Outlet boundary condition

Asghari

Hello,every body. please,take into consideration,two bottom example that must be solved by cfd: 1-The flow entered into cylinderical and axisymmetric tube. Wall temperature in upstream is 350 kelvin and wall temperature in downstream is 300 kelvin. 2-There is two cylinderical and concentric tube ; first fluid entered from inner cylinderical duct in 300 kelvin and second fluid entered from space between inner and outer cylinder and in opposed direction(countercurrent)with first fluid and in 350 kelvin . Please,for two given example,answer to this common question: a)It is clear that outlet boundary condition in first example , is not fully developed condition(because of temperature is changing from inlet to outlet),therefor , please, describe that how to define outlet boundary condition? b)In second example, what is outlet boundary conditions for both flow?(fully developed condition could not used due to temperature variations from upstream to downstream for both fluid.)