The S2S radiation model makes it possible to simulate thermal radiation exchange between diffuse surfaces forming a closed set. The treatment is valid only for a single radiation wavelength. The medium that fills the space between the surfaces is non-participating, that is it neither absorbs, emits, or scatters radiation. Therefore, the amount of radiation received and emitted by each surface is uniquely defined by the surface's optical properties and the thermal boundary conditions imposed on it. The surface properties are quantified in terms of emissivity, reflectivity, transmissivity and radiation temperature which depend neither on radiation wavelength nor direction.
The corresponding node (Surface-to-Surface Radiation in the screenshot below) is activated as soon as an S2S simulation is selected.