# Mass Transfer Questions and Answers – Drying-Rate of Batch Drying

This set of Mass Transfer Multiple Choice Questions & Answers (MCQs) focuses on “Drying-Rate of Batch Drying”.

1. Direct dryers are ___________
a) Batch driers
b) Continuous driers
c) Semi-batch driers
d) None of the mentioned

Explanation: In batch drying process the heat is directly allowed over the solids.

2. Cabinet/ Tray driers are direct driers.
a) True
b) False

Explanation: In cabinet the solids are loaded and the hot gas is passed over. So it’s a kind of direct drying operation.

3. For estimating the drier size it is necessary to know _________
a) Time of drying
b) Heat of drying
c) Speed of drying
d) All of the mentioned

Explanation: The design of drier is based on drying curve rate which demonstrates the time rate.

4. For a batch drying, the wet surface should be more compare to dry surface.
a) True
b) False

Explanation: For an effective batch drying operation to take place, the ratio of wet and dry surface should be same.

5. Constant drying conditions include
a) Temperature constant
b) Humidity constant
c) Velocity constant
d) All of the mentioned

Explanation: The temperature, humidity and velocity should be constant for constant drying condition.
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6. Find the missing position.

a) Time
b) Speed
c) Water vapour
d) None of the mentioned

Explanation: The moisture content decreases with time.

7. Calculate the flux (kg/sq.m sec) if
Mass of dry solid = 8 kg; Wet surface area = 4 sq.m; Change in moisture content with time is 0.4 /sec;
a) 0.4
b) 0.6
c) 0.8
d) 0.9

Explanation: Flux = 8/4 * 0.4 = 0.8.

8. The other part than the constant rate period in the Batch- Drying curve is falling rate period.
a) True
b) False

Explanation: After the constant rate period, the unsaturated drying surface is known as falling rate period.

9. Find the gas phase mass transfer co-efficient for a unbound moisture to remove if the flux is 5 kg/sq.m sec and the difference in humidity of the liquid and the main stream is 0.5 units.
a) 5
b) 10
c) 20
d) 30

Explanation: Flux= Mass transfer co-efficient * (Ys-Y)
Mass transfer co-efficient= 5/0.5 = 10.

10. The value of _________ remains constant while drying if speed and direction of gas flow never change.
a) Mass transfer co-efficient
b) Humidity
c) Moisture
d) None of the mentioned

Explanation: If the speed and the direction of gas never change the rate remains same so the mass transfer co-efficient remain same.

11. If the dry spot appears in the substance in the batch drying curve at ___________
a) Critical moisture content
b) Equilibrium moisture content
c) Bound moisture
d) Unbound moisture

Explanation: After the constant drying period, the moisture of unbound will finish then the dry spots appears. The constant drying period ends at critical moisture content.

12. After critical moisture content _________ starts.
a) Saturated drying region
b) Unsaturated drying region
c) Constant drying region
d) None of the mentioned

Explanation: After the critical moisture content, the falling period starts which are the unsaturated drying region.

13. After the unsaturated drying completed ________ starts to evaporate.
a) Bound
b) Unbound
c) Equilibrium
d) None of the mentioned

Explanation: After the unsaturated drying the internal movement starts which is the evaporation of bound moisture.

14. Find the representation AB in the batch drying curve.

a) Constant drying region
b) Falling rate period
c) Equilibrium moisture content
d) None of the mentioned

Explanation: The flux remains constant only for constant drying period.

15. Find the point D moisture content.

a) Bound
b) Unbound
c) Equilibrium
d) None of the mentioned

Explanation: At the zero rate, the equilibrium attains the moisture content at that stage is equilibrium moisture content.

Sanfoundry Global Education & Learning Series – Mass Transfer.

To practice all areas of Mass Transfer, here is complete set of 1000+ Multiple Choice Questions and Answers