Final answer:
The Nusselt number is strongly dependent on the Reynolds number for external flow heat transfer, whether it is laminar or turbulent.
Step-by-step explanation:
The Nusselt number represents the ratio of convective to conductive heat transfer in a fluid flow. It is strongly dependent on the Reynolds number for external flow heat transfer.
a) In laminar flow, the Nusselt number increases with the Reynolds number due to the growth of the thermal boundary layer. As the Reynolds number increases, the flow becomes more turbulent, resulting in a thicker boundary layer and higher convective heat transfer.
b) In turbulent flow, the Nusselt number has a more complex relationship with the Reynolds number. Initially, the Nusselt number increases with the Reynolds number due to the increased mixing and convection. However, at very high Reynolds numbers, the Nusselt number reaches a plateau or even decreases due to the formation of a turbulent boundary layer that reduces the heat transfer efficiency.
c) The Nusselt number is not independent of flow type. It varies significantly for laminar and turbulent flows.
d) There is a strong dependence of the Nusselt number on the Reynolds number for external flow heat transfer.