Mass Transfer Indiabix 1 - 5

1. Mass transfer rate between two fluid phases does not necessarily depend

on the __________ of the two phases.

a. chemical properties

b. physical properties

c. degree of turbulence

d. interfacial area

A

2. In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the

molality is

a. 0.50

b. 0.60

c. 2

d. 1

A

3. Fenske equation determines the

a. maximum number of ideal plates.

b. height of the distillation column.

c. minimum number of theoretical plates.

d. optimum reflux ratio

C

4. The term "co" in a cooling tower refers to the difference in the temperature

of

a. cold water leaving the tower and the wet bulb temperature of the

surrounding air.

b. hot water entering the tower and the wet bulb temperature of the

surrounding air.

c. hot water entering the tower and the cooled water leaving the

tower.

d. none of these

C

5. Which of the following is the most suitable for extraction in a system

having very low density difference?

a. Mixer-settler extractor

b. Centrifugal extractor

c. Pulsed extractor

d. Packed extraction tower

B

6. Total reflux in a distillation operation requires minimum

a. reboiler load

b. number of plates

c. condenser load

d. all (a), (b) and (c)

B

7. The amount of steam required per unit quantity of distillate in case of steam

distillation will be reduced by

a. raising the temperature.

b. lowering the total pressure.

c. both (a) and (b).

d. neither (a) nor (b)

C

8. The difference of wet bulb temperature and adiabatic saturation temperature

of unsaturated mixture of any system is

a. +ve

b. -ve

c. zero

d. none of these

A

9. Fenske's equation for determining the minimum number of theoretical

stages in distillation column holds good, when the

a. relative volatility is reasonably constant.

b. mixture (to be separated) shows negative deviation from ideality.

c. mixture (to be separated) shows positive deviation from ideality.

d. multicomponent distillation is involved.

A

10. When the temperature and humidity of air is low, we usually use

__________ draft cooling tower.

a. natural

b. forced

c. induced

d. none of these

A

11. Pick out the correct statement.

a. In case of liquid-liquid extraction, no separation is possible, if the

selectivity of the solvent used is unity.

b. With increase in temperature, the selectivity of the solvent used in

solvent extraction decreases.

c. The selectivity of solvent used in solvent extraction is unity at the

plait point.

d. all (a), (b) and (c).

D

12. __________ columns are used for liquid dispersion in a continuous gas

phase.

a. Packed

b. Pulse

c. Bubble cap

d. Sieve plate

A

13. Overall efficiency of the distillation column is

a. the ratio of number of ideal plates to actual plates.

b. the ratio of number of actual plates to ideal plates.

c. same as the Murphree efficiency.

d. always more than the point efficiency.

A

14. On addition of solute in the solvent, the __________ of the solution

decreases.

a. boiling point

b. freezing point

c. vapour pressure

d. both (b) and (c)

D

15. Which is the controlling factor for a drum drier?

a. Diffusion

b. Heat transfer

c. Both (a) and (b)

d. Neither (a) nor (b)

B

16. Drying operation under vacuum is carried out to

a. dry those materials which have very high unbound mositure

content.

b. reduce drying temperature.

c. increase drying temperature.

d. dry materials having high bound moisture content.

B

17. Air initially at 101. 3 kPa and 40°C and with a relative humidity of 50%, is

cooled at constant pressure to 30°C. The cooled air has a

a. higher dew point.

b. higher absolute (specific) humidity.

c. higher relative humidity

d. higher wet bulb temperature.

C

18. Separation of two or more components of a liquid solution can not be

achieved by

a. fractional crystallisation

b. liquid extraction

c. absorption

d. evaporation

C

19. Stefan's law describes the mass transfer by

a. diffusion

b. bulk flow

c. both 'a' & 'b'

d. neither 'a' nor 'b'

C

20. At minimum reflux ratio for a given separation

a. number of plates is zero.

b. number of plates is infinity.

c. minimum number of the theoretical plates is required.

d. separation is most efficient.

B

21. Relative humidity is the ratio of the

a. partial pressure of the vapour to the vapour pressure of the liquid at

room temperature.

b. partial pressure of the vapour to the vapour pressure of the liquid at

gas temperature.

c. actual humidity to saturation humidity.

d. none of these

B

22. In batch distillation with constant reflux, overhead product composition

__________ with time.

a. increases

b. decreases

c. does not vary

d. may increase on decrease, depends on the system.

