1. 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 (αAB = 2) does not change appreciably in the column.
Correct : C. 12
2. With increase in the mass velocity of the gas, the rate of drying during the constant rate period __________, if the conduction and radiation through the solid are negligible.
Correct : A. Increases
3. During the constant rate period of drying of a solid,
Correct : C. Surface evaporation of unbound moisture occurs
4. Large scale drying of wheat is done in a __________ dryer.
Correct : B. Spouted bed
5. Humidification involves mass transfer between a pure liquid phase and a fixed gas, which is
Correct : A. Insoluble in the liquid
6. With increase in temperature, the leaching rate increases due to
Correct : C. Both (A) and (B)
7. As the reflux ratio, in a continuous counter-current extraction is increased, the number of stages
Correct : B. Decrease
8. In distillation where q is defined as the moles of liquid flow in the stripping section per mole of feed introduced, for saturated liquid feed
Correct : C. q = 1
9. Large scale drying of sugar is done in a __________ dryer.
Correct : C. Rotary
10. Though, theoretically the adsorption & desorption isotherms is expected to coincide but sometimes at least a part of the isotherms does not coincide and this phenomenon is known as adsorption hysteresis. In such cases, the desorption equilibrium pressure is __________ that obtained for adsorption.
Correct : A. Lower than
11. 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 metres) corresponding to an operating line given by, y = 5x + 0.001 is
Correct : A. 2.0
12. Reboiler is considered as one theoretical plate, because
Correct : A. Of the assumption that vapour and liquid leaving the reboiler are in equilibrium
13. In an absorption column, the flooding velocity for random packing is __________ that for stacked/regular packing.
Correct : B. Smaller than
14. 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:
Correct : B. 8.5 × 10-4
15. In case of cooling towers, the ratio of the rates of heat and mass transfer is indicated by the __________ number.
Correct : A. Lewis
16. When the gas to be dissolved in liquid is a/an __________ then normally co-current adsorber are used.
Correct : B. Pure gas
17. Unsaturated air (with dry and wet bulb temperatures being 35 and 25°C respectively) is passed through water spray chamber maintained at 35°C. The air will be
Correct : B. Humidified
18. __________ equation applies to diffusivities in liquids.
Correct : A. Gilliland
19. Mass transfer co-efficient is defined as
Correct : B. Co-efficient = Flux/concentration difference
20. The relative volatility of a binary mixture at constant temperature __________ the total pressure.
Correct : A. Decreases with increase in
21. Large quantity of silica gel is normally dried in a __________ dryer.
Correct : B. Through circulation
22. 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
Correct : D. Dependent on the Reynolds number
23. The value of „L/mG’ ratio for economical absorption operation ranges from
Correct : C. 1.25 to 2.0
24. 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).
Correct : A. log P vs. T
25. In a single stage extraction process, 10 kg of pure solvent S (containing no solute A) is mixed with 30 kg of feed F containing A at a mass fraction xf = 0.2. The mixture splits into an extract phase E and a raffinate phase R containing A at xB = 0.5 and xR = 0.05 respectively. The total mass of the extract phase is (in Kg)
Correct : B. 8.89
26. The commonly used solvent in supercritical extraction is
Correct : D. Carbon dioxide
27. Dried finished product sampled from various parts of a __________ dryer exhibits nonuniformity in the moisture content.
Correct : B. Tray
28. For the same system, if the same liquid used in an absorber is decreased, the tower height will
Correct : A. Increase
29. In steam distillation, the
Correct : C. Product must be immiscible with water
30. The equation, NA = (DAB . Pt /RTZ . PBM) (PA1 - PA2) is for
Correct : B. Steady state diffusion for stagnant case
31. A slurry is to be dried to produce flaky solid. Which dryer would you recommend?
Correct : A. Spray dryer
32. Perforated plate towers are unique for solvent extraction because, they provide
Correct : C. Repeated coalescence & redispersion of the drop phase
33. Which of the following parameters remains constant during chemical dehumidification?
Correct : A. Dry bulb temperature
34. 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)
Correct : A. G/(FG . a)
