Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemical Engineering Reviewer > Mass Transfer (Set 6) > Flashcards

Mass Transfer (Set 6) 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

In a binary system, separation is very efficient, when the relative volatility is

A

> 1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Fenske-Underwood equation used for calculating the minimum number of theoretical plates in distillation column is valid for

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

The binary diffusivity in gases does not depend upon the

A

none of these

Not pressure, temperature, and nature of components

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Berl saddle made of carbon cannot be used for

A

oxidising atmosphere

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

1 kg of a saturated aqueous solution of a highly soluble component A at 60°C is cooled to 25°C. The solubility limits of A are (0.6 kgA/kg water) at 60°C and (0.2 kgA/kg water) at 25°C. The amount in kg of the crystals formed is

A

0.2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

During drying of a solid, the critical moisture content increases with
a. decreased drying rate
b. increased thickness of the solid
c. increased drying rate
d. both (b) and (c).

A

both (b) and (c).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Priming in a distillation column

A

is characterised by the presence of foam throughout the space between trays.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

The commonly used solvent in supercritical extraction is

A

carbon dioxide.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When the liquid over a plate is of uniform concentration, then

A

Murphree efficiency = point efficiency.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

In saturated gas, the

A

vapour is in equilibrium with the liquid at the gas temperature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

As per Gilliland’s equation, the diffusivity is

A

all ‘a’, ‘b’ & ‘c’.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Pick out the wrong statement.

A

The operating line lies above the equilibrium curve in case of a gas desorber.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

A mixture of 10% C6H6 vapour in air at 25°C and 750 mm Hg has a dew point of 20°C. Its dew point at 30°C and 700 mm Hg will be around ____ °C.

A

18.7

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Which of the following is not fixed by the process requirements, in the design of absorbers?

A

None of these.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

If the amount of the steam used in steam distillation is increased, the temperature of distillation

A

decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Moisture in a solid exerting an equilibrium vapour pressure equal to that of the pure liquid at the same temperature is called the ____ moisture.

A

unbound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Inside the distillation columns, the

A

driving force for the liquid flow is its weight.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

When the psychometric ratio is ____ then the adiabatic saturation temperature and wet bulb temperature becomes equal.

A

1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Desirable value of absorption factor in an absorber is

A

> 1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Refractory bricks are usually dried in a ____ dryer.

A

tunnel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

For ____ drying, the effects of velocity, temperature and humidity of the gas and the thickness of the solid are the same.

A

both (a) and (b)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the degree of freedom of an absorption process in which only one component is transferred between phases?

A

3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Sticky material can be dried in a ____ dryer.

A

tray

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Langmuir equation is associated with

A

adsorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

During the constant rate period of drying of a solid,

A

surface evaporation of unbound moisture occurs.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

At a fixed total pressure, humidity depends only on the

A

partial pressure of vapour in the mixture.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

If moisture content of solid on dry basis is X, then the same on wet basis is

A

X/X+1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Flash distillation is

A

used for multicomponent systems like crude refining.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

____ developed the film theory.

A

Higbie

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

For absorbers, high pressure drop results in

A

high operating cost.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Which of the following parameters remains almost constant during adiabatic saturation of unsaturated air?

A

Wet bulb temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Coffee is prepared from coffee beans by leaching with

A

hot water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Gaseous diffusion co-efficient increases with increase in the

A

temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

With increase in absolute humidity, the dew point of an unsaturated mixture of air and water vapor (at constant pressure and temperature)

A

increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

If xD = overhead product molal composition and RD = reflux ratio, then slope and intercept of the operating line for rectifying section are respectively

A

https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/287-102-2.png

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Pick out the wrong statement. Raoult’s law does not apply, when the

A

component molecules are nonpolar.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Water-ethyl alcohal solution can be concentrated (in respect of alcohal concentration) by ____ distillation.

A

vacuum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

L/mG is the expression for

A

absorption factor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Extraction of pencillin employs a ____ extraction coloumn.

A

centrifugal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

In case of gases, the binary diffusivity is proportional to (where, P = pressure)

A

1/P

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

When the gas to be dissolved in liquid is a/an ____ then normally co-current adsorber are used.

A

pure gas

42
Q

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

A

Schmidt

43
Q

If a two phase system is in physical equilibrium; then it means that, the

A

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

44
Q

McCabe-Thiele method of binary distillation does not assume that the

A

none of these

45
Q

(NSh/NRe.NSc) is termed in mass transfer operation as the

A

Stanton number

46
Q

The Hatta number is important in

A

gas absorption with chemical reaction.

47
Q

When a multistage tray tower uses a minimum reflux ratio, it implies

A

infinite trays and minimum reboiler heat load.

48
Q

CO2 can be absorbed by

A

heated charcoal

49
Q

For the same process conditions, the reflux ratio of an unlagged distillation column

A

increases in winter

50
Q

An ideal tower packing should not

A

hold up large amount of liquid in the packing.

51
Q

Which of the following is a suitable absorbent for removal of H2S from natural gas?

A

Monoethanol amine (MEA)

52
Q

Acetone is to be removed from air in an isothermal dilute absorber using pure water as solvent. The incoming air contains 5 mole% of acetone (yin = 0.05). The design equation to be used for obtaining the number of trays (N) of the absorber is, N+2 = 6 log (yin/yout).For 98% recovery of acetone, the number of trays required is/are

A

9

53
Q

Schimdt number and Lewis number for pure air at atmospheric conditions are respectively

A

< 1 and ≈ 1

54
Q

Below is given an equilibrium moisture curve of a substance. State which regions represent free moisture and unbound moisture respectively. https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/292-170-1.png

A

II, III

55
Q

Molecular diffusion is caused by the

A

thermal energy of the molecules.