B

23. Psychrometry deals with the properties of gas-vapor mixture. Humidity

can be determined by the measurement of the __________ of a fibre.

a. electrical resistance

b. thermal conductivity

c. strength

d. none of these.

A

24. Heat in BTU necessary to increase the temperature of 1 lb of gas and its

accompanying vapour by 1°F is called the

a. latent heat

b. humid heat

c. specific heat

d. sensible heat

C

25. To increase the absorption factor, (where, G = gas flow rate, S = solvent

flow rate)

a. increase both 'G' and 'S'.

b. decrease both 'G' and 'S'.

c. increase 'S' and decrease 'G'.

d. increase 'G' and decrease 'S'

C

26. The mass diffusivity, the thermal diffusivity and the eddy momentum

diffusivity are same for, NPr = NSc = __________

a. 1

b. 0.5

c. 10

d. 0

A

27. Dew point of a gas-vapour mixture

a. increases with temperature rise.

b. decreases with temperature rise.

c. decreases with decrease in pressure.

d. increases with increase in pressure.

C

28. In a packed absorption tower, if the equilibrium and operating lines are

both straight lines, then the ratio, HETP/HTUOG __________ the absorption

factor.

a. increases with increase in

b. is one at unity value of

c. both (a) and (b)

d. neither (a) nor (b)

C

29. Which of the following plays an important role in problems of

simultaneous heat and mass transfer ?

a. Lewis number

b. Schmidt number

c. Prandtl number

d. Sherwood number

A

30. In case of an absorber, the operating

a. line always lies above the equilibrium curve.

b. line always lies below the equilibrium curve.

c. line can be either above or below the equilibrium curve

d. velocity is more than the loading velocity.

A

31. As the reflux ratio in a distillation coloumn is increased from the

minimum, the

a. slope of the operating line in stripping section decreases.

b. number of plates decreases very slowly first and then more and

more rapidly.

c. total cost first decreases and then increases.

d. liquid flow increases while the vapor flow decreases for a system.

C

32. Absorption factor is defined as (where, S1 = slope of the operating line S2

= slope of the equilibrium curve)

a. S2/S1

b. S1/S2

c. S1 - S2

d. S1 x S2

B

33. A plait point is the point on the solubility curve, where the tie line reduces

to a point. What is the number of plait point for a ternery system containing

twopairs of partially miscible liquids?

a. 0

b. 1

c. 2

d. 3

A

34. Which of the following remains constant during sensible cooling process ?

a. Specific humidity

b. Partial pressure of vapour

c. Both (a) and (b)

d. Neither (a) nor (b)

C

35. Physical absorption is

a. an irreversible phenomenon.

b. a reversible phenomenon.

c. accompanied by evolution of heat.

d. both (b) and (c)

D

36. Make up water is required in a cooling tower to replace the water lost by

a. evaporation

b. drift

c. blowdown and leakage

d. all (a), (b) and (c)

D

37. Which of the following quantities need not be fixed before starting the

design of a co-current absorber?

a. Heat gain or loss

b. Flow rate of entering liquid

c. Flow rate of gas

d. None of these

B

38. Mass transfer co-efficient of liquid is

a. affected more by temperature than that for gases.

b. affected much less by temperature than that for gases.

c. not affected by the temperature.

d. none of these.

A

39. Absorption accompanied with chemical reaction is exemplified by the

absorption of

a. ammonia in water.

b. benzol present in coke oven gas by wash oil.

c. SO2 in alkaline solution.

d. all (a), (b) and (c).

C

40. Which of the following unit operations makes use of Thiele-Geddes

equation ?

a. Liquid-liquid extraction

b. Solid-liquid extraction

c. Multicomponent absorption with chemical reaction

d. Multicomponent distillation.

D

41. Which of the following liquid-vapor contacting devices provides

maximum contact surface area for a particular duty?

a. Sieve plate column

b. Bubble cap column

c. Randomly packed column

d. Wetted wall column

D

42. The equipment frequently used for adiabatic humidification-cooling

operation with recirculating liquid is

a. natural draft cooling tower

b. induced draft cooling tower

c. spray chamber

d. none of these

C

43. Chemisorption (chemical adsorption) is

a. same as "Van der Waals" adsorption.

b. characterised by adsorption of heat.

c. an irreversible phenomenon.

d. a reversible phenomenon.

