# Mass Transfer Questions and Answers – Cost Variance with Reflux Ratio

This set of Mass Transfer Questions for campus interviews focuses on “Cost Variance with Reflux Ratio”.

1. Most economical cost is
a) Minimum cost
b) Optimum cost
c) Balanced cost
d) Fixed cost

Explanation: Optimum cost will be efficient at any conditions.

2. Consider an operating line touches the equilibrium line, and then the fixed cost becomes
a) Minimum
b) Infinite
c) No fixed cost
d) None of the mentioned

Explanation: If the operating line touches the equilibrium line, obviously the number of trays becomes infinite leads to infinite fixed cost.

3. If the operating cost is low, then the fixed cost is more.
a) True
b) False

Explanation: The operating cost will be low if the numbers of trays are more; simultaneously if the number of trays increases.

4. If the reflux ratio increases _________ increases.
a) Fixed cost
b) Operating cost
c) Optimum
d) All of the mentioned

Explanation: If the reflux ratio increases, the load of condenser has to increase which leads to increase of operating cost.

5. If the reflux increases ________ increases in the fractionator.
a) Diameter
b) Length
c) Volume
d) None of the mentioned

Explanation: If the reflux ratio is more, reflux increases. For the more condensed liquid, the column diameter should be more.
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6. Total cost is
a) Operating + optimum cost
b) Fixed + optimum cost
c) Fixed + operating cost
d) None of the mentioned

Explanation: The total cost is estimated by the sum of cost of trays and other devices like condenser, reboiler which equals the sum of operating and fixed cost.

7. At optimum reflux ratio,
a) Operating and optimum cost are equal
b) Operating and fixed cost are equal
c) Fixed and optimum cost are equal
d) Total and optimum cost are equal

Explanation: To get the optimum cost the cost used for the trays and other devices should be the same.

8. Total cost will be minimum at
a) Minimum reflux ratio
b) Maximum reflux ratio
c) Optimum reflux ratio
d) None of the mentioned

Explanation: At optimum reflux ratio, the fixed cost and the operating cost will be equal so the total cost will be minimum.

9. A designer gave us a report on distillation column and said he was perfect.

a) True
b) False

Explanation: We can get the minimum operational cost only at minimum reflux ratio.

10. Estimate the fixed cost if the operational cost is 7 lakhs and the total cost is 15 lakhs.
a) 21 lakhs
b) 8 lakhs
c) 7 lakhs
d) None of the mentioned

Explanation: Total cost= fixed cost + operational cost.

11. Estimate the operational cost if the fixed cost is 15 lakhs.
(Hint: reflux ratio= optimum)
a) 15 lakhs
b) 30 lakhs
c) 0
d) None of the mentioned

Explanation: At optimum reflux ratio, the fixed cost = operational cost= 15 lakhs.

Sanfoundry Global Education & Learning Series – Mass Transfer.

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