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ChELE 2024 > IBX- Mass Transfer 13-14 > Flashcards

IBX- Mass Transfer 13-14 Flashcards

1
Q

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.

A

both gas as well as liquid streams should be distributed uniformly.

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2
Q

Reverse osmosis is also called
dialysis
electrodilysis
diffusion
ultrafiltration.

A

ultrafiltration.

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3
Q

Which of the following is not a batch drier?
Truck drier
Agitated pan drier
Fluidised bed drier
Vacuum shelf drier

A

Fluidised bed drier

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4
Q

Steam distillation is not recommended to be used, if the

azeotropic mixture is to be separated and the final product is miscible with water.

liquids decompose, if distilled directly at atmospheric pressure.

material can not be distilled by indirect heating even under low pressure, because of the high boiling temperature.

material to be distilled is thermally unstable or has the tendency to react with other components associated with it, at the boiling temperature.

A

azeotropic mixture is to be separated and the final product is miscible with water.

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5
Q

Rayleigh equation applies to __________ distillation.
differential
flash
equilibrium
molecular

A

differential

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6
Q

Mass transfer co-efficient ‘K’ according to penetration theory varies with mass dif-fusivity as
D^0.5
D
1/D
D^1.5

A

D^0.5

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7
Q

Most important factor to be considered in the selection of packings for absorbers is the __________ of packing.
size
durability
porosity
cost

A

porosity

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8
Q

__________ is the separation technique used for desalination of sea water.
Thermal diffusion
Reverse osmosis
Adsorption
absorption

A

Reverse osmosis

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9
Q

The relative saturation of a partially saturated mixture of vapour and gas can be increased by __________ of the mixture.
reducing the total pressure
increasing the total pressure
reducing the temperature
both (b) and (c)

A

both (b) and (c)

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10
Q

Danckwerts developed the __________ theory.
penetration
surface renewal
film
none of these

A

surface renewal

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11
Q

Molecular distillation is
high temperature distillation
for heat-sensitive materials
very low pressure distillation
both (b) and (c)

A

both (b) and (c)

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12
Q

Drying of a wet solid under constant drying conditions means the exposure of the wet solid to the air of constant
humidity
velocity
temperature
all (a), (b) & (c)

A

all (a), (b) & (c)

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13
Q

Which of the following provides maximum contact surface for a liquid-vapour system?
Packed tower
Bubble-cap plate column
Seive-plate column
Wetted wall column

A

Packed tower

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14
Q

For experimental determination of mass transfer co-efficient by wetted wall tower, the mass transfer area is
calculated
unknown
known
not required

A

known

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15
Q

In stripping section of continuous distillation column, the
liquid is stripped of high boiler.
liquid is enriched with high boiler.
vapour is stripped of low boiler.
none of these.

A

liquid is enriched with high boiler.

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16
Q

Molality is defined as the number of gm moles of solute per __________ of solvent.
litre
gm
Kg
m3

A

Kg

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17
Q

__________ is concerned with the adsorption equilibria.
Fick’s law
Gibb’s equation
Freundlich equation
none of these

A

Freundlich equation

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18
Q

Figure

A

A

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19
Q

Fractional solvent extraction
employs only one solvent
employs two solvents
results in low interfacial tension
none of these solvents

A

employs two solvents

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20
Q

In the layout plan for a vacuum distillation unit, operating at 60 mm Hg, supported by a barometric condenser, the appropriate place for the location of vacuum drum for collecting the distillate will be
at ground level.
2 metres above the ground.
5 metres above ground.
10 metres above ground.

A

at ground level.

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21
Q

Raschig ring made of procelain cannot be used for treating concentrated
hydrochloric acid
nitric acid
alkalis
sulphuric acid

A

alkalis

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22
Q

H2S present in naphtha reformed gas is removed by absorbing with
ethanolamine
K2CO3
HCl
vacuum gas oil

A

ethanolamine

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23
Q

During constant rate drying period, vaporisation rate per unit drying surface area
decreases with time.
increases with time.
does not change with time,
does not affect the moisture content of the wet solid.

A

does not change with time,

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24
Q

Pick out the wrong statement.

Mass transfer co-efficient does not account for gase-liquid diffusion.

Diffusion co-efficient and mass transfer co-efficient are not same in any mass transfer operation.

Contacting cold vapor-gas mixture with hot liquid exemplifies humidification process.

Contacting cold liquid with warm vapor-gas mixture exemplifies dehumidification process.

