The COMSOL® Product Suite

Compute Thermodynamic Properties with the Liquid & Gas Properties Module

Software for Modeling Properties for Gas Mixtures, Liquid Mixtures, and Gas–Liquid Mixtures

When setting up and running CFD, heat transfer, and acoustics simulations, modeling the material properties correctly is crucial. With the Liquid & Gas Properties Module, you can accurately and easily compute density, viscosity, thermal conductivity, heat capacity, and other properties as functions of composition, pressure, and temperature.

What You Can Model with the Liquid & Gas Properties Module

Properties for CFD Simulations

The density and viscosity of fluids may depend on composition, pressure, and/or temperature. Obtaining accurate values for these properties is relevant, and may affect the design of devices and processes. The Liquid & Gas Properties Module gives you the tools to compute density and viscosity for gas mixtures of arbitrary composition. In addition, the module contains property models for liquid solutions, for example for aqueous solutions and solutions with organic solvents. For two-phase flow systems, the module features models to compute the equilibrium composition of the vapor and liquid phases as a function of pressure and temperature.

Properties for Heat Transfer Simulations

The simulation of heat transfer in fluids requires properties such as thermal conductivity and heat capacity, in addition to density and viscosity. As an example, when designing climate control and ventilation systems, the properties of air depend on relative humidity, pressure, and temperature, and these dependencies may be important to the accuracy of such modeling and simulation studies. This is also valid for coolants, as well as gases and fluids used in processes throughout different industries. The Liquid & Gas Properties Module includes models for the computation of thermal conductivity and heat capacity as a function of pressure and temperature. These properties can be computed for gas mixtures and liquid mixtures of arbitrary composition, and used for accurate heat transfer models and simulations.

Properties for Acoustics Simulations

Pressure acoustic waves propagate in fluids, often water or air, and depend on pressure, temperature, bulk viscosity, heat capacity, and thermal conductivity. In air, the relative humidity affects these properties. The accuracy of these properties, and thereby the accuracy of the pressure acoustics simulation results, depends on the variables mentioned above, all of which can be calculated with the Liquid & Gas Properties Module.

Benchmark model for displacement ventilation" alt="A displacement ventilation benchmark model showing temperature in degrees Kelvin, visualized using a heat camera color table, and streamlines

Temperature field in a benchmark model for displacement ventilation. The density, viscosity, and heat transfer properties of air depend on temperature, pressure, and humidity. The Liquid & Gas Properties Module can generate accurate functions for these dependencies.

A heat pipe model showing the temperature in a heat camera color table and the flow field in a rainbow color table. Temperature and flow field in a heat pipe. The model defines the mass and heat transfer problem in combination with the evaporation and condensation of the working fluid.
An acoustic calibration coupler model simulated with a rainbow color table. When high-fidelity measurement microphones are calibrated, a pressure reciprocity calibration method is used. The properties of moist air depend on the ambient pressure, temperature, and relative humidity. This dependence has to be accounted for in order to obtain accurate results.

Features and Functionality in the Liquid & Gas Properties Module

Thermodynamic Properties

The Liquid & Gas Properties Module includes models and parameters for calculating the following properties:

  • Heat of reaction
  • Heat of formation
  • Heat capacity
  • Viscosity
  • Density
  • Thermal conductivity
  • Binary diffusivities
  • Activity and fugacity
These properties can be calculated for liquid mixtures and gas mixtures. In addition, it can perform equilibrium calculations for gas–liquid systems, so-called flash calculations; gas–liquid–liquid systems; and liquid–liquid systems.
A 1D plot of the chloroform-methanol phase envelope with the dew point shown as a blue line and bubble point as a green dotted line. Phase envelope of a nonideal chloroform/methanol mixture. First, a temperature–composition diagram is constructed, highlighting an azeotrope of the mixture. Then, an enthalpy–composition diagram is generated, and isotherms are plotted.

Thermodynamic Models and Property Models

To calculate the properties listed above, the Liquid & Gas Properties Module uses a number of different thermodynamic models. The variety of models available reflects the fact that no thermodynamic model is able to describe all gases and liquids. The choice of model depends on the type of mixture and the conditions.

The following thermodynamic models are available for liquids and gases:

  • Ideal gas
  • Peng–Robinson
  • Peng–Robinson (Twu)
  • Soave–Redlich–Kwong
  • Soave–Redlich–Kwong (Graboski–Daubert)

For liquid mixtures, the following thermodynamic models are also available:

  • Chao–Seader (Grayson–Streed)
  • Wilson
  • NRTL
  • Regular solution
  • Extended regular solution
  • Ideal solution

In addition to the thermodynamic models, you can specify the model for the properties individually.

The COMSOL Multiphysics UI with a heat pipe model in the Graphics window and the thermodynamic property settings shown with the gas viscosity options expanded. The Settings window for defining thermodynamic systems allows you to select the thermodynamic model as well as property models for each property calculated by the module.

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