# Mass Transfer Questions and Answers – Gas-Liquid Equipments

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This set of Mass Transfer Multiple Choice Questions & Answers (MCQs) focuses on “Gas-Liquid Equipments”.

1. For the multistage counter current gas dispersed operation, which of the following equipment is better?
a) Agitated vessel
b) Sparged vessel
c) Tray tower
d) Wetted wall column

Explanation: For the increased extent of the mass transfer tray tower is the best equipment for gas dispersion.

2. During gas dispersion, if a chemical reaction between gas and liquid phase is needed, then the preferred equipment is
a) Agitated vessel
b) Sparged vessel
c) Tray tower
d) Wetted wall column

Explanation: For a reaction to occur we need agitation for a perfect mixing between two phases.

3. The fraction of volume occupied by the gas-liquid mixture in the equipment/vessel to the volume occupied by the gas is
a) Liquid holdup
b) Gas holdup
c) Gas-liquid holdup
d) None of the mentioned

Explanation: The gas holdup gives the fraction of gas in the gas-liquid mixture.

4. In a Sparged vessel of area 50 cm, the flow rate of the gas is 2 cubic meters per second then the value of superficial gas velocity in meters per second is
a) 1
b) 2
c) 3
d) 4

Explanation: Superficial gas velocity = (Volume flow rate/ cross sectional area)
Superficial gas velocity= (2/0.5) =4.

5. In sparged vessel of area 50 cm and a gas holdup of 3 cubic meters per cubic meters, the flow rate of the gas is 5 cubic meters per second. The value of true gas velocity in meters per second is
a) 1.11
b) 2.22
c) 3.33
d) 4.44

Explanation: Superficial gas velocity= (5/0.5)= 10
True gas velocity = Superficial velocity/ gas hold up
=10/3 = 3.33.

6. Guess the diameter of the bubble for an air-water system in a sparged vessel with gas holdup of 0.1 and liquid flow rate of 0.15 meters per second.
a) 7.786 x10-3
b) 7.786 x10-4
c) 9.832 x10-3
d) 9.832 x10-4

Explanation: For a sparged vessel, the diameter of the bubble = (2.344 x10-3)/(Relative velocity of the liquid upwards)0.67
The relative velocity of the liquid upward= liquid flow rate/ (1- gas holdup)
Relative velocity = 0.15/0.9
Diameter = 7.786 x10-3.

7. In a Bubble column, if the velocity of the gas is low, then the bubble diameter is equals to______
a) Vessel
b) Sparger orifice
c) Volume of vessel/ interfacial area
d) None of the mentioned

Explanation: In sparged vessel or bubble column, the gas is dispersed into liquid through the orifice. So for a low gas velocity the diameter of the bubble will be similar to orifice diameter.

8. If the relative velocity of the gas and liquid inside the bubble column of cross sectional area 0.2 meters with gas holdup of 0.736 is 3.6 meters square per second. The expected slip velocity is
a) 3.6 m/s
b) 4.89 m/s
c) 7.2 m/s
d) 9.78 m/s

Explanation: The slip velocity is the relative velocity of both liquid and gas.

9. Guess the interfacial area of a bubble with a gas volume of 2.5 x10^-3 cubic meters and diameter of 0.125 cm.
a) 2 sq.m
b) 4 sq.m
c) 6 sq.m
d) 12 sq.m

Explanation: As the bubble is a sphere, the surface area is (6 x volume)/diameter
Interfacial area= (6 x 2.5 x10^-3)/ 0.00125= 12 sq.m

10. Find the process where an agitated vessel is required.
a) Vegetable oil hydrogenation
b) Production of penicillin
c) Paper stock chlorination
d) All of the mentioned

Explanation: In the given examples, the chemical reaction is required for the product formation. Therefore, the agitation vessel is needed for all the examples mentioned.

11. For a better stage efficiency, must have large interfacial surface and low mass transfer co-efficient.
a) True
b) False

Explanation: The turbulence intensity should be high for a better efficiency. For that, the mass transfer co-efficient should be high.

12. The higher difference in pressure inside the tray tower cause
a) Flooding
c) Weeping
d) Dumping  