Chemical Engineering - Heat Transfer - Discussion

Conduction: In the laminar sublayer, the velocity gradient is very steep due to the very slow movement of fluid close to the wall. Heat transfer in this thin layer is primarily governed by conduction because the fluid particles in this region are almost stationary relative to each other, and molecular conduction dominates.

Convection: In the bulk flow of the fluid, heat transfer is primarily by convection due to the movement of fluid particles. However, in the laminar sublayer, the fluid motion is minimal, so convection is less significant.