### 27.1.5. Material Details View: Variable Composition Mixture

This panel describes the Material details view when creating a variable composition mixture. Components of a variable composition mixture can be pure substances and fixed composition mixtures. For details, see Multicomponent Flow in the CFX-Solver Modeling Guide.

#### 27.1.5.1. Basic Settings Tab

1. Select the Material Group(s) that contain the required materials.

2. Use Materials List to add new materials to the mixture.

3. The Material Description field is optional.

   For details, see Material Description.

4. Select the Thermodynamic State.

   For details, see Thermodynamic State.

5. Optionally set a custom coordinate frame for any material properties that depend on expressions in X, Y or Z.

   For details, see Coordinate Frame, Coordinate Frames, and Coordinate Frames in the CFX-Solver Modeling Guide.

#### 27.1.5.2. Mixture Properties Tab

In some cases, the ideal mixture rule used by the CFX-Solver may not be representative of the mixture properties.

When you create a variable composition mixture (and also when you create a reacting mixture), the thermodynamic mixture properties can be determined by:

- Mass averaging the properties of the component materials (by choosing the corresponding `Ideal Mixture` option), or

- Applying custom functions based on the properties and mass fractions of the component materials (by choosing options other than `Ideal Mixture`).

The Thermodynamic Properties settings include:

- Equation of State, with these options:

  - `Ideal Mixture` - This option uses mass averaging of the properties of the component materials.

  - `Mixture Density` - You specify values and/or CEL expressions for:

    - Density

    - The partial derivative of density with respect to pressure (at constant temperature), and

    - The partial derivative of density with respect to temperature (at constant pressure).

    These quantities can be functions of component mass fractions and component properties (such as density).

  - `Mixture Pressure` - You specify values and/or CEL expressions for:

    - Absolute pressure

    - The partial derivative of absolute pressure with respect to specific volume (at constant temperature), and

    - The partial derivative of absolute pressure with respect to temperature (at constant specific volume).

    These quantities can be functions of component mass fractions and component properties.

- Specific Heat Capacity, with these options:

  - `Ideal Mixture`

  - `Mixture Specific Heat Capacity` - You specify the type of heat capacity (as being based on constant volume or constant pressure). You also specify values and/or CEL expressions for:

    - Specific heat capacity

    - Specific enthalpy

    - Specific entropy

    These quantities can be functions of component mass fractions and component properties (such as specific heat capacity, static enthalpy, and static entropy, respectively).

  When entering expressions for the Thermodynamic Properties settings, terms that involve component properties should adhere to the general variable syntax described in Quantitative CEL Functions in ANSYS CFX.

You can override the individual transport properties by selecting the appropriate options and directly specifying the mixture properties.

For details, see Mixture Properties (Fixed, Variable, Reacting) in the CFX-Solver Modeling Guide.

For additional information on options for specific heat capacity, see Specific Heat Capacity in the CFX-Solver Modeling Guide.

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