Question

The Prandtl Number approximates ___________

(a) Momentum diffusivity to thermal diffusivity

(b) Thermal diffusivity to momentum diffusivity

(c) Shear stress to thermal diffusivity

(d) Thermal diffusivity to kinematic viscosity

I have been asked this question in an international level competition.

Origin of the question is Universal Velocity Distribution topic in section Viscous Flow & Turbulent Flow of Fluid Mechanics

Answer 1

Correct answer is (a) Momentum diffusivity to thermal diffusivity

Easiest explanation: The Prandtl number is a dimensionless number. It approximates the ratio of momentum diffusivity to thermal diffusivity. It can be expressed as Pr = v/ α(1).  Where α= thermal diffusivity and v = momentum diffusivity.