About Mass Transfer

Do you have a big project that requires moving masses of material? Mass transfer may be the process you need.

Mass transfer is the movement of a substance from one location to another. The process involves transferring both the material and the momentum of the substance.

There are three main types of mass transfer: -

  1. Diffusion
  2. Convection
  3. Radiation

Diffusion is the most common type of mass transfer. It is the movement of particles from an area of high concentration to an area of low concentration. Convection is the movement of particles from one area to another due to a difference in temperature.Radiation is the movement of energy from one place to another.

Mass transfer can be used in a variety of industries, including:

  • Food and beverage
  • Pharmaceutical
  • Cosmetic
  • Chemical

Each industry has different requirements for mass transfer. The food and beverage industry, for example, requires the movement of large quantities of material at a high speed.

The pharmaceutical industry often requires precise control over the movement of materials. The cosmetic and chemical industries require both precision and speed.

Wrapping Up

Mass transfer is a versatile process that can be used to move material quickly and easily. If you have a project that requires moving large quantities of material, consider using mass transfer.

Following are some of the multiple choice questions on the Mass Transfer with answers that will help the students in developing their knowledge.

Mass Transfer MCQ

1. Leaching of coarse solid lumps is also termed as

  • Decoction
  • Dissolution
  • Percolation
  • Agitation and settling

2. Out of two equilibrium curves, first one lies above the diagonal and the second lies below the diagonal in the x-y plot. It means that separation by distillation is

  • Not possible in the second case unless vacuum is applied
  • More readily done in the second case compared to first one
  • Not possible in the second case unless high pressure is applied
  • None of these

3. With increase in temperature, the leaching rate increases because of the

  • Increased diffusivity
  • Decreased viscosity of liquid
  • Both A and B
  • Neither A nor B

4. The most economical range of absorption factor is

  • 0 to 0.5
  • 0 to 3
  • 1.25 to 2
  • 5 to 15

5. Which of the following is an undesirable property in a tower packing?

  • Large surface per unit volume
  • Large free cross-section
  • Low weight per unit volume
  • Large weight of liquid retained

6. Advantage of continuous drying over batch drying is that the

  • Drying cost per unit weight of dried product is less
  • Product with more uniform moisture content is produced
  • Equipment size required is smaller
  • All of the above

7. __________ is the temperature at which a gas-vapor mixture becomes saturated, when cooled at constant total pressure out of contact with a liquid.

  • Dew point
  • Bubble point
  • Dry bulb temperature
  • Wet bulb temperature

8. Channelling in a packed tower results from the

  • High pressure drop
  • Maldistribution of liquid
  • Non-uniformity of packing
  • Both B and C

9. Pick out the wrong statement. Generally for physical adsorption, a gas of

  • Higher molecular weight is adsorbed in preference to a gas of low molecular weight
  • High critical temperature is adsorbed in preference to a gas of low critical temperature
  • Low volatility is adsorbed in preference to a gas of high volatility
  • None of these

10. Dew point of a gas-vapour mixture

  • Increases with temperature rise
  • Decreases with temperature rise
  • Decreases with decrease in pressure
  • Increases with increase in pressure

11. A solid is being dried in the linear drying rate regime from moisture content Xo to XF. The drying rate is zero at X = 0 and the critical moisture content is the same as the initial moisture Xo. The drying time for M = (Ls/ARc) is (where, L = total mass of dry solid, A = total surface area for drying Rc = Constant maximum drying rate per unit area X = moisture content (in mass of water/mass of dry solids)

  • M(Xo - XF)
  • M(Xo/XF)
  • M ln(Xo/XF)
  • MXo ln(Xo/XF)

12. Overall efficiency of the distillation column is

  • The ratio of number of ideal plates to actual plates
  • The ratio of number of actual plates to ideal plates
  • Same as the Murphree efficiency
  • Always more than the point efficiency

13. Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the __________ of a fibre.

  • Electrical resistance
  • Thermal conductivity
  • Strength
  • None of these

14. __________ extractor is used for the concentration of radioactive nuclear waste.

  • Pulsed column
  • Seive plate
  • Mixer-settler
  • Ballman

15. Dew point of an air-water vapor mixture

  • Decreases with decrease in pressure
  • At constant humidity & total pressure is fixed
  • Corresponding to any point on the humidity chart is obtained by projecting a line through this point parallel to the temperature axis and to the saturation curve
  • All of the above

16. In case of a desorber (stripper), the

  • Operating line always lies above the equilibrium curve
  • Operating line always lies below the equilibrium curve
  • Temperature remains unaffected
  • Temperature always increases

17. The ratio of Murphree plate efficiency to point efficiency is always > 1 in a __________ flow model.

  • Plug
  • Perfectly mixed
  • Both A & B
  • Neither A nor B

18. Which of the following equipments is not used for gas dispersion?

  • Agitated vessels
  • Bubble cap tray towers
  • Perforated sieve tray towers
  • Spray towers

19. The relation, Sc = Pr = 1, is valid, when the mechanism of __________ ansfer is same.

  • Heat and mass
  • Mass and momentum
  • Heat and momentum
  • Heat, momentum and mass

20. In case of an absorber, the operating

  • Line always lies above the equilibrium curve
  • Line always lies below the equilibrium curve
  • Line can be either above or below the equilibrium curve
  • Velocity is more than the loading velocity

21. In case of binary distillation, increasing the reflux ratio above optimum does not result in the increase of

  • Area between operating line and 45° diagonal x-y diagram
  • Condenser and reboiler surfaces
  • Tower cross-section
  • None of these

22. The reflux to a distillation column is 100 moles/hr, when the overhead product rate is 50 moles/hr. The reflux ratio is

  • 2
  • 0.5
  • 50
  • 150

23. In a gas-liquid absorption coloumn, for obtaining the maximum absorption efficiency

  • Liquid stream should be distributed uniformly
  • Gas stream should be distributed uniformly
  • Both gas as well as liquid streams should be distributed uniformly
  • By passing should be completely avoided

24. __________ column is the most suitable for achieving the best performance for mass transfer operations involving liquid with dispersed solids.

