPfraction("C7+", 10.0, 150.0, 0.78);  // name, moles, MW, SG

// Set mole fractions directly
double[] z = {0.85, 0.10, 0.05};
fluid.setMolarComposition(z);

Phase Specifications

// Force number of phases
fluid.setNumberOfPhases(2);

// Specify phase types
fluid.setPhaseType(0, "gas");
fluid.setPhaseType(1, "oil");

// Allow solid phases
fluid.setSolidPhaseCheck(true);

System Methods

Initialization

// Initialize thermodynamic properties
fluid.init(0);  // Molar volumes only
fluid.init(1);  // Plus fugacity coefficients
fluid.init(2);  // Plus all derivatives
fluid.init(3);  // Plus second derivatives

Property Access

// Bulk properties
double rho = fluid.getDensity("kg/m3");
double MW = fluid.getMolarMass("kg/mol");
double H = fluid.getEnthalpy("kJ/kg");
double S = fluid.getEntropy("kJ/kgK");
double Cp = fluid.getCp("J/molK");
double Cv = fluid.getCv("J/molK");
double Z = fluid.getZ();
double kappa = fluid.getKappa();  // Cp/Cv

// Transport properties
double visc = fluid.getViscosity("cP");
double k = fluid.getThermalConductivity("W/mK");

// Phase properties
double gasZ = fluid.getGasPhase().getZ();
double liqRho = fluid.getLiquidPhase().getDensity("kg/m3");

Cloning

// Deep copy
SystemInterface copy = fluid.clone();

// Modify copy without affecting original
copy.setTemperature(400.0);