Ok, discovered one more thing today - don't use the heat flux option unless you know the value of heat flux - it treats the wall as adiabatic otherwise (if you leave it zero) :p

Hello to everyone in this conversation, I am simulating like one of this model for both parallel and counter flow. I have gained some facts about this simulation. Thanks a lot. But problem is I have two shadow wall created as default how Can create my boundary condition for 2nd wall and shadow since there is 2 interfaces created.