obtain wall heat flux
 

hi all

i have a problem with fluent. the problem looks simple but i don't know why i cant do it well. i have a tube that i know what is the inlet and outlet temp and the aim is obtain the wall heat flux. we want to see how the evaporation of water surround this tube take place (imagine a tube of heat exchanger). i use velocity inlet and pressure outlet boundary condition.

thanks in advance for your kindly helps