35. Coffee is prepared from coffee beans by leaching with
Correct : B. Hot water
36. Pore size of the molecular sieve 5A is __________ mm.
Correct : B. 0.5
37. The equation, NA = (DAB . Pt /RTZ) (y1 - y2) is for
Correct : A. Steady state equimolar counter diffusion
38. To remove all the moisture from a wet solid it requires exposure to __________ air.
Correct : A. Perfectly dry
39. Penetration theory states that the mass transfer co-coefficient is equal to (where, De is diffusivity and 't' is time)
Correct : C. (4De/πt)1/2
40. The cooling effect in a cooling tower can be speeded up by
Correct : D. All (A), (B) and (C)
41. The relative volatility of a binary mixture at the Azeotropic composition is
Correct : A. 1
42. Which of the following processes is not an example of adsorption applied to gaseous separations?
Correct : D. Decolouration of yellow glycerine
43. For absorbing a sparingly soluble gas in a liquid, the
Correct : B. Liquid side coefficient should be increased
44. The Knudsen diffusivity is proportional to (where, T = absolute temperature)
Correct : A. √T
45. Moisture content of a substance when at equilibrium with a given partial pressure of the vapour is called the __________ moisture.
Correct : C. Equilibrium
46. For the flow of gases through a capillary, with increase in temperature, the permeability
__________ as per Knudsen law.
Correct : A. Increases
47. A natural draft cooling tower is filled with wooden grids, which covers about __________
percent of the tower height.
Correct : A. 10-15
48. 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
Correct : C. Increases
49. Which of the following is not fixed by the process requirements, in the design of absorbers?
Correct : D. None of these
50. Pick out the wrong statement:
Correct : B. In case of a stripper, the equilibrium curve is always below the operating line
51. Which of the following processes is followed by unsaturated air (with dry bulb temperature 12°C and relative humidity 47%) passing through water spray washer (temperature of water being constant at 40°C?
Correct : C. Both heating and humidification
52. The velocity, concentration and temperature boundary, for the boundary layer development
on a flat plate during connective mass transfer will be same, if
Correct : B. NSc = NPr = NLe
53. Pick out the wrong statement. Generally for physical adsorption, a gas of
Correct : D. None of these
54. Co-current absorbers are usually used when the gas to be dissolved in the liquid is
Correct : C. A pure substance
55. Molecular sieves are regenerated by heating to __________ °C.
Correct : B. 200-330
56. In triangular co-ordinates, the ternary composition point falls __________ of the triangle.
Correct : B. Inside
57. When acetone is added in a two layer mixture of methyl isobutyl ketone and water at 30°C, the acetone distributes between the two layers and the composition of the layer follows two solubility curves. For this system,
Correct : D. All (A), (B) and (C)
58. During sensible cooling process
Correct : D. Both (B) and (C)
59. For stripping of a gas in a counter current stripper, the operating line
Correct : C. Can lie above or below the equilibrium curve
60. The Reynolds number of the liquid was increased 100 fold for a laminar falling film used for gas-liquid contacting. Assuming penetrating theory is applicable, the fold increase in the mass transfer co-efficient (Kc) for the same system is.
Correct : B. 10
61. The boiling points of pure components of a binary system __________ with increase in total pressure of the system.
Correct : B. Increases
62. In gas-liquid contact operation, the number of ideal stages, N = (xa - xb)/(xb - x*b). This is true when the stripping factor 'S' is
Correct : A. S > 1
63. Large scale usage of flash distillation is practised in
Correct : D. Petroleum refining
64. Drying of a solid involves __________ transfer.
Correct : C. Both heat and mass
65. Desulphurisation of petrol is done in a
Correct : B. Rotating disc extractor
66. Pick out the wrong statement
Correct : D. In actual practice, absorption is an endothermic process, while stripping is an exothermic process
67. Which of the following increases during evaporative cooling process with recirculated water supply?
Correct : D. Both (B) and (C)
68. Operating velocity in a packed tower is usually __________ the flooding velocity.
Correct : A. Half
69. For gas absorption, low viscosity solvents are preferred, because of their
Correct : D. All (A), (B) and (C)
70. Which of the following is used for the concentration of rubber latex?
Correct : A. Agitated film evaporator
71. Pressure drop through plate tower as compared to that through packed tower, for the same duty will be
Correct : B. More
72. In case of absorption & stripping, the interface of the liquid & gas phases are present in equilibrium, when the diffusional resistance of __________ is zero.
