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CHEMICAL ENGINEERING DAY 2 > MASS TRANSFER > Flashcards

MASS TRANSFER Flashcards

FOR REVIEW HIKHIK

1
Q

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

low pressure drop and high hold up.
high pressure drop and low hold up.
low pressure drop and low hold up.
high pressure drop and high hold up.

A

low pressure drop and low hold up.

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2
Q

f the path of liquid across the plate is very long as in case of large diameter tower, Murphree efficiency can be __________ percent.
100
> 100
< 100
none of these

A

> 100

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3
Q

Raoult’s law is applicable to the

ideal solutions
real solutions
mixture of water and alcohol
non-ideal gases

A

ideal solutions

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4
Q

Weeping in a distillation column

increases tray efficiency.
provides large interfacial surface for mass transfer.
results due to very high gas velocity.
results due to very low gas velocity.

A

results due to very low gas velocity.

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5
Q

In case of binary distillation, increasing the reflux ratio above optimum does not result in the increase of

area between operating line and 45° diagonal x-y diagram.
condenser and reboiler surfaces.
tower cross-section.
none of these.

A

area between operating line and 45° diagonal x-y diagram.

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6
Q

molal diffusivity.
volumetric co-efficient.
mass transfer co-efficient.
none of these.

A

mass transfer co-efficient.

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7
Q

In McCabe-Thiele method, at infinite reflux ratio —–

the overhead product is minimum.
both the operating lines coincide with diagonal.
both (a) and (b).
neither (a) nor (b).

A

the overhead product is minimum.

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8
Q

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

increases
decreases
remains same
may increase or decrease ; depends on individual design
Answer: Option

A

increases

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9
Q

Plate towers are preferred to packed towers, when large temperature changes are involved, because of the reason that the

packing may be crushed due to thermal expansion/contraction of the components of the equipment.
pressure drop in the equipment will be very high.
viscosity variation of the fluids may cause channeling/flooding.
none of these.

A

packing may be crushed due to thermal expansion/contraction of the components of the equipment.

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10
Q

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

more
less
same
either more or less; depends on the system

A

same

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11
Q

Out of the following gas-liquid contacting devices, for a given set of operating conditions, gas pressure drop is the least in __________ tower.

wetted wall
bubble cap
perforated tray
packed

A

wetted wall

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12
Q

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

benzene-toluene
ethyl alcohol-water
hydrochloric acid-water
all (a), (b) and (c)

A

ethyl alcohol-water

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13
Q

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

rotary
cylinder
drum
freeze

A

rotary

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14
Q

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

inversely
linearly
exponentially
none of these

A

linearly

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15
Q

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

Sherwood
Schmidt
Peclet
Stanton

A

Sherwood

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16
Q

Molarity is defined as the number of gm moles of solute per __________ of solution.

liter
kg
gm
c.c

A

liter

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17
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)

less number of trays are required.
composition of the residue remains unchanged.
more number of trays are required but the residue composition remains unchanged.
more number of trays are required and the residue composition is more dilute in methanol.

A

less number of trays are required.

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18
Q

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

exponential
parabolic
linear
cubic

A

exponential

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19
Q

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

Water-hydrochloric acid.
Acetone-carbon disulphide.
Water-ethyl alcohol.
n-heptane-n-octane.

A

Water-hydrochloric acid.

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20
Q

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

Stanton
Sherwood
Peclet
none of these

A

Peclet

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21
Q

he binary diffusivity in gases and liquids vary respectively as

T3/2 and T
T and T3/2
T and T3/2
T3/2 and T

A

T3/2 and T

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22
Q

Pick out the correct statement.

The slope of the stripping line is always less than unity.

For a given separation in a binary distillation column, with increase in reflux ratio (above the minimum reflux ratio), the fixed cost of the distillation column first increases and then decreases.

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

Kremsor-Brown-Souder’s equation is used to calculate the efficiency of a plate tower.

A

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

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23
Q

Pick out the correct statement.

Dialysis process is used for the production of fresh water from brine.

Electrodialysis is used in the manufacture of NaOH.

