Thermal Conductivity Models

This guide documents the thermal conductivity calculation methods available in NeqSim for gas, liquid, and multiphase systems.

Overview
Available Models
Model Selection Guide
Usage Examples

Overview

Thermal conductivity ($\lambda$ or $k$) describes a material’s ability to conduct heat. It is essential for:

Heat exchanger design
Pipeline heat loss calculations
Thermal simulation of process equipment

Units:

Default output: W/(m·K) (Watts per meter-Kelvin)

Setting a conductivity model:

fluid.getPhase("gas").getPhysicalProperties().setConductivityModel("Chung");
fluid.getPhase("oil").getPhysicalProperties().setConductivityModel("PFCT");
fluid.getPhase("gas").initPhysicalProperties();
fluid.getPhase("oil").initPhysicalProperties();

Select the model after the flash and initial property calculation, then reinitialize each changed phase as shown. Model keys are case-sensitive. Unsupported keys currently fall back to PFCT, so use one of the documented keys and cover model selection in tests.

Available Models

PFCT (Pedersen)

The Pedersen Corresponding States method uses methane as a reference fluid with molecular weight corrections.

Class: PFCTConductivityMethodMod86

Principle: Uses corresponding states with methane as reference:

\[\lambda_{mix} = \lambda_{ref}(T_0, P_0) \cdot \frac{\alpha_{mix}}{\alpha_0}\]

where:

$\lambda_{ref}$ is methane thermal conductivity at corresponding conditions
$T_0, P_0$ are the corresponding temperature and pressure
$\alpha$ are molecular weight correction factors

Corresponding state mapping: $T_0 = T \cdot \frac{T_{c,ref}}{T_{c,mix}} \cdot \frac{\alpha_0}{\alpha_{mix}}$

\[P_0 = P \cdot \frac{P_{c,ref}}{P_{c,mix}} \cdot \frac{\alpha_0}{\alpha_{mix}}\]

Applicable phases: Gas, Oil

Best for:

Petroleum mixtures
Wide pressure-temperature ranges
Systems with characterized fractions

Usage:

fluid.getPhase("oil").getPhysicalProperties().setConductivityModel("PFCT");

Chung Method

The Chung method (1988) is a corresponding states correlation based on kinetic theory.

Class: ChungConductivityMethod

Equation (dilute gas): $\lambda_0 = \frac{7.452 \eta_0 \Psi}{M}$

where:

$\eta_0$ is the dilute gas viscosity
$\Psi$ is a correction factor
$M$ is molar mass

The correction factor accounts for:

Polyatomic structure
Polar effects
Association

Dense fluid correction: $\lambda = \lambda_0 \cdot G_2(T^*, \rho^*) + B_1 q B_2$

where $G_2$ and $B$ terms account for density effects.

Applicable phases: Primarily gas phase

Best for:

Gas-phase calculations
Polar gases
As baseline correlation

Usage:

fluid.getPhase("gas").getPhysicalProperties().setConductivityModel("Chung");
fluid.getPhase("gas").initPhysicalProperties();

Chung Dense Method

Chung-dense implements the full Chung et al. correlation, including dilute-gas and density-dependent contributions. Use it when pressure or liquid-like density makes the dilute Chung model insufficient.

Class: ChungDenseConductivityMethod

Applicable phases: Gas and liquid

Usage:

fluid.getPhase("gas").getPhysicalProperties().setConductivityModel("Chung-dense");
fluid.getPhase("gas").initPhysicalProperties();

Polynomial Correlation

Uses component-specific polynomial coefficients from the database.

Class: Conductivity (in liquid package)

Equation: $\lambda = A + BT + CT^2$

where A, B, C are component-specific parameters.

Database columns: LIQUIDCONDUCTIVITY1, LIQUIDCONDUCTIVITY2, LIQUIDCONDUCTIVITY3

Mixing rule: $\lambda_{mix} = \sum_i x_i \lambda_i$

Applicable phases: Liquid

Best for:

Pure components with available parameters
Simple liquid mixtures

Usage:

fluid.getPhase("oil").getPhysicalProperties().setConductivityModel("polynom");
fluid.getPhase("oil").initPhysicalProperties();

CO2 Reference

Pure-CO₂ thermal conductivity model implemented as a polynomial fit to reference data generated with CoolProp. The implementation is checked against NIST values in CO2ConductivityMethodTest and uses Span-Wagner properties if a usable density is unavailable.

Class: CO2ConductivityMethod

Constraint: The phase must contain pure CO₂. The implementation rejects mixtures; do not use CO2Model for CO₂-rich multicomponent streams. NeqSim does not enforce a temperature-pressure validity envelope for this polynomial, so validate extrapolated states independently.

Best for:

Pure CO₂ systems
CCS applications
Reference calculations

Usage:

fluid.getPhase("gas").getPhysicalProperties().setConductivityModel("CO2Model");
fluid.getPhase("gas").initPhysicalProperties();

Model Selection Guide

Application	Recommended Model	Notes
Petroleum mixtures	PFCT	Corresponding states with MW correction
Low-density gas	Chung	Dilute-gas contribution
Dense gas or liquid	Chung-dense	Includes density-dependent contribution
Simple liquid mixtures	polynom	Uses database parameters
Pure CO₂	CO2Model	Rejects mixtures; validate extrapolation
Wide P-T range	PFCT	Robust extrapolation
Polar systems	Chung	Includes polar corrections

Additional implemented keys are friction theory, Filippov, WaterModel, and H2Model. They are specialized models and should be selected only with a composition and phase appropriate to the underlying correlation.

