Question

The ratio of inertial forces to viscous forces is called as ________

(a) Nusselt number

(b) Schimdt number

(c) Sherwood number

(d) Reynolds number

The question was posed to me in an interview.

I'm obligated to ask this question of External Mass Transfer topic in chapter Heterogenous Reactions of Bioprocess Engineering

Answer 1

Correct choice is (d) Reynolds number

The best I can explain: The Reynolds number is the ratio of inertial forces to viscous forces and is a convenient parameter for predicting if a flow condition will be laminar or turbulent. It can be interpreted that when the viscous forces are dominant (slow flow, low Re) they are sufficient enough to keep all the fluid particles in line, and then the flow is laminar. Even very low Re indicates viscous creeping motion, where inertia effects are negligible. When the inertial forces dominate over the viscous forces (when the fluid is flowing faster and Re is larger) then the flow is turbulent.