IndiaBIX Chemical Engineering: Mass Transfer Section 9 Flashcards

1
Q

Which of the following parameters remains constant during chemical dehumidifica-tion?

Dry bulb temperature

Partial pressure of vapour

Wet bulb temperature

None of these

A

Dry bulb temperature

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2
Q

Drying of a solid involves __________ transfer.

only heat

only mass

both heat and mass

none of these

A

both heat and mass

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3
Q

Mechanism of moisture removal in case of freeze drying of food stuff is by

evaporation

sublimation

dehydration

adsorption

A

sublimation

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4
Q

The dew point of an unsaturated gas-vapor mixture does not depend upon the __________ of the mixture.

composition

temperature

total pressure

all (a),

(b) and (c)

A

temperature

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5
Q

Which is not concerned directly with mass transfer ?

Schmidt number

Sherwood number

Lewis relationship

Froude number

A

Froude number

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6
Q

Removal of __________ exemplifies an adsorption unit operation.

uranium from its ore

water from petrol

ammonia from coke oven gas

mustard oil from mustard seed

A

water from petrol

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7
Q

Can the efficiency of a plate in the distillation tower be greater than 100% ?

Yes

Normally not; but is possible if infinite number of plates are put.

Never

Yes ; if the reflux ratio is maximum.

A

Never

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8
Q

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.

increases

decreases

remains same

increases linearly

A

increases

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9
Q

For gas absorption,

low viscosity solvents are preferred,

because of their

better flow characteristics.

low pumping pressure drop.

rapid absorption rates.

all (a),

(b) and (c).

A

all (a),

(b) and (c).

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10
Q

To remove all the moisture from a wet solid it requires exposure to __________ air.

perfectly dry

highly humid

high temperature

none of these

A

perfectly dry

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11
Q

The operating cost of a distillation column at minimum reflux ratio is

minimum

maximum

infinite

zero

A

minimum

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12
Q

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

A

2

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13
Q

Molecular diffusivity of a liquid

increases with temperature.

decreases with temperature.

may increase or decrease with temperature.

is independent of temperature.

A

increases with temperature.

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14
Q

The wet and ‘dry bulb temperature for a vapour-gas mixture are 25°C and 30°C respectively. If the mixture is heated to 45°C at constant pressure,

the wet bulb temperature will be __________ °C.

25

> 25

< 25

  • 25
A

> 25

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15
Q

Henry’s law states that the

partial pressure of a component over a solution is proportional to its mole fraction in the liquid.

partial pressure of a component over a solution is proportional to the mole fraction in the vapour.

vapour pressure is equal to the product of the mole fraction and total pressure.

partial pressure is equal to the product of the mole fraction and total pressure.

A

partial pressure of a component over a solution is proportional to its mole fraction in the liquid.

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16
Q

Ammonia present in the coke oven gas is removed by washing with

caustic solution

dilute ammoniacal liquor

dilute HCl

ethanolamine

A

dilute ammoniacal liquor

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17
Q

With increase in temperature,

the leaching rate increases due to

decreased liquid viscosity

increased diffusivity

both (a) and (b)

neither (a) nor (b)

A

both (a) and (b)

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18
Q

Which of the following processes is not an example of adsorption applied to gaseous separations ?

Recovery of valuable solvent vapors from dilute mixture with air and other gases.

Dehumidification of air and gas.

Removal of objectionable odour and impurities from industrial gases.

Decolouration of yellow glycerene.

A

Decolouration of yellow glycerene.

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19
Q

The critical moisture content in case of drying indicates the __________ rate period.

beginning of falling

beginning of constant

end of falling

none of these

A

beginning of falling

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20
Q

Pick out the wrong statement

A horizontal line on the humidity chart indicates the temperature changes at constant molal humidity.

When water is cooled from 80 to 70°C by exposure to the air with a wet bulb temperature of 60°C,

then both the approach & the range would be 10°C.

For unsaturated air-water vapor mixture at atmospheric conditions,

the wet bulb temperature & adiabatic cooling lines are the same.

Relative saturation of unsaturated mixture of water vapor & air can not be increased by either reducing the mixture temperature or by increasing the total pressure.

A

Relative saturation of unsaturated mixture of water vapor & air can not be increased by either reducing the mixture temperature or by increasing the total pressure.

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21
Q

According to Poiseuille’s law,

the permeability for gas flow through a capillary is proportional to (where,

μ = gas viscosity)

μ

1/μ

sqrt(μ)

μ^2

A

1/μ

22
Q

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

1

0

2

3

A

1

23
Q

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

2.0

1.56

1.0

0.56

A

2

24
Q

Packed column distillation is limited to the column __________ metres.

height < 6

diameter < 0.6

both (a) & (b)

neither (a) nor (b).