Electrodialysis is used for the refining/purification of petrol.

both (b) and (c).

A

Electrodialysis is used in the manufacture of NaOH.

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24
Q

Pick out the correct statement.

Bound moisture is removed during constant rate drying period.

Free moisture is removed during falling rate drying period.

The sum of free moisture and equilibrium moisture in a solid is called the critical moisture.

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

A

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

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25
Q

Very tall packed towers are divided into series of beds to—-

reduce the overall pressure drop
avoid channeling
reduce liquid hold-up
avoid flooding

A

avoid channeling

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26
Q

Moisture contained by a substance in excess of the equilibrium moisture is called the __________ moisture.
unbound
free
critical
bound

A

free

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27
Q

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

increases
decreases
remains same
either (a) or (b), depends on the system

A

decreases

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28
Q

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

suction pump
compressed air jet
steam jet ejector with a barometric condenser
none of these

A

steam jet ejector with a barometric condenser

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29
Q

On moving the feed line (q-line) from saturated liquid feed (vertical position) to saturated vapor feed (horizontal feed), if the slope of both the operating lines are to be increased, then it will result in

greater degree of separation with a fixed number of trays
increased reboiler load
increased reflux ratio
None of these.

A

greater degree of separation with a fixed number of trays

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30
Q

__________ column is the most suitable for achieving the best performance for mass transfer operations involving liquid with dispersed solids.

Wetted wall
Packed
Plate
Spray

A

Plate

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31
Q

Deairation (removal of O2) of water is done by

rectification
absorption
ion-exchange
adsorption

A

ion-exchange

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32
Q

Pick out the wrong statement.

The mole fraction of solute is directly proportional to the molality of a ‘dilute’ solution.

For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both components is nonlinear in the case of steady state unimolal unidirectional diffusion.

Azeotropes obey Raoult’s law at all temperature.

The relative volatility of a binary mixture at the azeotropic composition is 1.

A

Azeotropes obey Raoult’s law at all temperature.

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33
Q

Make up water is supplied during cooling tower operation to compensate for water losses due to
evaporation
blowdown
entrainment
all (a), (b)&(c)

A

ALL

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34
Q

A minimum boiling azeotrope is exemplified by

toluene-benzene
acetone-carbon disulphide
water-isobutyl alcohol
none of these

A

acetone-carbon disulphide

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35
Q

Which of the following solutions will follow Raoult’s law most closely ?

A solution of benzene, toluene and oxylene.

35% solution of camphor in water.

35% solution of NH3 in water.

A solution of polar organic compounds (not of homologs of a series).

A

A solution of benzene, toluene and oxylene.

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36
Q

Use of raschig rings in place of crushed stones as packing in packed beds (other things being same)

increases pressure drop, increases surface area.

increases pressure drop, decreases surface area.

decreases pressure drop, increases surface area.

decreases pressure drop, decreases surface area.

A

decreases pressure drop, increases surface area.

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37
Q

As complete saturation of an adsorbent is approached, the differential heat of adsrop-tion approaches

that of normal condensation.
integral heat of adsorption.
zero.
none of these.

A

that of normal condensation.

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38
Q

‘Absorption with chemical reaction’ is involved in the removal of

carbon dioxide from gaseous stream using alkaline solution.

benzol from coke oven gas using solar oil/wash oil.

ammonia from coke oven gas using refrigerated water.

tar from coke oven gas in primary gas coolers using chilled water.

A

carbon dioxide from gaseous stream using alkaline solution.

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39
Q

The-relative volatility for separation of a non-ideal binary mixture by distillation should be
0
1
> 1
< 1

A

> 1

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40
Q

Pick out the wrong statement:

Reboiler is not used in open steam distillation.
The separation of solutes of different molecular sizes in a liquid solution by use of a suitable membrane is called dialysis.
Freeze drying is used for the drying of fish.
Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.

A

Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.

