An alternative approach to evaluate the average Nusselt number for mixed boundary layer conditions in parallel flow over an isothermal flat plate

In this paper, we present an alternative approach to evaluate the average Nusselt number for mixed boundary layer conditions in parallel flow over an isothermal flat plate. This approach can be used regardless of the critical Reynolds number where the flow transitions from laminar flow to turbulent flow. This approach is simple and uses graphical visualisation of the physical situation. This should assist comprehension and retention. It utilises the average quantity for the laminar boundary layer and the average value for turbulent boundary layer to obtain the average quantities for mixed boundary layers without the need to perform the usual integration. It can easily be incorporated into part of undergraduate chemical, mechanical and petroleum engineering curricula. A worked example is included to show the utility of the approach.