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chemical engineering mass transfer MCQs

Practise multiple-choice questions from chemical engineering mass transfer for competitive examinations and subject revision. Review each marked answer and report any item that may be outdated or unclear.

chemical engineering mass transfer Mcqs
1. H2S is being absorbed in a gas absorber unit. The height of the transfer unit based on the overall mass transfer coefficient on the gas side is 0.4 m. The equilibrium data is given by, y = 1.5 x. The bulk concentration of H2S has to be reduced from 0.05 to 0.001 mole fraction in the gas side. The height of the tower (in meters) corresponding to an operating line given by, y = 5x + 0.001 is ______________________?
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A. 1

B. 0.56

C. 2.0

D. 1.56

2. The relative volatility of a binary mixture at constant temperature _________________ the total pressure?
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A. Decreases with increase in

B. None of these

C. Increases with increase in

D. Is independent of

3. The equation, NA = (DAB . Pt /RTZ . PBM) (PA1 PA2) is for_______________________?
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A. Liquid M.T.C. by Higbie penetration theory

B. Steady state diffusion for stagnant case

C. Ficks second law of diffusion

D. None of these

4. The mass transfer co-efficient for a solid sphere of radius a dissolving in a large volume of quiescent liquid, in which D is the diffusivity of solute, is _____________________?
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A. Proportional to ?D

B. D/2a

C. Dependent on the Reynolds number

D. D/a

5. The Knudsen diffusivity is proportional to (where, T = absolute temperature) ______________________?
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A. ?T

B. T

C. T2

D. T4

6. The cooling effect in a cooling tower can be speeded up by _______________________?
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A. Reducing the barometric pressure

B. Reducing the humidity of the air

C. Increasing the air velocity and area of exposed wet surface

D. All A., B. and C.
7. Which of the following processes is not an example of adsorption applied to gaseous separations ?
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A. Decolouration of yellow glycerine

B. Dehumidification of air and gas

C. Removal of objectionable odour and impurities from industrial gases

D. Recovery of valuable solvent vapors from dilute mixture with air and other gases

8. Experiments were conducted to determine the flux of a species A in a stagnant medium across a gas-liquid interface. The overall mass transfer co-efficient based on the liquid side for dilute systems for the above was estimated to be 4 10-3 kg mole/m2.s. The equilibrium data for the system is given as y = 2x. The flux across the interface (in kg mole/m2 .s) for bulk concentrations of A in gas phase and liquid phase as y = 0.4 and x = 0.01 respectively is _________________________?
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A. 8.5 10-3

B. 5.6 10-4

C. 5.6 10-3

D. 8.5 10-4
9. Humidification involves mass transfer between a pure liquid phase and a fixed gas, which is___________________?
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A. Non-ideal in nature

B. Soluble in the liquid

C. At a fixed temperature

D. Insoluble in the liquid
10. For the gas absorption, the height of a transfer unit, based on the gas phase is given by (G: superficial molar gas velocity, L: superficial molar liquid velocity, FG: mass transfer co-efficient, moles/m2, a: interfacial area per unit volume of tower) ?
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A. FG/(G . a)

B. L/(FG . G)

C. G/(FG . a)

D. (G . a)/FG

11. Pore size of the molecular sieve 5A is ____________________ mm ?
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A. 0.5

B. 50

C. 0.05

D. 5

12. For the same system, if the same liquid used in an absorber is decreased, the tower height will__________________?
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A. Increase

B. Remain unaffected

C. Decrease

D. Decrease or increase; depends on the type of liquid

13. During the constant rate period of drying of a solid ?
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A. Increased air humidity decreases the rate of drying

B. None of these

C. Surface evaporation of unbound moisture occurs

D. Increasing the air temperature decreases the drying rate

14. According to the Fenske equation, what will be the minimum number of plates required in a distillation column to separate an equimolar binary mixture of components A and B into an overhead fraction containing 99 mol% A and a bottom fraction containing 98 mol% B ? Assume that relative volatility (?AB = 2) does not change appreciably in the column ?
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A. 28

B. 9

C. 12

D. 5

15. _______________ equation applies to diffusivities in liquids?
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A. Wilke and Chang

B. Gilliland

C. None of these

D. Hirschfelder

16. A natural draft cooling tower is filled with wooden grids, which covers about _________________ percent of the tower height?
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A. 70-80

B. 10-15

C. 90-100

D. 30-40

17. As the reflux ratio, in a continuous counter-current extraction is increased, the number of stages_______________________?
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A. Decrease

B. Can either increase or decrease, depends on the system

C. Remain unchanged

D.
18. Perforated plate towers are unique for solvent extraction because, they provide_____________________?
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A. Better contact of the phase

B. None of these

C. Higher contact area

D. Repeated coalescence & redispersion of the drop phase
19. To remove all the moisture from a wet solid it requires exposure to _____________ air?
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A. None of these

B. Perfectly dry

C. High temperature

D. Highly humid

20. When the gas to be dissolved in liquid is a/an ___________________ then normally co-current adsorber are used?
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A. Mixture of two gases

B. Ideal gas

C. Pure gas

D. Sparingly soluble gas