### 10.8.1. Domain Considerations

Whenever a domain material does not emit, absorb or scatter radiation, the `Surface to Surface` transfer mode option should be chosen. This option reduces the computational time without any changes in the results.

The following set of rules applies when modeling radiation in solid domains and in simulations with more than one domain:

- For solid domains where thermal radiation is important, the Monte Carlo model is the only available option.

- For domain interfaces using the Conservative Interface Flux option, the radiation model must be the same on both sides of the interface. That is, for Fluid-Solid, Solid-Solid, or Porous-Solid domain interfaces, the Monte Carlo model is the only available option.

- For a simulation with multiple solid domains, the radiation model can be set independently for each solid domain, subject to the previous rule.

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