I tried to do a sample model that applied the temperture on the inner and outer surface of the pipe. and get the HFL as results.
1)Is the HFL = surface heat flux.
2) I tried to use that HFL as loading instead of the outer temperture, why do I have different temperture at the outter surface as the results? would't it should be the same if 1 above is true?
If you solve the heat transfer equation in 1D with different essential (temperature) and natural (flux) boundary conditions you will see why you do not get the same results.