## Docs

A Radiation boundary condition defines the thermal radiation on a face or face set of the domain. It is defined by the reference temperature (sink temperature) and the emissivity $$\epsilon$$. the radiation heat flux is then given, involving the calculated temperature $$T$$ at the boundary and the Stefan Boltzman constant $$\sigma$$, by:
$q = \epsilon \sigma (T^{4} - T_{sink}^{4})$