Question

In the following equation, what does y signifies?

(a) Dispersion

(b) Displacement

(c) Diffusion

(d) Distance

This question was addressed to me during a job interview.

Question is from Molecular Diffusion topic in portion Mass Transfer of Bioprocess Engineering

Answer 1

Correct choice is (d) Distance

The explanation: In single-phase systems, the rate of mass transfer due to molecular diffusion is given by Fick’s law of diffusion, which states that mass flux is proportional to the concentration gradient. JA is the mass flux of component A, NA is the rate of mass transfer of component A, a is the area across which mass transfer occurs, DAB is the binary diffusion coefficient or diffusivity of component A in a mixture of A and B, CA is the concentration of component A, and y is distance, \(\frac{dC_A}{dy}\) is the concentration gradient, or change in concentration of A with distance.