Internal Film Resistance
The Internal Film Resistance subnode is available from the context menu (right-click the Wall Heat Transfer parent node) or from the Physics toolbar’s Attributes menu. Use it to define the film resistance.
Even if you do not expect a boundary layer to build up, the thermal film theory works well for laminar flow profiles. In fact, there is an analytical solution available to the Nusselt number for laminar flow in circular tubes (Nu = 3.66).
Film Resistance
The default Internal film resistance model is Automatic and the Nusselt number is computed as described in the section Theory for the Heat Transfer in Pipes Interface. For User defined enter a value for the Nusselt number (dimensionless). The default is 3.66.