### 10.7.1. Fluid Models

Information on radiation modeling in solid/multiple domains is available in Domain Considerations.

#### 10.7.1.1. Number of Histories

Optional parameter to indicate the total number of histories to be tracked for the simulation. The default value is 10000. This can have a large effect on the accuracy of simulation results. For details, see Monte Carlo Statistics. For information on interpreting Monte Carlo results, see Monte Carlo Model.

#### 10.7.1.2. Transfer Mode

The Transfer Mode setting defines which radiative transfer mode is enabled. The default value is `Participating Media` (that is, the domain material emits, absorbs, and/or scatters radiation). The `Surface to Surface` option implies that volumetric emission, absorption and scattering are ignored regardless of the specified material properties.

Note: Solution time may be adversely affected when using the `Surface to Surface` option in a case involving a subdomain that only partially covers the whole domain. With the `Surface to Surface` option, the CFX-Solver tries to reduce the radiation mesh to a single element (because only surfaces are of interest) but the presence of the subdomain causes the number of elements to be at least two, triggering a potentially time-consuming ray trace. This problem applies to both the Discrete Transfer and Monte Carlo models.

The workaround is to use the `Participating Media` option instead of the `Surface to Surface` option and adjust the coarsening controls to produce a coarser radiation mesh than the default. Choosing a coarsening rate that produces a few hundred radiation elements should result in a solution similar to that under the `Surface to Surface` option, but with perhaps not the same resolution of the intensity field at the boundaries.

#### 10.7.1.3. Spectral Model

See Spectral Model.

#### 10.7.1.4. Scattering Model

See Scattering Model.

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