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Chemical Engineering Reviewer > Mass Transfer (Set 1) > Flashcards

Mass Transfer (Set 1) Flashcards

As one of the transport phenomena, the concepts in mass transfer are crucial for design, operation, and maintenance of mass or heat & mass transfer equipment such as mixing and separation processes.

1
Q

Mass transfer rate between two fluid phases does not necessarily depend on the ____ of the two phases.

A

chemical properties

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2
Q

In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the molality is

A

0.5

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3
Q

Fenske equation determines the

A

minimum number of theoretical plates.

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4
Q

The term “cooling range” in a cooling tower refers to the difference in the temperature of

A

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

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5
Q

Which of the following is the most suitable for extraction in a system having very low density difference?

A

Centrifugal extractor

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6
Q

Total reflux in a distillation operation requires minimum

A

number of plates

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7
Q

The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by

A

both (a) and (b).

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8
Q

The difference of wet bulb temperature and adiabatic saturation temperature of unsaturated mixture of any system is

A

(+)ve

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9
Q

Fenske’s equation for determining the minimum number of theoretical stages in distillation column holds good, when the

A

relative volatility is reasonably constant.

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10
Q

When the temperature and humidity of air is low, we usually use ____ draft cooling tower.

A

natural

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11
Q

Pick out the correct statement.

A

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

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12
Q

____ columns are used for liquid dispersion in a continuous gas phase.

A

Packed

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13
Q

Overall efficiency of the distillation column is

A

the ratio of number of ideal plates to actual plates.

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14
Q

On addition of solute in the solvent, the ____ of the solution decreases.

A

both (b) and (c)

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15
Q

Which is the controlling factor for a drum drier?

A

Heat transfer

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16
Q

Drying operation under vacuum is carried out to

A

reduce drying temperature.

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17
Q

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 relative humidity

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18
Q

Separation of two or more components of a liquid solution can not be achieved by

A

absorption

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19
Q

Stefan’s law describes the mass transfer by

A

both ‘a’ & ‘b’

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20
Q

At minimum reflux ratio for a given separation

A

number of plates is infinity.

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21
Q

Relative humidity is the ratio of the

A

partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.

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22
Q

In batch distillation with constant reflux, overhead product composition ____ with time.

A

decreases

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23
Q

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

A

electrical resistance

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24
Q

Heat in BTU necessary to increase the temperature of 1 lb of gas and its accompanying vapour by 1°F is called the

A

specific heat

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25
Q

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

A

increase ‘S’ and decrease ‘G’.

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26
Q

The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are same for, NPr = NSc = ____

A

1

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27
Q

Dew point of a gas-vapour mixture

A

decreases with decrease in pressure.

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28
Q

In a packed absorption tower, if the equilibrium and operating lines are both straight lines, then the ratio, HETP/HTUOG ____ the absorption factor.

A

both (a) and (b)

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29
Q

Which of the following plays an important role in problems of simultaneous heat and mass transfer?

A

Lewis number

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30
Q

In case of an absorber, the operating

A

line always lies above the equilibrium curve.

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31
Q

As the reflux ratio in a distillation coloumn is increased from the minimum, the

A

total cost first decreases and then increases.

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32
Q

Absorption factor is defined as (where, S1 = slope of the operating line S2 = slope of the equilibrium curve)

A

S1/S2

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33
Q

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

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34
Q

Which of the following remains constant during sensible cooling process?

A

Both (a) and (b)

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35
Q

Physical absorption is

A

both (b) and (c)

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36
Q

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

A

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

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37
Q

Which of the following quantities need not be fixed before starting the design of a co-current absorber?

A

Flow rate of entering liquid

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38
Q

Mass transfer co-efficient of liquid is

A

affected more by temperature than that for gases.

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39
Q

Absorption accompanied with chemical reaction is exemplified by the absorption of

A

SO2 in alkaline solution.

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40
Q

Which of the following unit operations makes use of Thiele-Geddes equation?

A

Multicomponent distillation.

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41
Q

Which of the following liquid-vapor contacting devices provides maximum contact surface area for a particular duty?

A

Wetted wall column

42
Q

The equipment frequently used for adiabatic humidification-cooling operation with recirculating liquid is

A

spray chamber

43
Q

Chemisorption (chemical adsorption) is

A

an irreversible phenomenon.

