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[FAQ]

The “Surface Heat Transfer Coefficient” is calculated with “wall temperature”, “total surface heat flux” and a “reference temperature”. This reference temperature is a global value used on all faces. The accuracy of the surface htc (heat transfer coefficient) depends on the accuracy of the simulation and this reference or bulk temperature. For complex geometries it can be next to impossible to set a good reference temperature for large surfaces. Nevertheless, this is the parameter that is used by most Nusselt number correlations. The “Wall Func. Heat Tran. Coef.” depends on the local solution of the flow field in a cell next to a wall. It is completely independent of the surface heat flux. Therefore it exists also for adiabatic walls. Since wall function htc depends on the turbulence model and the local temperature in the cell and at the wall the value has a strong dependency on the mesh resolution. It is quite rare that this parameter is used to judge the results of a simulation. For a mesh with large y+ values and a reasonable reference temperature both parameters have similar results. A study of the differences with some additional explanations is available in solution 2043378.