A

Mass transfer co-efficient does not account for gase-liquid diffusion.

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25
Q

In rectifying section of a continuous distillation column, the
vapour is enriched with low boilers.
vapour is enriched with high boilers.
liquid is stripped of high boilers.
none of these.

A

vapour is enriched with high boilers.

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26
Q

For a fixed number of ideal stages in a distillation column, as the reflux ratio is increased, the difference in composition between the top and bottom product streams
increases
decreases
remains unaffected
passes through a maximum

A

increases

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27
Q

According to Chilton-Colburn analogy for mass transfer, NSt.NSc2/3 is equal to
f
f/2
2f
1/f

A

f/2

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28
Q

A pure drug is administered as a sphere and as a cube. The amount of drug is the same in the two tablets. Assuming that the shape and size do not influence the mass transfer, the ratio of rate of dissolution in water at t = 0 for the cubic to spherical tablet is

A

1.24

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29
Q

Minimum reflux ratio in a distillation column results in
optimum number of trays.
minimum reboiler size.
maximum condenser size.
minimum number of trays.

A

maximum condenser size.

30
Q

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.

A

increase in pressure drop.

31
Q

In extraction, as the temperature increases, the area of hetrogeneity (area covered by binodal curve)
decreases
increases
remains unchanged
none of these

A

decreases

32
Q

Pick out the wrong statement.

The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are the same for NSc = NPr = 1.

1 Nm3 of dry air is lighter than 1Nm3 of humid air.

The Lewis number of a mixture is unity, when the thermal diffusivity is equal to the mass diffusivity.

An azeotropic mixture of two liquids has boiling point higher than either of them, when it shows negative deviation from Raoult’s Law.

A

1 Nm3 of dry air is lighter than 1Nm3 of humid air.

33
Q

In case of an unsaturated mixture of gas and vapor, the percentage saturation is __________ its relative saturation.
lower than
higher than
equal to
either (a) or (b), depends on the mixture composition

A

lower than

34
Q

At constant pressure, with increase of temperature, the dew point will
increase
decrease
remain unchanged
increase/decrease ; depends on the temperature

A

increase

35
Q

For a single component absorber, the operating line is straight only when plotted in term of __________ units.
partial pressure
mole ratio
mole fraction
none of these

A

mole ratio

36
Q

In case of unsaturated air
dew point < wet bulb temperature
wet bulb temperature < dry bulb temperature
both (a) and (b)
neither (a) not (b)

A

both (a) and (b)

37
Q

For a binary mixture with low relative volatility,
use steam distillation.
use molecular distillation.
use high pressure distillation.
an azeotrope may be formed during distillation.

A

an azeotrope may be formed during distillation.

38
Q

Plate efficiency
is a function of the mass transfer between liquid and vapour.
increases due to foaming.
increases due to liquid entrainment.
increases due to weeping and dumping of liquid.

A

is a function of the mass transfer between liquid and vapour.

39
Q

Absorption accompanied by heat evolution results in
increased capacity of the absorber.
increase in equilibrium solubility.
decrease in equilibrium solubility.
none of these.

A

decrease in equilibrium solubility.

40
Q

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.

A

high pressure drop of the gas.

41
Q

For a distillation column operating at minimum reflux, the
concentration of liquid and vapour leaving a plate will be same.
reflux ratio will be maximum.
number of plates required will be maximum.
none of these.

A

number of plates required will be maximum.

42
Q

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)

A

MXo ln(Xo/XF)

43
Q

Flash distillation is suitable for the separation of components
having very close boiling points.
which form maximum boiling azeotrope.
having very wide boiling points.
which form minimum boiling azeotrope.

A

having very wide boiling points.

44
Q

In Mcabe-Thiele method, at infinite reflux ratio
number of plates is maximum.
overhead product is maximum.
both the operating lines coincide with the diagram.
none of these.

A

both the operating lines coincide with the diagram.

45
Q

Leaching rate is independent of the
agitation
temperature
particle size
none of these

A

none of these

46
Q

Use of packed towers for distillation is generally limited to the
small sizes.
multicomponent distillation.
high pressure operation.
vacuum distillation.

A

small sizes.

47
Q

Pick out the wrong statement.

The binary diffusivity in liquids is of the order of 10-5 cm2 /sec.

Molecular diffusion in solid is much faster than that in liquids.

Particles movement from higher concentration to lower concentration takes place in diffusion process.

According to Poiseuille’s law, the permeability decreases with increase in temperature for flow of a gas through a given capillary.

