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:

\[q = \epsilon \sigma (T^{4} - T_{sink}^{4})\]


  • The emissivity takes values between 0 and 1

  • Emissivity equal to 1 represents blackbody radiation

  • Emissivity equal to 0 leads to zero value radiation heatflux

  • The radiation is considered as diffuse and gray (No dependency on the rotational angle and the wavelength)