C

44. The rate of solid-liquid extraction is limited by the

a. phase change of the solute as it dissolves in the solvent.

b. diffusion of the solute through the solvent in the pores to the

outside of the particle.

c. diffusion of the solute from the solution in contact with the particle

to the main bulk of the solution.

d. all 'a', 'b' & 'c'.

D

45. Raoult's law applies to the

a. all liquid solutions

b. non-ideal solution only.

c. non-volatile solute.

d. solvents.

D

46. In distillation columns, the number of bubble caps per tray primarily

depends upon the

a. allowable liquid velocity.

b. allowable gas velocity.

c. allowable gas and liquid velocities.

d. feed composition.

C

47. In distillation, overhead product contains

a. only one component

b. two components

c. any number of components

d. only saturated liquid

C

48. With increase in pressure, the relative volatility for a binary system

a. increases.

b. decreases.

c. remains same.

d. either (a) or (b), depends on the system.

B

49. Low viscosity absorbent is preferred for reasons of

a. rapid absorption rates and good heat transfer characteristics.

b. improved flooding characteristics.

c. low pressure drop on pumping.

d. all (a), (b) and (c).

D

50. Mass transfer co-efficient (K) and diffusivity (D) are related according to

film theory as

a. K ∝ D

b. K ∝(D)^1/2

c. K ∝ D1.5

d. K ∝ D2

A

1. The McCabe Δ L law states that the

a. molar heats of vaporisation of components are nearly equal.

b. linear crystal growth rate depends on the degree of supersaturation.

c. linear crystal growth rate does not depend on the crystal size.

d. linear crystal growth rate depends on the crystal size.

C

2. Bollman extractor

a. is a static bed leaching equipment.

b. is used for extraction of oil from oilseed.

c. is a centrifugal extractor.

d. employs only counter-current extraction.

B

3. The relation, Sc = Pr = 1, is valid, when the mechanism of __________

ansfer is same.

a. heat and mass

b. mass and momentum

c. heat and momentum

d. heat, momentum and mass

A

4. A coalescer in a mixer-settler liquid-liquid extraction coloumn

a. comprises of thin bed of substances of extended surface having

high porosity.

b. helps in increasing the bubble size entering the settler.

c. helps in increasing the settling rate of the bubbles.

d. all 'a', 'b', & 'c'.

D

5. For the same feed, feed quality and separation (in a distillation column),

with the increase of total pressure, the number of ideal plates will

a. increase

b. decrease

c. remain same

d. data insufficient, can't be predicted

A

6. Pick out the correct statement.

a. Ponchan-Savarit method is more accurate than McCabe-Thiele

method to determine the number of theoretical stages required for

the separation of non-ideal binary system by distillation.

b. A sharp decrease in pressure drop is an indication of flooding in a

distillation coloumn.

c. Solvent used in extractive distillation should be of high volatility.

d. Flash distillation is suitable for separating components which have

very close boiling temperature

A

7. When the liquid phase and vapour phase of a binary system obeys Raoult's

and Dalton's law respectively, the relative volatility is the ratio of

a. vapour pressure of component A to that of component B.

b. vapour pressure of component A to the total pressure.

c. vapour pressure of component A to the partial pressure of A.

d. partial pressure of component A to the total pressure

A

8. The operation involved when the soluble material is largely on the surface

of an insoluble solid and is merely washed off by the solvent is called

a. decoction

b. percolation

c. elutriation or elution

d. none of these

C

9.In the constant rate period of the rate of drying curve for batch drying,

a. cracks develop on the surface of the solid.

b. rate of drying decreases abruptly.

c. surface evaporation of unbound moisture occurs.

d. none of these.

C

10. It takes 6 hours to dry a wet solid from 50% moisture content to the

critical moisture content of 15%. How much longer it will take to dry the solid

to 10% moisture content, under the same drying conditions? (The equilibrium

moisture content of the solid is 5%).

a. 15 min

b. 51 min

c. 71 min

d. 94 min

C

11. Agitator is provided in a crystalliser for

a. avoiding deposition on cooler surfaces.

b. formation of nuclei.

c. crystal growth.

d. all (a), (b) and (c).

D

12. __________ diffusion is used for separating the isotopes of methane.

a. Thermal

b. Pressure

c. Concentration

d. Force

A

13. Ordinary diffusion process is also called __________ diffusion.

a. pressure

b. thermal

c. concentration

d. forced.