A

both (a) & (b)

25
Q

For the flow of gases through a capillary,

with increase in temperature,

the permeability __________ as per Knudsen law.

increases

decreases

remains same

either (a) or (b); depends on the gas

A

increases

26
Q

Which of the following is directly concerned with psychrometry ?

Lewis reltionship

Galileo number

Weber number

Dean number

A

Lewis reltionship

27
Q

Plate efficiency in a distillation column is reduced due to the __________ of liquid.

entrainment

foaming

weeping & dumping

all (a),

(b) & (c)

A

all (a),

(b) & (c)

28
Q

The most efficient cooling tower out of the following is

induced draft

forced draft

natural draft

atmospheric

A

induced draft

29
Q

Sodium bicarbonate is produced during soda ash manufacture using a __________ tower.

plate

baffle

packed

none of these

A

baffle

30
Q

Powdery materials can be guarded against caking tendency on storage by

providing irregular grain size.

providing minimum percentage of voids.

having maximum possible points of contact.

none of these.

A

none of these.

31
Q

In case of cooling towers,

the ratio of the rates of heat and mass transfer is indicated by the __________ number.

Lewis

Grashoff

Sherwood

none of these

A

Lewis

32
Q

Which one of the following devices is not used for both the absorption as well as the liquid-liquid extraction processes ?

Packed towers

Plate towers

Spray towers

Wetted wall columns

A

Wetted wall columns

33
Q

The temperature of water cooled in cooling tower is always __________ temperature of entering air.

more than the wet bulb

less than the wet bulb

equal to the wet bulb

equal to the dry bulb

A

more than the wet bulb

34
Q

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?

Humidification only

Heating only

Both heating and humidification

Evaporative cooling

A

Both heating and humidification

35
Q

Mass transfer co-efficient is directly proportional to DAB according to the __________ theory.

film

penetration

surface-renewal

none of these

A

film

36
Q

The relative volatility of a binary mixture at constant temperature __________ the total pressure.

decreases with increase in

increases with increase in

is independent of

none of these

A

decreases with increase in

37
Q

Tower diameter may be decreased by

using higher reflux ratio.

use of increased tray spacing.

increasing the liquid flow rate.

increasing the vapour flow rate.

A

use of increased tray spacing.

38
Q

Rayleigh’s equation applies to __________ distillation.

continuous

steam

differential

flash

A

differential

39
Q

Steady state equimolal counter diffusion is encountered in

separation of a binary mixture by distillation.

absorption of NH3 from air by water.

all liquid-liquid diffusion systems.

all liquid-solid diffusion systems.

A

separation of a binary mixture by distillation.

40
Q

Which of the following is considered equivalent to one theoretical stage in Mc-Cabe Thiele’s method ?

Partial condenser

Total condenser

Reboiler

Both (b) and (c)

A

Both (b) and (c)

41
Q

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

A

Selectivity

42
Q

As the reflux ratio increases,

the slope of the operating line for rectifying section

increases

decreases

remains constant

data insufficient,

cannot be predicted

A

increases

43
Q

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)

log P vs . T

log P vs. log T

T vs. P

P vs . log T

A

0

44
Q

The unit of volumetric diffusivity is

cm2/sec

cm/sec

cm3/sec

cm2/sec2

A

cm

45
Q

For a ternery mixture,

in which equilateral triangular co-ordinate is used in leaching and extraction,

a __________ of the equilateral triangular co-ordinates.

binary mixture is represented by the apex

binary mixture is represented by any point inside

ternery mixture is represented by the sides

pure component is represented by the apex.

A

pure component is represented by the apex.

46
Q

Steady state temperature reached by a small amount of liquid evaporating into a large amount of unsaturated vapour-gas mixture is called the __________ temperature.

dry-bulb

wet-bulb

dew point

adiabatic saturation

A

wet-bulb

47
Q

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 sytem is

100

10

5

1

A

10

48
Q

The slope of 9-line is determined by the

reflux ratio

plate efficiency to be achieved

thermal condition of the feed

relative volatility.

A

thermal condition of the feed

49
Q

In steam distillation,

the

temperature is 100°C.

temperature is more than 100° C.

product must be immiscible with water.

temperature is higher than the boiling point of either component.

A

product must be immiscible with water.

50
Q

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 ?

Dew point

Humidity ratio

Wet bulb temperature

None of these

A

Wet bulb temperature