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 ______________________?
comments icon0

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?
comments icon0
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_______________________?
comments icon0

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 _____________________?
comments icon0

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) ______________________?
comments icon0
A. ?T

B. T

C. T2

D. T4

6. The cooling effect in a cooling tower can be speeded up by _______________________?
comments icon0

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 ?
comments icon0
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 _________________________?
comments icon0

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___________________?
comments icon0

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) ?
comments icon0

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 ?
comments icon0
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__________________?
comments icon0
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 ?
comments icon0

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 ?
comments icon0

A. 28

B. 9

C. 12

D. 5

15. _______________ equation applies to diffusivities in liquids?
comments icon0

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?
comments icon0

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_______________________?
comments icon0
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_____________________?
comments icon0

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?
comments icon0

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?
comments icon0

A. Mixture of two gases

B. Ideal gas

C. Pure gas

D. Sparingly soluble gas

21. The commonly used solvent in supercritical extraction is_____________________?
comments icon0

A. Carbon tetrachloride

B. Methyl ethyl ketone

C. Carbon dioxide

D. Water

22. Cox chart, which is useful in the design of distillation column particularly for petroleum hydrocarbons, is a plot of (where, P = vapor pressure, T = temperature) ?
comments icon0

A. T vs. P

B. log P vs. log T

C. log P vs. T

D. P vs. log T

23. Large scale drying of sugar is done in a _______________ dryer?
comments icon0

A. Truck

B. Tray

C. Rotary

D. Spouted bed

24. ___________________ extractor uses centrifugal force for separating the two phases?
comments icon0
A. Podbielniak

B. Treybal

C. Scheibel

D. None of these

25. To get high tray efficiency___________________?
comments icon0

A. Time of contact between the two phases should be less

B. Liquid entrainment should be severe

C. Interfacial surface between liquid and gas phase should be large

D. Gas velocity should be very low

26. At what percentage (by volume) of alcohol composition, it forms an azeotrope with water ?
comments icon0

A. 99

B. 91.5

C. 90

D. 95
27. In rectifying section of a continuous distillation column, the____________________?
comments icon0
A. Vapour is enriched with high boilers

B. Vapour is enriched with low boilers

C. None of these

D. Liquid is stripped of high boilers

28. Molality is defined as the number of gm moles of solute per _________________ of solvent ?
comments icon0

A. Litre

B. gm

C. Kg

D. m3

29. Absorption (liquid-gas system) with evolution of heat as compared to isothermal absorption results in_________________?
comments icon0

A. Large number of trays

B. Large minimum liquid to gas (L/G) ratio

C. Decreased solute solubility

D. All A., B. and C.
30. Paper industry employs _______________ driers?
comments icon0

A. Spray

B. Cylinder

C. Rotary

D. Fluidised bed

31. Removal of ______________ exemplifies an adsorption unit operation?
comments icon0

A. Ammonia from coke oven gas

B. Water from petrol

C. Mustard oil from mustard seed

D. Uranium from its ore

32. For stripping of a gas in a counter current stripper, the operating line _____________________?
comments icon0

A. Lies below the equilibrium curve

B. Is always parallel to the equilibrium curve

C. Lies above the equilibrium curve

D. Can lie above or below the equilibrium curve
33. With increase in temperature, the leaching rate increases because of the _____________________?
comments icon0

A. Increased diffusivity

B. Decreased viscosity of liquid

C. Both A. and B.

D. Neither A. nor B.

34. Plate efficiency in a distillation column is reduced due to the ______________ of liquid?
comments icon0
A. All A., B. & C.

B. Foaming

C. Entrainment

D. Weeping & dumping

35. Separation of two volatile liquids by distillation makes use of their________________________?
comments icon0
A. Relative volatility

B. Selectivity

C. Density difference

D. Solubility

36. Mechanism of moisture removal in case of freeze drying of food stuff is by ___________________?
comments icon0

A. Adsorption

B. Dehydration

C. Sublimation

D. Evaporation

37. Which of the following provides maximum contact surface for a liquid-vapour system ?
comments icon0

A. Wetted wall column

B. Packed tower

C. Sieve-plate column

D. Bubble-cap plate column

38. The minimum liquid rate to be used in an absorber corresponds to an operating line__________________?
comments icon0

A. Of slope = 1

B. Tangential to the equilibrium curve

C. Of slope = 0.1

D. None of these

39. Minimum reflux ratio in a distillation column results in_____________________?
comments icon0

A. Optimum number of trays

B. Minimum number of trays

C. Minimum reboiler size

D. Maximum condenser size
40. Measurement of the interfacial area of mass transfer is achieved easily & accurately in case of a ________________ column?
comments icon0

A. Packed

B. Wetted wall

C. Bubble cap plate

D. Spray

41. Dorr thickener is an equipment used for___________________?
comments icon0

A. Classification

B. Clarification

C. Sedimentation

D. Leaching

42. Mass transfer co-efficient is directly proportional to DAB according to the _____________ theory?
comments icon0
A. Film

B. Penetration

C. None of these

D. Surface-renewal

43. Plate efficiency in a distillation column is reduced due to the ______________________ of liquid?
comments icon0

A. Foaming

B. Entrainment

C. Weeping & dumping

D. All A., B. & C.
44. The velocity, concentration and temperature boundary, for the boundary layer development on a flat plate during connective mass transfer will be same, if___________________?
comments icon0

A. NSc = NLe

B. NPr = NLe

C. NSc = NPr = NLe

D. NSc = 1

45. Penetration theory states that the mass transfer co-coefficient is equal to (where, De is diffusivity and t is time) ?
comments icon0

A. (De.t)1/2

B. (4De/?t)1/2

C. (4De/t)

D. (De/t)1/2

46. Can the efficiency of a plate in the distillation tower be greater than 100% ?
comments icon0
A. Never

B. Yes; if the reflux ratio is maximum

C. Yes

D. Normally not; but is possible if infinite number of plates are put

47. The boiling points of pure components of a binary system ________________ with increase in total pressure of the system ?
comments icon0

A. May increase or decrease, depends on the system

B. Remains unchanged

C. Increases

D. Decreases

48. The operating cost of a distillation column at minimum reflux ratio is____________________?
comments icon0

A. Infinite

B. Maximum

C. Zero

D. Minimum
49. To get high tray efficiency___________________?
comments icon0

A. Time of contact between the two phases should be less

B. Liquid entrainment should be severe

C. Gas velocity should be very low

D. Interfacial surface between liquid and gas phase should be large
50. The humid volume may be increased by increasing the____________________?
comments icon0

A. Temperature at constant humidity

B. Humidity at constant temperature

C. Both A. and B.

D. Neither A. nor B.