### 27.1.4. Material Details View: Fixed Composition Mixture

This panel describes the Material details view when creating a fixed composition mixture. Fixed composition mixtures can consist of pure substances only and not other fixed composition mixtures. You can include any combination of materials in a fixed composition mixture. To combine materials from different material groups, however, you must first select the Material Groups that contain those materials. For example, to select `Air at 25 C` and `Water at 25 C`, you would first need to select the groups `Air Data` and `Water Data`.

For details, see Multicomponent Flow in the CFX-Solver Modeling Guide.

#### 27.1.4.1. 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.

6. Select a material, from the Child Materials list box.

7. Enter the fixed Mass Fraction of the material within the mixture.

   The sum of the mass fractions for all the materials in a mixture must be 1.

#### 27.1.4.2. Mixture Properties Tab

Mixture Properties can be used to explicitly set values when the Ideal Mixture model produces unsatisfactory results. When you create a fixed composition mixture, the mixture properties are determined by mass averaging the properties of the component materials. In some cases, the ideal mixture rule used by the CFX-Solver may not be representative of the mixture properties. You can customize the individual thermodynamic and transport properties by selecting the appropriate check boxes 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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