Question

For the Prandtl (Pr) number greater than unity, the thermal boundary layer is-___(thinner than/thicker than/same as) the hydrodynamic boundary layer?

Answer 1

In case of water and oils Pr number is greater than 1. For liquid metals and air, Pr number is less than 1, hence thermal boundary layer thickness will be more than the hydrodynamic boundary layer thickness$.$

$\therefore$ The answer is thicker.