44
Q

The rate of solid-liquid extraction is limited by the

A

all ‘a’, ‘b’ & ‘c’.

45
Q

Raoult’s law applies to the

A

solvents.

46
Q

In distillation columns, the number of bubble caps per tray primarily depends upon the

A

allowable gas and liquid velocities.

47
Q

In distillation, overhead product contains

A

any number of components

48
Q

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

A

decreases.

49
Q

Low viscosity absorbent is preferred for reasons of

A

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

50
Q

Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as

A

K ∝ D

51
Q

The McCabe Δ L law states that the

A

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

52
Q

Bollman extractor

A

is used for extraction of oil from oilseed.

53
Q

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

A

heat and mass

54
Q

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

A

all ‘a’, ‘b’, & ‘c’.

55
Q

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

56
Q

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.

57
Q

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.

58
Q

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

elutriation or elution

59
Q

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

A

surface evaporation of unbound moisture occurs.

60
Q

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

71 min

61
Q

Agitator is provided in a crystalliser for

A

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

62
Q

____ diffusion is used for separating the isotopes of methane.

A

Thermal

63
Q

Ordinary diffusion process is also called ____ diffusion.

A

concentration

64
Q

Pick out the wrong statement.

A

Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column.

65
Q

Pick out the wrong statement pertaining to the rotary dryer.

A

Rotary dryer is suitable for drying sticky material.

66
Q

The reason for preferring packed towers over plate towers in distillation practice is that the packed tower operation gives

A

low pressure drop and low hold up.

67
Q

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

68
Q

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

0.5

69
Q

Raoult’s law is applicable to the

A

ideal solutions

70
Q

Weeping in a distillation column

A

results due to very low gas velocity.

71
Q

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.

72
Q

Wetted wall tower experiment determines the

A

mass transfer co-efficient.

73
Q

In McCabe-Thiele method, at infinite reflux ratio

A

the overhead product is minimum.

74
Q

With decrease in the throughput (compared with the design capacity) for a bubble cap distillation column, its efficiency

A

increases

75
Q

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.

76
Q

The equilibrium liquid composition compared to the vapor composition in case of azeotropic mixture is

A

same

77
Q

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

78
Q

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

A

ethyl alcohol-water

79
Q

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

A

rotary

80
Q

In case of an ideal solution, the total vapor pressure varies ____ with the composition expressed as mole fraction,

A

linearly

81
Q

Corresponding to Nusselt number in heat transfer, the dimensionless group in mass transfer is the ____ number.

A

Sherwood

82
Q

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

0.215

83
Q

Liquid diffusivity is of the order of ____ cm2 /second.

A

10-5 to 10-6

84
Q

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

A

its recovery cost by distillation may be prohibitatively high.

85
Q

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

86
Q

Molarity is defined as the number of gm moles of solute per ____ of solvent.

A

liter

87
Q

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

A

1

88
Q

Which of the following T-H diagram is valid for dehumidification operation?

A

https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/317-501-1.png

89
Q

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.

90
Q

The partial pressure distribution of an ideal gas diffusing through another stagnant ideal gas at steady state follows a/an ____ law.

A

exponential

91
Q

Which of the following binary systems is an example of a maximum boiling azeotrope?

A

Water-hydrochloric acid.

92
Q

(NRe . NSc) is termed in mass transfer operation as the ____ number.

A

Peclet

93
Q

The binary diffusivity in gases and liquids vary respectively as

A

T^3/2 and T

94
Q

Pick out the correct statement.

A

In Ponchon-Savarit method of no. of theoretical plate determination, the stripping and rectifying operating lines are vertical at total reflux.

95
Q

Pick out the correct statement.

A

Electrodylsis is used in the manufacture of NaOH.

96
Q

Pick out the correct statement.

A

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

97
Q

Very tall packed towers are divided into series of beds to

A

avoid channelling

98
Q

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

A

free

99
Q

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

A

decreases

100
Q

In most of the vacuum crystalliser, vacuum is generally produced by means of a

A

steam jet ejector with a barometric condenser

Chemical Engineering Reviewer (44 decks)

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