How to solve this problem about radiation?

Mr. Lee M-S

Hi! everyone.

I'm studying about temperature & velocity in the cylidrical heater(ID:0.1m, Length:0.7m).

Inlet Velocity:0.5m/s Heater Temp : 1000K

But radiation condition makes me craze.. Heater tempeature is about 1000K, so radiation effect can't be neglect. So I have to choose the radiation model. But I don't have any idea how to choose that. From the guide, optical thickness can be good guide line to choose that. I know optical thickness is aL, but I don't know how to calculate a, absorption coefficient. I tested a lot of case varying absorption coefficient now . so I know absorption coefficient effect temperature result significantly.

And why static temperature and total temperature is different in my result. what is problem?

Please make me free from this dilema.