Question

For Air-Water system Lewis Number equals to

(a) Approx 1

(b) 0

(c) Infinity

(d) 0 to 1

This question was posed to me at a job interview.

My question comes from Material Balance Concepts-Counter Current topic in section Interphase Mass Transfer of Mass Transfer

Answer 1

The correct choice is (a) Approx 1

Easy explanation: For the air-water system the simultaneous heat and mass transfer takes place. Therefore the Schmidt number (Sc) and Prandtl number (Pr) become equal. Lewis number= (Sc/Pr) equals to 1.