### 12.4.4. Fluid Specific Models Tab

The Fluid Specific Models tab contains settings for fluid-specific properties. It appears for multiphase simulations and when particles are included in the domain.

Which options are available depends on the simulation set up, including the type and number of fluids used in the simulation (for example, single or multicomponent, single or multiphase, reacting or non-reacting), and whether Additional Variables have been created.

#### 12.4.4.1. Fluid List Box

This list box is used to select a fluid (which can, in some cases, represent a solid). The rest of the tab contains settings for the selected fluid.

#### 12.4.4.2. Kinetic Theory

The Kinetic Theory settings control the solid particle collision model. When you set Kinetic Theory to `Kinetic Theory`, you should set the granular temperature model and radial distribution function. CFX-Pre will also set the Solid Pressure Model, Solid Bulk Viscosity, and the Solid Shear Viscosity settings to `Kinetic Theory`.

For details on these settings: | See:
--- | ---
Granular temperature model | Granular Temperature
Radial distribution function | Kinetic Theory Models for Solids Pressure
Solid pressure model | Solids Pressure
Solid bulk viscosity | Solids Bulk Viscosity
Solid shear viscosity | Solids Shear Viscosity

For modeling information about solid particle collision models, see Solid Particle Collision Models in the CFX-Solver Modeling Guide.

For theoretical information about solid particle collision models, see Solid Particle Collision Models in the CFX-Solver Theory Guide.

#### 12.4.4.3. Heat Transfer Model

If you have set Heat Transfer to `Fluid Dependent` on the Fluid Models tab, Heat Transfer Model options appear on the fluid-specific tabs for each Eulerian phase. If the heat transfer occurs between two fluids, then additional information must be entered on the Fluid Pairs tab. Information on heat transfer between phases is available in Interphase Heat Transfer in the CFX-Solver Modeling Guide.

Some of the available Heat Transfer Model options are similar to those in the single-phase case. See Heat Transfer for details on the following options:

- `None`

- `Isothermal`

- `Thermal Energy`

- `Total Energy`

Additional Heat Transfer Model options include:

- `Particle Temperature`: Can only be used for particle transport fluids and solids. For details, see Heat Transfer in the CFX-Solver Modeling Guide.

- `Saturation Temperature`: Can only be used for a fluid that is a component of a homogeneous binary mixture. This model is applicable only when the heat transfer modeling is inhomogeneous. For its most common use, one of the phases of a two-phase flow is set to use `Saturation Temperature` while the other uses a different Heat Transfer Model option, such as `Thermal Energy` or `Total Energy`. The `Saturation Temperature` option behaves similarly to the `Isothermal` option except that, instead of the fluid temperature being forced to be the specified Fluid Temperature value, the fluid temperature is forced to be the saturation temperature as computed from the saturation properties of the homogeneous binary mixture.

- `Small Droplet Temperature`: Can only be used for a fluid that has Morphology > Option set to `Droplets with Phase Change`. For details, see Droplet Condensation Model in the CFX-Solver Modeling Guide.

#### 12.4.4.4. Turbulence Model

If you have set Turbulence to `Fluid Dependent` on the Fluid Models tab, the Turbulence Model option appears on the fluid-specific tabs for each Eulerian phase. The models available are similar to those available in single-phase simulations, with the following exceptions:

- For dispersed fluid, or dispersed/polydispersed solid phases, only the `Dispersed Phase Zero Equation`, `Laminar` or `Zero Equation` models are available. The Dispersed Phase Zero Equation model is the recommended choice. For details, see Phase-Dependent Turbulence Models in the CFX-Solver Modeling Guide.

- The `LES` and `DES` models are available for transient simulations for the continuous phase.

For details, see Turbulence.

#### 12.4.4.5. Turbulent Wall Functions

The turbulent wall functions are selected automatically, but apply only to the current fluid. For details, see Wall Function.

#### 12.4.4.6. Combustion Model

If you have set the reaction or combustion model to Fluid Dependent on the Fluid Models tab, the Reaction or Combustion Model option can appear on the Fluid Specific Models tab for each Eulerian phase. You will only be able to pick a combustion model for fluids that are reacting mixtures. The models available are similar to those available in single-phase simulations. For details, see:

- Phasic Combustion in the CFX-Solver Modeling Guide

- Reaction or Combustion Model.

#### 12.4.4.7. Erosion Model

The erosion properties specified on this form are applied to all wall boundaries. The wall boundaries can also have erosion properties set to override the global settings specified here. For details, see Erosion in the CFX-Solver Modeling Guide.

#### 12.4.4.8. Fluid Buoyancy Model

This option is available for multiphase buoyant flows and/or buoyant flows that include particles (set on the Basic Settings tab). For details, see Buoyancy in Multiphase Flow in the CFX-Solver Modeling Guide.

#### 12.4.4.9. Solid Pressure Model

This is available for `Dispersed Solid` Eulerian phases (phases with `Dispersed Solid` as the Morphology setting). For details, see Solid Pressure Force Model in the CFX-Solver Modeling Guide.

#### 12.4.4.10. Component Details

This is available for each Eulerian phase in the simulation that is a mixture of more than one component. It does not apply to fluids or solids using the particle tracking model. The options available are the same as those on the Fluid Models tab in a single-phase simulation. For details, see Component Details.

If the component transfer occurs between two fluids, then additional information must be entered on the Fluid Pairs tab. This is only possible when more than one multicomponent fluid exists in a simulation. For details, see Interphase Species Mass Transfer in the CFX-Solver Modeling Guide.

#### 12.4.4.11. Additional Variable Models

This is available for each Eulerian phase in the simulation when Additional Variables have been created as well as selected and set to `Fluid Dependent` on the Fluid Models tab. The options available are the same as those on the Fluid Models tab in a single-phase simulation. It does not apply to fluids or solids using the particle tracking model. For details, see Additional Variable Details.

If the Additional Variable transfer occurs between two fluids, then additional information must be entered on the Fluid Pairs tab. This is possible only when more than one phase in a simulation includes Additional Variables. For details, see Additional Variables in Multiphase Flow in the CFX-Solver Modeling Guide.

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