28) What is the relation between the thickness of the thermal boundary layer and the depth of the hydrodynamic boundary layer?
The ratio of the two thicknesses is governed by the Prandtl number. If the Prandtl number (Pr) is 1, the two boundary layers (hydrodynamic and thermal) are the same thickness. If the Pr > 1, the thermal boundary layer is thinner than the velocity boundary layer.