56
Q

At ____ reflux, theoretical number of plates in a distillation coloumn is calculated using Fenske-Underwood equation.

A

total

57
Q

Separation of a mixture of two gases by absorption in the liquid solvent depends upon the difference in their

A

solubility

58
Q

Components, having widely different boiling point in a binary mixture, can be separated using ____ distillation.

A

simple

59
Q

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

A

Pachuka tank

60
Q

Pick out the wrong statement.

A

Diameter of randomly packed tower is normally more than 1.2 metres.

61
Q

Equilibrium-moisture curves of different solids

A

are different

62
Q

Azeotropism for ethyl alcohol-water system disappears by

A

decreasing pressure

63
Q

Degree of freedom for leaching and solvent extraction process is

A

3

64
Q

Diffusion co-efficient generally depends upon the temperature, pressure & the nature of the components of the system. Its dimension is not the same as that of the

A

mass transfer co-efficient.

65
Q

Equilibrium moisture of a solid is equal to the total moisture minus free moisture. Which of the following substances will have maxi-mum equilibrium moisture?

A

Bamboo

66
Q

In the absorption of ammonia in water, the main resistance to absorption is by the ____ phase.

A

gas

67
Q

Drying of refractory is normally carried out in a ____ dryer.

A

truck/tunnel.

68
Q

The expression, ln(F/W) = https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/314-454-1.png is

A

differential distillation equation

69
Q

Heat sensitive materials with very high latent heat of vaporisation may be economically separated using

A

liquid extraction

70
Q

When the solvent dissolves very little of solute, then

A

large quantity of solvent is required to extract the solute.

71
Q

An alkaline solution is used to reduce the concentration of carbon dioxide in a stream from 10% to 0.1% by absorption with irreversible chemical reaction. The overall number of transfer units based on gas phase is

A

4.605

72
Q

HETP is numerically equal to HTU, only when the operating line

A

and equilibrium lines are parallel.

73
Q

In a distillation operation, what is the effect of the temperature of the reflux stream (given below) on the condenser and reboiler loads ?
Reflux conditions:
(i) Reflux stream is completely liquid and is at its bubble point.
(ii) Reflux stream is below its bubble point.

A

Both condensor and reboiler loads are higher in case (ii) as compared to case (i).

74
Q

Steady state equimolal counter diffusion occurs in case of

A

binary phase distillation

75
Q

JD factor for mass transfer is a function of Reynolds number. Mass transfer by molecular diffusion from a single drop to surrounding still air is given by

A

Nsh = 2

76
Q

The relative saturation of an unsaturated mixture of gas and vapor is independent of the

A

none of these.

77
Q

The adiabatic saturation curve for a vapour-gas mixture is

A

slightly concave upward.

78
Q

Pick out the wrong statement.

A

Zirconia probe is used for the humidity measurement.

79
Q

The value of NA/(NA + NB), for steady state equimolal counter diffusion of two gases ‘A’ and ‘B’ is

A

∞

80
Q

Drift in a cooling tower is

A

the water entrained by the circulating air.

81
Q

With increase in the concentration of the adsorbate, the integral heat of adsorption

A

decreases.

82
Q

Small dia distillation column can be a

A

packed column

83
Q

If mass diffusivity in a mixture is equal to the thermal diffusivity, then the Lewis number is

A

1

84
Q

An air-water vapour mixture has a dry bulb temperature of 60°C and a dew point temperature of 40°C. The total pressure is 101.3 kPa and the vapour pressure of water at 40°C and 60°C are 7.30 kPa and 19.91 kPa respectively.The humidity of air sample expressed as kg of water vapour/kg of dry air is

A

0.152

85
Q

____ column is used in gas absorption process.

A

Packed

86
Q

Nitrobenzene (boiling point = 210.6°C) is steam distilled at 1 atm pressure.Nitrobenzene will distill off ____ °C.

A

at < 100

87
Q

Pick out the wrong statement.

A

Vanderwall adsorption is also called chemisorption.

88
Q

At what value of reflux ratio, number of theoretical plates in a distillation column is minimum?

A

∞

89
Q

Batch tray dryers suffers from the disadvantage of

A

high labour cost & low heat economy.

90
Q

In a moderately sized packed absorption tower, channeling (which is most severe with stacked packings) can be minimised by taking the ratio of tower diameter to packing diameter

A

> 8:1

91
Q

____ column is preferred to be used, when a high liquid hold up is required in a reactor for gas-liquid reaction.

A

Bubble

92
Q

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

A

both (a) and (b).

93
Q

Penetration model (theory) for mass transfer was enunciated by

A

Higbie

94
Q

Surface renewal model of mass transfer was enunciated by

A

Danckwerts

95
Q

When the ____ the relative humidity of air decreases, despite an increase in the absolute humidity.

A

temperature rises

96
Q

For turbulent mass transfer in pipes, the Sherwood number depends on the Reynolds number as

A

Re^0.83

97
Q

The relative humidity of air decreases in-spite of an increase in the absolute humidity, when the

A

temperature rises.

98
Q

Unit of molal diffusivity is

A

gm moles/cm. sec

99
Q

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

A

cold water leaving the tower and the wet bulb temperature of the surrounding air.

100
Q

Binary distillation involves the mass transfer by ____ at the gas-liquid interface.

A

a counter diffusion at an almost equal molar rate

Chemical Engineering Reviewer (44 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions