Question

A liquid solid mixture with 10% solid and 90% liquid is input to a dryer, some of the liquid evaporated and the product contains 60% solid and 40% liquid, what is the ratio of an amount of water evaporated and amount of input?

(a) 2:1

(b) 3:2

(c) 5:4

(d) 6:5

The question was asked during a job interview.

Question is from Solving Material Balance Problems for Single Units in chapter A General Strategy for Solving Material Balance Problems and Solving Material Balance Problems for Single Units of Basic Chemical Engineering

Answer 1

Right choice is (d) 6:5

To explain: Let the amount of input be F and the amount of evaporated water be W. Solid balance: 0.1*F = 0*W + 0.6*(F – W), => F/W = 6/5.