Hello, everybody. I have a problem with, I suppose, easy question. just have limited time and need to get correct answer.

stainless tube L = 2000 mm. Inlet-> Methane 1100 C. 1,5 m3/h. outside air 20 C.

So I need to find out whether a heat exchanger is requited or not.

Everything is clear but I never clearly understood WALL CONDITIONS...what should I choose and why?  Heat transfer coefficient or wall temperature? I suppose heat tran coef. but what number? I've done a heat exchanger exmeriment before but they just put 5 W/m2*K without explanation why, where it should be taken from.

And when other parameters must me applied? like surface heat generation rate and wall temperature?

Thank you for explanation in advance and sorry for asking elementary questions.