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41
Q

In paper industry, paper is dried in a __________ dryer.

tunnel
heated cylinder
conveyor
festoon

A

heated cylinder

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42
Q

Pick out the wrong statement.
Critical moisture content is not a property of the material itself.
A sharp increase in pressure drop gives an indication of the flooding in a distillation column.
Separation of components is not possible in liquid extraction, if selectivity is unity.
Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.

A

Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.

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43
Q

Only small amount of evaporation of water produces large cooling effects because of its

large latent heat
low viscosity
small latent heat
none of these

A

large latent heat

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44
Q

The most common packing used in industrial operations is __________ rings.
raschig
lessing
cross-partition
single spiral

A

raschig

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45
Q

When the feed to a distillation column is a saturated liquid, slope of the feed line is

zero
unity
infinity
none of these

A

infinity

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46
Q

Leaching of sugar from sugar beets is done by

hot water
hexane
dilute H2SO4
lime water

A

hot water

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47
Q

Absorption factor method is used to calculate the number of ideal stages, when

operating line lies above the equilibrium line.
operating line lies below the equilibrium line.
both operating and equilibrium lines are parallel.
pressure drop in the column is very high.

A

both operating and equilibrium lines are parallel.

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48
Q

Flights in a rotary dryer are provided to

lift and shower the solids thus exposing it thoroughly to the drying action of the gas.
reduce the residence time of solid.
increase the residence time of the solid.
none of these.

A

lift and shower the solids thus exposing it thoroughly to the drying action of the gas.

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49
Q

If the solubilities of different components (in a liquid-liquid extraction system) increase with rise in temperature, then the temperature above which they dissolve completely is known as the critical solution temperature (CST or consolute temperature). If solubilities increase with decrease in temperature, then CST is the temperature below which they dissolve completely. If a binary system has no critical solution temperature, it implies that

the system comprises of partially miscible liquids.
the system comprises of miscible liquids.
the system comprises of an azeotrope.
on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.

A

on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.

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50
Q

Dry bulb temperature of unsaturated air is more than its __________ temperature.
dew point
wet bulb
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’

A

both ‘a’ & ‘b’

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51
Q

The reciprocal of stripping factor is termed as

selectivity index
relative volatility
absorption factor
Murphree efficiency

A

absorption factor

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52
Q

Ponchan-Savarit method analyses the fractional equipment based on

enthalpy balance only.
material balance only.
both enthalpy and material balances.
the assumption of constant molal overflow.

A

both enthalpy and material balances.

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53
Q

The binary diffusivity in gases at atmospheric conditions is about

10^-9 cm/sec
10^-1 cm^2/sec
10^-3 sec/cm
10^-4 cm^2/sec^2

A

10^-1 cm^2/sec

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54
Q

Percentage saturation is __________ the relative saturation.

always smaller than
always greater than
not related to
none of these

A

always smaller than

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55
Q

In case of a desorber (stripper), the

operating line always lies above the equilibrium curve.
operating line always lies below the equilibrium curve.
temperature remains unaffected.
temperature always increases.

A

operating line always lies below the equilibrium curve.

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56
Q

What is the reflux ratio at total reflux ?

Zero
Infinity
Unity
Data insufficient

A

Infinity

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57
Q

Under conditions of flooding in packed tower, the gas pressure drop

decreases rapidly
increases rapidly
remains constant
is maximum

A

is maximum

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58
Q

For achieving rapid drying rate in a spray dryer, the diameter of the particles in the feed should be in the range of __________ microns (1 mm = 1000 microns).

1-5
10-60
200-300
> 500

A

10-60

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59
Q

The change in enthalpy per unit weight of adsorbed gas when adsorbed on gas free or “outgassed” adsorbent to from a definite concentration of adsorbate is called its

integral heat of adsorption.
heat of wetting.
differential heat of adsorption.
heat of normal condensation.

A

integral heat of adsorption.

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60
Q

The minimum number of theoretical plates is required for achieving a given separation in distillation column with

no reflux
total reflux
zero reflux ratio
minimum reflux ratio

A

total reflux

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61
Q

A good solvent used for absorption should not have very high

viscosity
vapor pressure
freezing point
all (a), (b) & (c)

A

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

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62
Q

In a counter-current liquid extractor

both liquids flow at fixed rate.
both liquids can have any desired flow rate.
only one of the liquids may be pumped at any desired rate.
liquid’s flow rate depends upon the temperature and pressure.