C

14. Pick out the wrong statement.

a. Different solids have different equilibrium moisture curves.

b. Total condenser or reboiler is considered equivalent to one

theoretical plate in McCabe-Thiele method of theoretical plate

calculation for distillation column.

c. Heat removal load on cooler remains constant, even with increase

of the reflux ratio in a distillation column.

d. Even a forced draft cooling tower can not cool water below the wet

bulb temperature

C

15. Pick out the wrong statement pertaining to the rotary dryer.

a. Flights (located in the inside shell of rotary dryer) lift the material

being dried and shower it down through the current of hot

air/gases. It extends from the wall to a distance which is about 8-

12% of the inside diameter of shell.

b. Hold up of a rotary drier is defined as the fraction of the dryer

volume occupied by the solid at any instant. The best performance

for rotary drier is obtained, when the hold up is in the range of 0.05

to 0.15.

c. Rotary dryer is suitable for drying sticky material.

d. Recommended peripherial speed of a rotary drier is in the range of

10 to 30 metres/minute.

C

16. The reason for preferring packed towers over plate towers in distillation

practice is that the packed tower operation gives

a. low pressure drop and high hold up.

b. high pressure drop and low hold up.

c. low pressure drop and low hold up.

d. high pressure drop and high hold up.

C

17. If the path of liquid across the plate is very long as in case of large

diameter tower, Murphree efficiency can be __________ percent.

a. 100

b. >100

c. < 100

d. none of these

B

18. Compound A is extracted from a solution of A + B into a pure solvent S. A

Co-current unit is used for the liquid-liquid extraction. The inlet rate of the

solution containing A is 200 moles of B/hr.m2 and the solvent flow, rate is 400

moles of S/m2. hr. The equilibrium data is represented by Y = 3X2 , where Y

is in moles of a A/moles of B and X is in moles A/moles of S. The maximum

percentage extraction achieved in the unit is

a. 25%

b. 50%

c. 70%

d. 90%

B

19. Raoult's law is applicable to the

a. ideal solutions

b. real solutions

c. mixture of water and alcohol

d. non-ideal gases

A

20. Weeping in a distillation column

a. increases tray efficiency.

b. provides large interfacial surface for mass transfer.

c. results due to very high gas velocity.

d. results due to very low gas velocity.

D

21. In case of binary distillation, increasing the reflux ratio above optimum

does not result in the increase of

a. area between operating line and 45° diagonal x-y diagram.

b. condenser and reboiler surfaces.

c. tower cross-section.

d. none of these.

A

22. Wetted wall tower experiment determines the

a. molal diffusivity.

b. volumetric co-efficient.

c. mass transfer co-efficient.

d. none of these.

C

23. In McCabe-Thiele method, at infinite reflux ratio

a. the overhead product is minimum.

b. both the operating lines coincide with diagonal.

c. both (a) and (b).

d. neither (a) nor (b).

A

24. With decrease in the throughput (compared with the design capacity) for a

bubble cap distillation column, its efficiency

a. increases

b. decreases

c. remains same

d. may increase or decrease; depends on individual design.

A

25. Plate towers are preferred to packed towers, when large temperature

changes are involved, because of the reason that the

a. packing may be crushed due to thermal expansion/contraction of

the components of the equipments.

b. pressure drop in the equipment will be . very high.

c. viscosity variation of the fluids may cause channeling/flooding.

d. none of these.

A

26. The equilibrium liquid composition compared to the vapor composition in

case of azeotropic mixture is

a. more

b. less

c. same

d. either more or less; depends on the system

C

27. Out of the following gas-liquid contacting devices, for a given set of

operating conditions, gas pressure drop is the least in __________ tower.

a. wetted wall

b. bubble cap

c. perforated tray

d. packed

A

28. Pick out the system with minimum boiling azeotrope at 1 atm.

a. benzene-toluene

b. ethyl alcohol-water

c. hydrochloric acid-water

d. all (a), (b) and (c)

B

29. Free flowing granular materials can be best dried in a __________ drier.

a. rotary

b. cylinder

c. drun

d. freeze

A

30. In case of an ideal solution, the total vapor pressure varies __________

with the composition expressed as mole fraction,

a. inversely

b. linearly

c. exponentially

d. none of these

B

31. Corresponding to Nusselt number in heat transfer, the dimensionless group

in mass transfer is the __________ number.

a. Sherwood

b. Schmidt

c. Peclet

d. Stanton

A

32. If the specific heats of a gas and a vapor are 0.2KJ/Kg.°K and 1.5

KJ/Kg.°K respectively, and the humidity is 0.01; the humid heat in KJ/°Kg. is

a. 0.31

b. 0.107

c. 0.017

d. 0.215

D

33. Liquid diffusivity is of the order of __________ cm2 /second.

a. 0.01

b. 0.1

c. 10^-5 to 10^-6

d. > 1

C

34. The solvent used in liquid extraction should not have high latent heat of

vaporisation, because

a. the pressure drop and hence the pumping cost will be very high.

b. it cannot be recovered by distillation.

c. its recovery cost by distillation may be prohibitatively high.

d. it will decompose while recovering by distillation.

