Reply To: Unrealistic Heat Transfer Coefficient and Total Surface Heat Flux values

[Federico]

Hello, 

which HTC are you using in Fluent? If using, Surface Heat Transfer coefficient, this will be based off a reference temperature in your Reference Values. The default is 300 K. For most flows however, a constant reference temperature is not applicable.

There is also the Wall Function HTC, but this should only be used for average y+ between 30 and 60.

Finally, since your boundary mesh is fine, you may use the y+ based HTC and Ref. Temperatures. This method uses the temperature found at y+ ~ 300 (again, the 300 value is the default value, but you can change this in References Values). The theory is that when y+ = 300 away from the wall, the fluid temperature approaches the bulk fluid temperature. However, this method may not be applicable on closely spaced fins, where the mesh does not reach y+ away from the walls.

You can check this article which summarizes this: Defining heat transfer coefficient (HTC) - Ansys Knowledge