A

only one of the liquids may be pumped at any desired rate.

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63
Q

The wetted wall tower is used to determine
individual mass transfer co-efficient (M.T.C.) in gaseous system.
M.T.C. of individual components in a liquid-liquid system.
M.T.C. of liquid in liquid-gas system.
the overall M.T.C. of the system.

A

individual mass transfer co-efficient (M.T.C.) in gaseous system.

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64
Q

Weight of 1 cum of humid air as compared to 1 cum of dry air, under the same conditions, is

less
more
same
unpredictable

A

less

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65
Q

Positive deviation from Raoult’s law means a mixture whose total pressure is

greater than that computed for ideality.
less than that computed for ideality.
less than the sum of the vapour pressure of the components.
none of these.

A

greater than that computed for ideality.

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66
Q

With increase in gas rate, the number of transfer units, NtoG, for a fixed degree of absorption by a fixed amount of solvent —-

increases
decreases
decreases linearly
remains unaffected

A

increases

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67
Q

Prandtl number for water at 20°C is about

7
70
0.7
150.

A

7

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68
Q

Boiling point diagram is

not affected by pressure.
affected by pressure.
a plot of temperature vs. liquid composition.
a plot of temperature vs. vapour composition.

A

affected by pressure.

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69
Q

Steam distillation is used to

reduce the number of plates.
avoid thermal decomposition of a component.
increase the efficiency of separation.
increase the total pressure of distillation.

A

avoid thermal decomposition of a component.

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70
Q

Freundlich equation applies to the adsorption of solute from

dilute solutions, over a small concentration range.
gaseous solutions at high pressure.
concentrated solutions.
none of these.

A

dilute solutions, over a small concentration range.

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71
Q

For ethanol-water system, the lowering of distillate quality from 95% to 92% will cause __________ plate requirement.

no change in theoretical
marginal decrease in the number of
major decrease in the number of
none of these

A

marginal decrease in the number of

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72
Q

The apex of an equilateral-triangular coordinate (in ternary liquid system) represents a/an

pure component
binary mixture
ternary mixture
insoluble binary system

A

pure component

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73
Q

A slurry is to be dried to produce flaky solid. Which dryer would you recommend?

Spray dryer
Drum dryer
Rotary dryer
Dielectric dryer

A

Spray dryer

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74
Q

Which of the following psychrometric processes is followed by water vapour laden unsaturated air, when it is passed through solid or liquid adsorbent ?

Cooling and dehumidification.
Heating and dehumidification at almost constant wet bulb temperature.
Dehumidification with dry bulb temperature remaining constant.
None of these.

A

Heating and dehumidification at almost constant wet bulb temperature.

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75
Q

The value of NA/(NA + NB) for steady state molecular diffusion of gas ‘A’ through non-diffusing gas ‘B’ is
1
∞
0.5
2

A

1

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76
Q

Pick out the wrong statement

Co-current absorbers are usually used, when the gas to be dissolved in the liquid is a pure substance.

In case of gas absorption, HETP is equal to HTU, when both the operating line & the equilibrium lines are parallel.

Hatta number is important in case of gas absorption with chemical reaction.

In actual practice, absorption is an endothermic process, while stripping is an exothermic process.

A

In actual practice, absorption is an endothermic process, while stripping is an exothermic process.

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77
Q

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.

continuous
steam
azerotropic
none of these

A

steam

78
Q

Large scale drying of wheat is done in a __________ dryer.

fluidised bed
spouted bed
tray
vacuum rotary

A

spouted bed

79
Q

Azeotropic distillation is employed to separate —-

constant boiling mixture.
high boiling mixture.
mixture with very high relative volatility.
heat sensitive materials.

A

constant boiling mixture.