A

Molecular diffusion in solid is much faster than that in liquids.

48
Q

Which of the following decreases during evaporative cooling process with recirculated water supply ?
Wet bulb temperature
Relative humidity
Partial pressure of vapour
None of these

A

None of these

49
Q

Laboratory determination of the dif-fusivity of vapor is done by __________ method.
wetted wall column
Gilliland’s
Winkel mann’s
Wike’s

A

Winkel mann’s

50
Q

The minimum liquid rate to be used in an absorber corresponds to an operating line
of slope = 1
ofslope = 0.1
tangential to the equilibrium curve
none of these

A

tangential to the equilibrium curve

51
Q

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
cooled
humidified
both (a) & (b)
dehumidified

A

humidified

52
Q

For absorbing a sparingly soluble gas in a liquid, the
gas side co-efficient should be increased.
liquid side coefficient should be increased.
gas side co-efficient should be decreased.
liquid side co-efficient should be decreased.

A

liquid side coefficient should be increased.

53
Q

A natural draft cooling tower is filled with wooden grids, which covers about __________ percent of the tower height.
10-15
30-40
70-80
90-100

A

10-15

54
Q

The boiling points of pure components of a binary system __________ with increase in total pressure of the system.
decreases
increases
remains unchanged
may increase or decrease, depends on the system.

A

increases

55
Q

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

differential heat of adsorption.
heat of wetting.
integral heat of adsorption.
none of these.

A

differential heat of adsorption.

56
Q

Penetration theory relates the average mass transfer co-efficient (K) with diffusivity (D) as
K ∝D
K ∝sqrtD
K ∝D^1.5
K ∝D^2

A

K ∝sqrtD

57
Q

Desulphurisation of petrol is done in a
Bollman extractor
rotating disc extractor
packed extraction column
plate type extraction column

A

rotating disc extractor

58
Q

Chemisorption compared to physical absorption has
lower adsorption rate.
lower capacity of the solvent for the solute gas.
increased utilisation of stagnant zones of the liquid phase.
none of these.

A

increased utilisation of stagnant zones of the liquid phase.

59
Q

Rate of adsorption increases as the
temperature increases.
temperature decreases.
pressure decreases.
size of adsorbent increases.

A

temperature decreases.

60
Q

Pick out the system with maximum boiling azeotrope at 1 atm.
acetone chloroform
ethyl alcohol-water
benzene-ethyl alcohol
none of these

A

acetone chloroform

61
Q

At 750°K and 1 atm, the approximate value of Schmidt number for air is
0.01
0.1
1
10

A

0.1

62
Q

Calculation of mass transfer co-efficient is mostly/normally done using __________ theory.
surface renewal
film
penetration
none of these.

A

film

63
Q

The velocity, concentration and temperature boundary, for the boundary layer development on a flat plate during connective mass transfer will be same, if
NSc = 1
NSc = NPr = NLe
NPr = NLe
NSc = NLe

A

NSc = NPr = NLe

64
Q

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, mols/m2 , a: in-terfacial area per unit volume of tower)

G/Fg.a
Fg/G.a
G.a/Fg
L/Fg.G

A

G/Fg.a

65
Q

Which of the following is used for the concentration of rubber latex ?
Agitated film evaporator
Long tube vertical evaporator
Short tube evaporator
Calendria

A

Agitated film evaporator

66
Q

As the reflux ratio, in a continuous counter-current extraction is increased, the number of stages

increase
decrease
remain unchanged
can either increase or decrease, depends on the system

A

decrease

67
Q

In triangular co-ordinates, the ternery composition point falls __________ of the triangle.
in the corners
inside
on the sides
none of these.

A

inside

68
Q

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 raf-finate phase R containing A at xB = 0.5 and xR = 0.05 respectively. The total mass of the extract phase is (in Kg)
6.89
8.89
10
8.25

A

8.89

69
Q

Penetration theory states that the mass transfer co-coefficient is equal to (where, De is diffusivity and ‘t’ is time)
(De.t)^1/2
(De/t)^1/2
(4De/πt)^1/2
(4De/t)

A

(4De/πt)^1/2

70
Q

Reboiler is considered as one theoretical plate, because
of the assumption that vapour and liquid leaving the reboiler are in equilibrium.
vapour is recycled to the column.
reboiler itself contains one plate.
none of these.

A

of the assumption that vapour and liquid leaving the reboiler are in equilibrium.

ChELE 2024 (17 decks)

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