  • Watted wall
  • Packed
  • Plate
  • Spray

25. The assumption made in Elis method in distillation is that enthalpy concentration lines of vapor and liquid are

  • Parallel
  • Straight
  • Both parallel and straight
  • Neither parallel nor straight

26. If f = moles of vapour present per mole of feed, then the slope of feed line is (Mcabe-Thiele method)

  • (1 - f)/f
  • - (f - 1)/f
  • - 1/f
  • - f/(1 - f)

27. Which of the following employs an accessory known as 'drift eliminator' ?

  • Multiple effect evaporator
  • Mechanical draft cooling tower
  • Rotary dryer
  • Rotating disc contactor

28. Most important factor to be considered in the selection of packings for absorbers is the __________ of packing.

  • Size
  • Durability
  • Porosity
  • Cost

29. 'Absorption with chemical reaction' is involved in the removal of

  • Carbon dioxide from gaseous stream using alkaline solution
  • Benzol from coke oven gas using solar oil/wash oil
  • Ammonia from coke oven gas using refrigerated water
  • Tar from coke oven gas in primary gas coolers using chilled water

30. Laboratory determination of the dif-fusivity of vapor is done by __________ method.

  • Wetted wall column
  • Gilliland's
  • Winkel mann's
  • Wike's

31. Drying of a solid involves __________ transfer.

  • Only heat
  • Only mass
  • Both heat and mass
  • None of these

32. Dryer widely used in a textile industry is __________ dryer.

  • Festoon
  • Cylinder
  • Conveyor
  • Tunnel

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

  • Increases
  • Decreases
  • Remains same
  • Either A or B, depends on the system

34. Which of the following equipments is not used in liquid-liquid extraction?

  • Pachuka tank
  • Agitated vessels
  • Centrifugal extractors
  • Packed towers

35. Even though bubble cap towers are very effective for humidification operation, they are not used commonly in industries, because of the

  • High evaporation losses of water
  • High pressure drop of the gas
  • Difficulty in its fabrication
  • None of these

36. The diffusivity, DAB (for component A diffusing in B) is equal to the diffusivity Dsub>BA (for component B diffusing in A) for a binary mixture of

  • Newtonion liquids
  • Non-Newtonion liquids
  • Ideal gases
  • Real gases

37. For absorbers, high pressure drop results in

  • Increased efficiency
  • Decreased efficiency
  • High operating cost
  • Better gas liquid contact

38. The solvent used in liquid extraction should not have high latent heat of vaporisation, because

  • The pressure drop and hence the pumping cost will be very high
  • It cannot be recovered by distillation
  • Its recovery cost by distillation may be prohibitatively high
  • It will decompose while recovering by distillation

39. Ponchan-Savarit method analyses the fractional equipment based on

  • Enthalpy balance only
  • Material balance only
  • Both enthalpy and material balances
  • The assumption of constant molaloverflow

40. Polar organic compounds are normally used as separating agents for the azeotropic and extractive distillation. Which of the following is the most important factor to be considered for the choice of the separating agent for extractive distillation?

  • Cost
  • Availability
  • Toxicity
  • Selectivity

41. Component A is diffusing in a medium B. The flux NA relative to a stationary point is equal to the flux due to molecular difusion, if

  • Mass transfer is accompanied by reaction
  • Diffusion of A is in stagnant medium B
  • Molecular mean free path is high
  • There is equimolar counter diffusion

42. Calculation of mass transfer co-efficient is mostly/normally done using __________ theory.

  • Surface renewal
  • Film
  • Penetration
  • None of these

43. One mole feed of a binary mixture of a given composition is flash vaporised at a fixed P and T. If Raoult's law is obeyed, then changing the feed composition would effect

  • The product composition but not the fraction vaporised
  • The product composition as well as the fraction vaporised
  • The fraction vaporised but not the product composition
  • Neither the product composition nor the fraction vaporised

44. The recovery of pencillin from the acidified fermentation broth is done by

  • Distillation
  • Evaporation
  • Absorption
  • Liquid extraction

45. Absorption factor, for a fixed degree of absorption from a fixed amount of gas should be

  • 1
  • > 1
  • ≤ 1
  • none of the above

46. Which is not concerned directly with mass transfer?

  • Schmidt number
  • Sherwood number
  • Lewis relationship
  • Froude number

47. The 'shanks system' of leaching (i.e., counter-current multiple contact leaching) is used for

  • Recovery of tannis from the tree barks and woods
  • Leaching sodium nitrate from Chilean nitrate bearing rock
  • Both A & B
  • Neither A nor B

48. Which of the following is directly concerned with psychrometry?

  • Lewis reltionship
  • Galileo number
  • Weber number
  • Dean number

49. With increase in the liquid flow rate at a fixed gas velocity in a randomly packed counter current gas-liquid absorption column, the gas pressure drop

  • Decreases
  • Remains unchanged
  • Increases
  • Decreases exponentially

50. Flooding in a distillation column is detected by a sharp

  • Increase in Murphree plate efficiency
  • Decrease in pressure drop
  • Decrease in liquid hold up in the coloumn
  • Increase in pressure drop

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