80
Q

The drying time between fixed moisture content within diffusion controlled ‘falling rate period’ is proportional to (assuming that drying occurs from all surfaces of the solid) (where, T = thickness of the solid )
sqrt. T
T
T^2
T^3

A

T^2

81
Q

At the boiling point of the liquid at the prevailing pressure, the saturated absolute humidity becomes
1
0
∞
none of these

A

∞

82
Q

Use of natural draft cooling tower is practised, when the air has low

humidity
temperature
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’

A

both ‘a’ & ‘b’

83
Q

Pressure drop through plate tower as compared to that through packed tower, for the same duty will be

less
more
equal
either (a) or (b); depends on the packing height

A

more

84
Q

Dimension of mass diffusivity is the same as that of

kinematic viscosity
dynamic viscosity
surface tension
pressure

A

kinematic viscosity

85
Q

Dorr thickener is an equipment used for

classification
sedimentation
clarification
leaching

A

sedimentation

86
Q

Steam distillation is used to separate

azeotropes.
high boiling substances from nonvolatile impurities.
heat sensitive materials.
mixtures of low relative volatility.

A

high boiling substances from nonvolatile impurities.

87
Q

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
q > 1
q < 1
q = 1
q = 0

A

q = 1

88
Q

Which of the following is an undesirable property in a tower packing ?
Large surface per unit volume.
Large free cross-section.
Low weight per unit volume.
Large weight of liquid retained.

A

Large weight of liquid retained.

89
Q

Water entrained by circulating air in cooling towers is termed as

drift
blow down
vapor load
none of these.

A

drift

90
Q

With increase in temperature, the rate of leaching increases, because the

diffusivity of solute increases.
viscosity of solvent decreases.
thermal conductivity of solute increases.
none of these.

A

diffusivity of solute increases.

91
Q

Humidity chart is useful for the solution of problems concerning condensation, vaporisation and air conditioning. At a given dry bulb temperature, value of humidity obtained from the humidity chart directly, is in terms of __________ humidity.

molal
relative
percentage
none of these

A

molal

92
Q

The Kundsen diffusivity is proportional to (where, T = absolute temperature)
sqt T
T^2
T
T^4

A

sqt T

93
Q

In an absorption coloumn, the flooding velocity for random packing is __________ that for stacked/regular packing.

greater than
smaller than
equal to
either (a), or (b) ; depends on the type of packing

A

smaller than

94
Q

The relation among various mass transfer co-efficients (M.T.C) for ideal gases is given by (where, Kc & Km are M.T.C. for equimolar counter diffusion with concentration & mole fraction respectively as the driving force. and, Kp = M.T.C. for diffusion of a gas through a stagnant inert gas with pressure as driving force.)

Kc = Kp = Km
Kc = Kp/RT = Km . RT/P
Kc = Kp . RT = Km . RT/p
none of these

A

Kc = Kp . RT = Km . RT/p

95
Q

With increase in temperature, the leaching rate increases because of the

increased diffusivity.
decreased viscosity of liquid.
both (a) and (b).
neither (a) nor (b).

A

both (a) and (b).

96
Q

Leaching of uranium ore and gold ore is done in

centrifugal extractor
Pachuka tanks
Bollman extractor
none of these

A

Pachuka tanks

97
Q

Blowdown in a cooling tower

means discarding a small fraction of circulating water to prevent and limit the concentration of salt and impurities.

increases the scale forming tendencies of water.

is undesirable.

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

A

means discarding a small fraction of circulating water to prevent and limit the concentration of salt and impurities.

98
Q

Antibiotics are best handled in a

Podbielniak extractor.
sieve tray contractor.
rotating disc contactor.
pulsed column extractor.

A

Podbielniak extractor.

99
Q

The fixed cost of a distillation column at minimum reflux ratio is
minimum
infinite
optimum
none of these

A

infinite

100
Q

__________ extractor uses centrifugal force for separating the two phases.

Treybal
Schiebel
Podbielniak
None of these

A

Podbielniak

101
Q

In a binary distillation column, if the feed contains 40 mole % vapour, the q line will have a slope of
1.5
-0.6
-1.5
0.6

A

-1.5

102
Q

Pick out the wrong statement.

