[n7310889]

Hi all,
One thing I need to be clarified for my self is the difference between the "Radiation model" in the fluent (say DO, DTRM S2S etc) with the available radiation option under the thermal conditions dialog box for a wall boundary condition. Lets I try to explain with example which I understand. Then I will request you to amend me it if wrong.

#Radiation model is OFF: Let liquid coolant is passing through a very hot bare tube. If I wanna calculate radiation loss from the tube outer surface to the environment, I don't require to activate Radiation model. Instead I should just provide the external emissivity of the tube surface and the temperature of the external environment.

#Radiation model is ON: Now lets consider the same hot tube is enclosed by an evacuated glass tube. If I wanna calculate heat loss from the tube surface through the glass tube to the environment and my model also include the glass tube, then I need to activate any of the radiation models (s2s for instance).
However, if my model does not include the glass tube, I don't need to activate any of the radiation models. Instead, I can set an operating condition which will satisfy the evacuated glass tube environment: (for instance, operating temperature approximately 50C (prospective glass tube temperature of my model), Operating pressure 0 pascal and operating density 0 kg/m3; since evacuated).

Am I right? If not please help me to be clear the concept. I'll be grateful to you.
Thanks
n7310889