with Ai the surface area (SI unit: m²) and
εi the surface emissivity (dimensionless). See
Theory for Surface-to-Surface Radiation for more details.
This allows a network representation of the radiative heat rate with Ebi and
Ji as nodes. The surface resistance tends towards 0 for a large surface or a surface with large emissivity, for which the blackbody approximation holds.
When considering the surface of index i as part of an enclosure, the net radiative heat rate is expressed as:
where Fij is the view factor for surfaces
i and
j.
These expressions are predefined options in the Radiative Thermal Resistor feature. Further simplifications can be made on the net radiation exchange when the blackbody assumption holds
(ε1=
ε2=1).