Usage Examples

Basic Conductivity Calculation

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

// Create and flash fluid
SystemInterface fluid = new SystemSrkEos(350.0, 50.0);
fluid.addComponent("methane", 0.85);
fluid.addComponent("ethane", 0.10);
fluid.addComponent("propane", 0.05);
fluid.setMixingRule("classic");

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

// Initialize physical properties
fluid.initPhysicalProperties();

// Get thermal conductivity
double gasConductivity = fluid.getPhase("gas").getThermalConductivity("W/mK");
if (!(gasConductivity > 0.0)) {
    throw new IllegalStateException("Expected positive gas thermal conductivity");
}

Comparing Conductivity Models

String[] models = {"PFCT", "Chung-dense"};
double[] conductivities = new double[models.length];

for (int i = 0; i < models.length; i++) {
    SystemInterface fluid = new SystemSrkEos(350.0, 50.0);
    fluid.addComponent("methane", 0.85);
    fluid.addComponent("ethane", 0.10);
    fluid.addComponent("propane", 0.05);
    fluid.setMixingRule("classic");
    ThermodynamicOperations ops = new ThermodynamicOperations(fluid);
    ops.TPflash();
    fluid.initProperties();
    
    fluid.getPhase("gas").getPhysicalProperties().setConductivityModel(models[i]);
    fluid.getPhase("gas").initPhysicalProperties();
    conductivities[i] = fluid.getPhase("gas").getThermalConductivity("W/mK");
}

Conductivity vs Pressure

SystemInterface baseFluid = new SystemSrkEos(350.0, 10.0);
baseFluid.addComponent("methane", 1.0);
baseFluid.setMixingRule("classic");

double[] pressuresBara = {10, 50, 100, 150, 200};
double[] conductivities = new double[pressuresBara.length];

for (int i = 0; i < pressuresBara.length; i++) {
    SystemInterface fluid = baseFluid.clone();
    fluid.setPressure(pressuresBara[i], "bara");
    
    ThermodynamicOperations ops = new ThermodynamicOperations(fluid);
    ops.TPflash();
    fluid.initPhysicalProperties();
    
    conductivities[i] = fluid.getPhase(0).getThermalConductivity("W/mK");
}

Two-Phase System

SystemInterface fluid = new SystemSrkEos(280.0, 30.0);
fluid.addComponent("methane", 0.5);
fluid.addComponent("n-pentane", 0.5);
fluid.setMixingRule("classic");
fluid.setMultiPhaseCheck(true);

ThermodynamicOperations ops = new ThermodynamicOperations(fluid);
ops.TPflash();
fluid.initPhysicalProperties();

double gasConductivity = fluid.hasPhaseType("gas")
    ? fluid.getPhase("gas").getThermalConductivity("W/mK") : Double.NaN;
double oilConductivity = fluid.hasPhaseType("oil")
    ? fluid.getPhase("oil").getThermalConductivity("W/mK") : Double.NaN;

Physical Background

Kinetic Theory (Dilute Gas)

For dilute gases, thermal conductivity is related to viscosity through:

\[\lambda = \frac{f \cdot \eta \cdot C_v}{M}\]

where:

$f$ is the Eucken factor (typically 1.32 for monoatomic, 1.77 for polyatomic)
$\eta$ is dynamic viscosity
$C_v$ is heat capacity at constant volume
$M$ is molar mass

Mixing Rules

For mixtures, thermal conductivity is typically calculated using:

Mass fraction weighting: $\lambda_{mix} = \sum_i w_i \lambda_i$

Molar weighting with interaction: $\lambda_{mix} = \sum_i \sum_j \frac{x_i x_j \lambda_{ij}}{\sum_k x_k \phi_{ik}}$

where $\lambda_{ij}$ is a combining rule and $\phi_{ik}$ is an interaction factor.

Pressure Effects

Thermal conductivity increases with pressure, particularly in dense fluids:

At low pressures: $\lambda \approx \lambda_0(T)$
At high pressures: $\lambda = \lambda_0 + \Delta\lambda(\rho)$

The PFCT method accounts for this through corresponding states mapping to reference fluid behavior.

Temperature and Pressure Dependence

Gases

Conductivity increases with temperature (~$T^{0.8}$)
Weak pressure dependence at low-moderate pressures
Significant increase at high pressures (dense gas)

Liquids

Conductivity typically decreases with temperature
Slight increase with pressure
Water is an exception (increases with T up to ~130°C)

References

Pedersen, K.S., et al. (1989). Thermal Conductivity of Crude Oils. Chem. Eng. Sci.
Chung, T.H., et al. (1988). Generalized Multiparameter Correlation. I&EC Res.
Huber, M.L., et al. (2016). New International Formulation for the Thermal Conductivity of CO₂. J. Phys. Chem. Ref. Data.
Scalabrin, G., et al. (2006). A Reference Multiparameter Thermal Conductivity Equation for Carbon Dioxide. J. Phys. Chem. Ref. Data.
Poling, B.E., et al. (2001). The Properties of Gases and Liquids, 5th Ed.

Table of Contents

Overview

Available Models

PFCT (Pedersen)

Chung Method

Chung Dense Method

Polynomial Correlation

CO2 Reference

Model Selection Guide

Usage Examples

Basic Conductivity Calculation

Comparing Conductivity Models

Conductivity vs Pressure

Two-Phase System

Physical Background

Kinetic Theory (Dilute Gas)

Mixing Rules

Pressure Effects

Temperature and Pressure Dependence

Gases

Liquids

References