### 8.5.2. Fluid Models

#### 8.5.2.1. Multiphase Reactions

Multiphase Reactions involving particle phases refer to a reaction between one or more components in a particle phase and one or more components in a continuous phase. For details, see Multiphase Reactions and Combustion.

#### 8.5.2.2. Buoyancy for Particles

Depending on the flow type, buoyancy (gravity) terms may need to be modeled. The density of the particle material is often much higher than that of the carrier fluid, resulting in a buoyancy force. However, other forces may dominate over the buoyancy force such that its effect is not important. The relative size of three forces must be considered:

- The drag force

- The inertial force

- The buoyancy force

Often the buoyancy force can be neglected if the drag and inertial forces dominate. In general, if settling of the particles is thought to be important, then the buoyancy term should be included.

If the buoyancy term is not important for the particle phase, you may still need to include it if convection due to density variations in the continuous phase is important. This is independent of particle transport modeling.

#### 8.5.2.3. Turbulence for Particles

The turbulence model used in a particle tracking simulation only applies to the continuous phases. Turbulence can affect the particles through the Particle Dispersion force, but the particles can have no effect on the turbulence of the continuous phase, other than indirectly by affecting the velocity field. For details, see Turbulent Dispersion Force.

#### 8.5.2.4. Heat Transfer for Particles

Heat transfer between the particles and the continuous phase can be modeled. The Fluid Models form must use the `Fluid Dependent` option to model Heat Transfer. The heat transfer options for each phase are set on a per-material basis. For details, see Heat Transfer.

#### 8.5.2.5. Radiation for Particles

Radiation can be included in a particle transport calculation, but there is no radiation calculation in the particles themselves. To turn on radiation for particles, set the Radiation option to `Fluid Dependent`, and then select a radiation model on the Fluid Specific Models tab for the continuous fluid. The radiation option for particles themselves is unavailable on the Fluid Specific Models form (because it cannot assume any value other than `None`).

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