[Cloud]

Hi everyone
I simulated a case about heat exchanger.I didn't select on radiation model. But about the wall boundary,I selected on mixed and entered 0.3 for External Emissivity,7 for HTC,293 for Free stream temperature,293 for External Radiation Temperature. I simulated another case same as case1 except the wall boundary. I selected on convection and 7 for HTC,293 for Free stream temperatue. I found the temperature of the wall was different.
I want to know the meaning of external emissivity and if I enter a number for external emissivity,the radiation model will be calculated? If the answer is yes, which radiation model will be calculated,RO,P1,S2S or else?

Thanks a lot for your time!