Correct : A. Interface
73. Henry's law states that the
Correct : A. Partial pressure of a component over a solution is proportional to its mole fraction in the liquid
74. The change in enthalpy, when a unit quantity of gas is absorbed by relatively large quantity of adsorbent (on which a definite concentration of the adsorbed gas already exists) is termed as the
Correct : A. Differential heat of adsorption
75. A 25 cm × 25 cm × 1 cm flat sheet weighing 1.2 kg initially was dried from both sides under constant drying rate conditions. It took 1500 seconds for the weight of the sheet to reduce to 1.05 kg. Another 1m × 1m × 1cm flat sheet of the same material is to be dried from one side only. Under the same constant drying rate conditions, the time required for drying (in seconds) from its initial weight of 19.2 kg to 17.6 kg is
Correct : A. 1000
76. Moisture in a solid exerting an equilibrium vapour pressure equal to that of the pure liquid at the same temperature is called the __________ moisture.
Correct : A. Unbound
77. Swenson-Walker crystalliser is a __________ unit.
Correct : A. Continuous
78. For a binary mixture distillation process, the degree of freedom is 2. However, if the pressure is fixed in this process, the number of independent variables in this process will be
Correct : A. 1
79. Calculation of mass transfer co-efficient is mostly/normally done using __________ theory.
Correct : B. Film
80. With increase in temperature, the leaching rate increases because of the
Correct : C. Both (A) and (B)
81. Relative volatility varies with the concentration of component for an ideal solution. The relative volatility of a binary mixture may be defined as the ratio of vapor pressure of component 'A' to that of component 'B', when
Correct : D. Vapor phase obeys Dalton's law and liquid phase obeys Raoult's law
82. Which one of the following devices is not used for both the absorption as well as the liquidliquid extraction processes?
Correct : D. Wetted wall columns
83. Penetration theory relates the average mass transfer co-efficient (K) with diffusivity (D) as
Correct : B. K ∝√D
84. Pick out the wrong statement.
Correct : C. When Henry's law constant is very small, then the mass transfer rate is controlled by the gas film resistance
85. For water-ethanol system, the minimum reflux ratio
Correct : A. Is computed from the slope of the upper operating line that is tangent to the equilibrium curve
86. 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?
Correct : D. Selectivity
87. At 750°K and 1 atm, the approximate value of Schmidt number for air is
Correct : B. 0.1
88. What is the degree of freedom of an absorption process in which only one component is transferred between phases?
Correct : C. 3
89. Rayleigh equation applies to __________ distillation.
Correct : A. Differential
90. In a vapor-liquid contacting equipment, the overall gas phase mass transfer co-efficient (M.T.C), KG is related to individual co-efficients (KG and KL) as
Correct : B. 1/KG = 1/KG + m/KL
91. Leaching of coarse solid lumps is also termed as
Correct : C. Percolation
92. Which of the following can be calculated theoretically using steam table and Dalton's law of partial pressure; if the relative humidity and dry bulb temperature of moist air is known?
Correct : C. Wet bulb temperature
93. Danckwerts developed the __________ theory.
Correct : B. Surface renewal
94. Steam distillation is used to
Correct : B. Avoid thermal decomposition of a component
95. When an unsaturated air-water mixture is heated at constant pressure, then
Correct : D. The relative humidity decreases
96. Flash distillation is
Correct : B. Used for multi-component systems like crude refining
97. Mechanism of moisture removal in case of freeze drying of food stuff is by
Correct : B. Sublimation
98. Molality is defined as the number of gm moles of solute per __________ of solvent.
Correct : C. Kg
99. When the mixture to be distilled has a very high boiling point and the product material is heat sensitive, the separation technique to be used is __________ distillation.
Correct : B. Steam
100. Alcohol is dehydrated using __________ distillation.