Karthik R

Hello Vidyadhar,

S2S model is primarily for optically thin media and considers radiation exchanges between just the surfaces. It does not account for any absorption or emission by the fluid or solid media. The boundaries participate in radiation through view factor calculations. S2S model is for media with 0 optical thickness. The optical thickness of your medium is an important parameter that is used to determine which radiation model you should apply. If you are working with optically thick media, then perhaps you should think about using a different radiation model (DO model may be more applicable in your case).

Regarding your question on the coupled wall -  your understanding seems to be correct.

Hope this helps.

Best Regards,