Mechanical agitation is required, if the system has low interfacial tension.

Seive tray towers are generally used for systems having low interfacial tension.

When Henry’s law constant is very small, then the mass transfer rate is controlled by the gas film resistance.

Taylor-Prandtl analogy for heat and mass transfer considers the transfer through both laminar and turbulent layers.

A

Mechanical agitation is required, if the system has low interfacial tension.

103
Q

Acetic acid will be most economically separated from a dilute solution of acetic acid in water by

solvent extraction
continuous distillation
evaporation
absorption

A

solvent extraction

104
Q

Design calculation for multiple component distillation is done by

Ponchon-Savarit method
Mccabe-Thiele method
enthalpy concentration method
tray to tray calculations.

A

tray to tray calculations.

105
Q

To get high tray efficiency

interfacial surface between liquid and gas phase should be large.
time of contact between the two phases should be less.
gas velocity should be very low.
liquid entrainment should be severe.

A

interfacial surface between liquid and gas phase should be large.

106
Q

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
D/a
D/2a
proportional to sqrt. D
dependent on the Reynolds number

A

proportional to sqrt. D

107
Q

Solvent extraction is the terminology applied to the liquid-liquid extraction, which is preferred for the separation of the components of liquids, when

extracting solvent is cheaply & abundantly available.
one of the liquid components is heat sensitive.
viscosity of liquid components is very high.
one of the liquid components has very high affinity towards the solvent.

A

one of the liquid components has very high affinity towards the solvent.

108
Q

Inside the distillation column, the

driving force for the vapour flow is the pressure drop.
liquids are not always at their bubble points.
pressure increases gradually from bottom to the top of the column.
none of these

A

driving force for the vapour flow is the pressure drop.

109
Q

Diffusivity in concentrated solutions differs from that in dilute solutions, because of the changes in

viscosity with concentration.
degree of ideality of the solution.
both (a) and (b).
neither (a) nor (b).

A

both (a) and (b).

110
Q

Occurrence of ‘case hardening’ during drying of a high moisture solid cake __________ the drying rate.

increases
decreases
does not affect
exponentially increases

A

decreases

111
Q

Which of the following is not a continuous drier ?
Drum drier
Spray drier
Tunnel drier
Tray drier

A

Tray drier

112
Q

Humidification involves mass transfer between a pure liquid phase and a fixed gas, which is

insoluble in the liquid
soluble in the liquid
non-ideal in nature
at a fixed temperature

A

insoluble in the liquid

113
Q

__________ is the temperature at which a gas-vapor mixture becomes saturated, when cooled at constant total pressure out of contact with a liquid.

Dew point
Bubble point
Dry bulb temperature
Wet bulb temperature

A

Dew point

114
Q

Rate of leaching increases with increasing

temperature
viscosity of solvent
pressure
size of the solid

A

temperature

115
Q

An azeotropic mixture is a __________ mixture.

binary
ternary
constant boiling point
none of these

A

constant boiling point

116
Q

Molecular seives are regenerated by heating to __________ °C.

< 150
200-330
> 500
> 1000

A

200-330

117
Q

In a counter-current extractor, as the axial mixing increases, the extraction efficiency

increases
decreases
remains unchanged
depends on the pressure of the system

A

decreases

118
Q

Heat sensitive materials like certain pharmaceuticals and food stuffs can be dried in a/an __________ dryer.

indirect tray
spray
freeze
none of these

A

freeze

119
Q

In extractive distillation, solvent is

added to alter the relative volatility of the mixture.
of high volatility.
present in overhead stream.
of high viscosity to give high tray efficiency.

A

added to alter the relative volatility of the mixture.

120
Q

Radioactive nuclear waste is treated in

mixer-settler extractor
rotating-disc contactor
pulsed column extractor
Bollman extractor

A

pulsed column extractor

121
Q

Large scale drying of sugar is done in a __________ dryer.

spouted bed
tray
rotary
truck

A

rotary

122
Q

__________ temperature is the steady state temperature attained by a small amount of liquid evaporating into a large quantity of unsaturated gas-vapor mixture.

