Question

Prandtl number is the ratio of

• A. Mass diffusivity to thermal diffusivity
• B. Thermal diffusivity to mass diffusivity
• C. Thermal diffusivity to momentum diffusivity
• D. Momentum diffusivity to thermal diffusivity

Hint:

Prandtl number is \(Pr=\frac{\nu}{\alpha}\), that is, momentum diffusivity divided by thermal diffusivity.

Answer 1

The Correct Option is D

Prandtl number is a dimensionless number used in heat transfer. It is represented by: \[ Pr \] It is defined as: \[ Pr=\frac{\nu}{\alpha} \] where, \[ \nu=\text{momentum diffusivity} \] and \[ \alpha=\text{thermal diffusivity} \] Momentum diffusivity tells how fast momentum spreads in a fluid. Thermal diffusivity tells how fast heat spreads in a fluid. Therefore, Prandtl number compares momentum diffusion with heat diffusion. So: \[ Pr=\frac{\text{momentum diffusivity}}{\text{thermal diffusivity}} \] Hence, the correct answer is: \[ \text{Momentum diffusivity to thermal diffusivity} \]