Question

Which among the following is the formula for Knudsen number?

(a) ^λ⁄L

(b) ^λ⁄2L

(c) ^λ⁄3L

(d) ^λ⁄4L

I had been asked this question in an interview for internship.

The doubt is from Dimensionless Numbers topic in division Dimensional and Model Analysis of Fluid Mechanics

Answer 1

The correct answer is (a) ^λ⁄L

The explanation is: The formula for Knudsen number is ^λ⁄L.  Knudsen number in fluid mechanics deals with gas dynamics. It is defined as the ratio of the molecular mean free path length to the representative scale length.