I am trying to model heat flow from warm water in pipes imbedded in a four inch concrete slab. When I define the boundary conditions for the top of the concrete slab, I can only chose a constant heat transfer coefficient. The heat transfer coefficient is really a function of the temperature difference between the surface temperature of the concrete (which is being solved for by FLUENT) and the free stream temperature (an input for the boundary condition). This is given by; h=1.13(delta T)^0.33. Can anyone tell me in detail how to implement a User Defined Function for the heat transfer coefficient.

write an execute_at_end function which updates the value of h. (Use face / cell macros to get the temperature ) execute _at_end is executed end of each iteration ( steady case) and at the end of each time step ( unsteady case) -Ajay