C

35. At the same gas flow rate, the pressure drop in a packed tower being

irrigated with liquid __________ that in dry packed tower.

a. is greater than

b. is lower than

c. is same as

d. cannot be predicted as data are insufficien

A

36. Molarity is defined as the number of gm moles of solute per __________

of solvent.

a. litre

b. kg

c. gm

d. c.c

A

37. The value of Lewis number (Le = Sc/Pr) for air-water vapour system is

around

a. 1

b. 0.24

c. 3.97

d. 600

A

39. An aqueous solution of methanol is to be distilled in a tray column. High

pressure steam is available as a source of heat. For a given reflux ratio and

overhead composition, two options are being explored; (i) a reboiler is used

and (ii) no reboiler is used but steam is fed directly to the bottom of the

column. As compared to option (i), in option (ii)

a. less number of trays are required.

b. composition of the residue remains unchanged.

c. more number of trays are required but the residue composition

remains unchanged.

d. more number of trays are required and the residue composition is

more dilute in methanol.

A

40. The partial pressure distribution of an ideal gas diffusing through another

stagnant ideal gas at steady state follows a/an __________ law.

a. exponential

b. parabolic

c. linear

d. cubic

A

41. Which of the following binary systems is an example of a maximum

boiling azeotrope ?

a. Water-hydrochloric acid.

b. Acetone-carbon disulphide.

c. Water-ethyl alcohol.

d. n-heptane-n-octane

A

42. (NRe . NSc) is termed in mass transfer operation as the __________

number.

a. Stanton

b. Sherwood

c. Peclet

d. none of these

C

43. The binary diffusivity in gases and liquids vary respectively as

a. T

3/2 and T

b. T and T3/2

c. T

1/2 and T3/2

d. T

3/2 and T1/2

A

44. Pick out the correct statement.

a. The slope of the stripping line is always less than unity.

b. For a given separation in a binary distillation column, with increase

in reflux ratio (above the minimum reflux ratio), the fixed cost of

the distillation column first increases and then decreases.

c. In Ponchon-Savarit method of no. of theoretical plate

determination, the stripping and rectifying operating lines are

vertical at total reflux.

d. Kremsor-Brown-Souder's equation is used to calculate the

efficiency of a plate tower.

C

45. Pick out the correct statement.

a. Dialysis process is used for the production of fresh water from

brine.

b. Electrodylsis is used in the manufacture of NaOH.

c. Electrodylsis is used for the refin-ning/purification of petrol.

d. both (b) and (c).

B

46. Pick out the correct statement.

a. Bound moisture is removed during constant rate drying period.

b. Free moisture is removed during falling rate drying period.

c. The sum of free moisture and equilibrium moisture in a solid is

called the critical moisture.

d. The driving force for mass transfer in a wet solid is its free

moisture content.

D

47. Very tall packed towers are divided into series of beds to

a. reduce the overall pressure drop

b. avoid channelling

c. reduce liquid hold-up

d. avoid flooding

B

48. Moisture contained by a substance in excess of the equilibrium moisture is

called the __________ moisture.

a. unbound

b. free

c. critical

d. bound

B

49.With increase in temperature, the solubility of gases in liquids, at fixed

pressure

a. increases

b. decreases

c. remains same

d. either (a) or (b), depends on the system.

B

50. In most of the vacuum crystalliser, vacuum is generally produced by

means of a

a. suction pump

b. compressed air jet

c. steam jet ejector with a barometric condenser

d. none of these

C

1. On moving the feed line (q-line) from saturated liquid feed (vertical

position) to saturated vapor feed (horizontal feed), if the slope of both the

operating lines are to be increased, then it will result in

a. greater degree of separation with a fixed number of trays

b. increased reboiler load

c. increased reflux ratio

d. None of these

C