### 6.2.2. Gas Properties Tab

Figure 6.2: Gas Properties Tab

This tab contains the required gas property input data.

Frame 1: Gas Properties Model

This frame gives the following options:

- Ideal gas

- Real gas

  For the `Real gas` option, material properties are derived from the Aungier-Redlich-Kwong equation, which is mentioned in Overview and Limitations in the Fluent User's Guide.

You may also select whether to choose a standard material from the gas properties database, or choose to specify the detailed material properties as shown in Figure 6.2: Gas Properties Tab.

The list of available gases can be seen in the drop-down menu in Vista CCD. At the time of writing, this list was:

- air

- carbon-dioxide

- hydrogen

- methane

- nitrogen

- oxygen

- parahydrogen

- propylene

- R123

- R125

- R134a

- R141b

- R142b

- R245fa

- water (steam)

Frame 2: User Specified Properties

This frame is enabled should you choose to specify the material properties. Only fields relevant to the selected gas model are enabled. This frame contains the Cp polynomial coefficients frame, and other frames. For the Ideal Gas model, only the Gas constant, Gamma and Kinematic viscosity are required. For the real gas model Gamma is no longer required; but the Critical pressure, Critical temperature, Critical specific volume and Acentric factor along with the Cp polynomial definitions as a function of temperature need to be specified.

You can specify viscosity as follows:

- `Sutherland (air)`

  Viscosity is calculated as a function of temperature, using Sutherland's law.

- `Dynamic`

  The dynamic viscosity that you specify is treated as a constant.

- `Kinematic`

  The kinematic viscosity that you specify is treated as a constant.

  In real world cases, kinematic viscosity may change significantly with pressure (via density changes). Consequently it may be advisable to use the dynamic viscosity instead, because it varies less with pressure.

Release 18.2 - © ANSYS, Inc. All rights reserved.