i am trying to solve a radiation problem with COMSOL "general heat transfer" with surface to surface radiation (dependent variables temperature T et radiosity J) where i d like to simulate a semitransparent body. since COMSOL assumes a opaque surface the reflectivity is 1 - emissivity, what is not true in this case. the problem in my modifications lies in the modification of rhe radiosity expression J0=J (defaulte value). independent what expression I give for J0 it does not change. every time sending the same radiosity value to the other surfaces as it would do for an opaque surface. So how can I change the radiosity expression in a right way J0 = emissivity*sigma*T^4+reflectivity*irradiation instead of J0=J=emissivity*sigma*T^4+(1 - emissivity)*irradiation.

Thanks in advance for your help!!!

hello. I am a student of mechanical engineering. my ms project is about thermal cracking furnace. I need the code or software to simulate furnace. if lts posible for you to send for me a solved problem about simulation of furnace whit FEMLAB I will be plesure.