Dry bulb
Wet bulb
Dew point
none of these

A

Wet bulb

123
Q

The drying time between fixed moisture contents within the ‘constant rate period’ is proportional to (assuming that drying occurs from all surfaces of the solid) (where, T = thickness of the solid )

sqrt. T
T
T^1.5
T^3

A

T

124
Q

__________ equation applies to diffusivities in liquids.
Gilliland
Hirschfelder
Wilke and Chang
none of these

A

Gilliland

125
Q

A packed tower compared to a plate tower for a particular mass transfer operation

incurs smaller pressure drop.
allows installation of cooling coils.
is less costly when built in large sizes/diameters.
is more suitable, if suspended solids are present in fluid streams.

A

incurs smaller pressure drop.

126
Q

Which of the following is the most commonly used leaching solvent in vegetable oil industry?

Phenol
Hexane
Furfurol
Liquid SO2

A

Hexane

127
Q

Large quantity of silica gel is normally dried in a __________ dryer.

freeze
through circulation
rotary vacuum
tray

A

through circulation

128
Q

For the same system, if the same liquid used in an absorber is decreased, the tower height will

increase
decrease
remain unaffected
decrease or increase ; depends on the type of liquid

A

increase

129
Q

Hydrogenation of oil is carried out in a/an __________ in Vanaspati manufacturing plant.

agitated vessel
sieve tray column
bubble cap column
packed tower

A

agitated vessel

130
Q

Sides of equilateral-triangular co-ordinates (on which ternary liquid system is plotted) represent

a pure component.
a binary mixture.
a ternary mixture.
partially miscible ternary system.

A

a binary mixture.

131
Q

In distillation column design, the McCabe-Thiele procedure is inadequate and a Ponchan-Savarit procedure is needed, when

saturated feed is not used.
an azeotrope forms.
the latent heat of vaporisation of the more and less volatile components are greatly different.
a total condenser is used.

A

a total condenser is used.

132
Q

In an interphase mass transfer process, the lesser the solubility of a given solute in a liquid, the higher are the chances that the transfer process will be

liquid phase resistance-controlled.
gas phase resistance controlled.
impossible.
driven by a non-linear driving force.

A

gas phase resistance controlled.

133
Q

As the reflux ratio decreases, the

separation becomes more efficient.
number of plates increases.
column diameter increases.
none of these.

A

number of plates increases.

134
Q

Which of the following equipments is not used for gas dispersion ?

Agitated vessels
Bubble cap tray towers
Perforated sieve tray towers
Spray towers

A

Spray towers

135
Q

One mole feed of a binary mixture of a given composition is flash vaporised at a fixed P and T. If Raoult’s law is obeyed, then changing the feed composition would effect

the product composition but not the fraction vaporised.

the product composition as well as the fraction vaporised.

the fraction vaporised but not the product composition.

neither the product composition nor the fraction vaporised.

A

the fraction vaporised but not the product composition.

136
Q

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

decreases
remains unchanged
increases
decreases exponentially

A

increases

137
Q

Which of these columns incurs the lowest pressure drop ?

Packed column (with stacked packing)
Packed column (with dumped packing)
Bubble plate column
Pulse column

A

Packed column (with stacked packing)

138
Q

In the desorption of highly soluble gas from the liquid, the main resistance will be in the __________ phase.
gas
liquid
both (a) & (b)
neither (a) nor (b)

A

liquid

139
Q

If G = insoluble gas in gas stream and L = non-volatile solvent in liquid stream, then the slope of the operating line for the absorber is
L/G
G/L
always < 1
none of these

A

L/G

140
Q

Which of the following remains constant during evaporative cooling process with recirculated water supply ?

Relative humidity
Partial pressure of vapour
Wet bulb temperature
None of these

A

Wet bulb temperature

141
Q

For stripping of a gas in a counter current stripper, the operating line

lies above the equilibrium curve.
lies below the equilibrium curve.
can lie above or below the equilibrium curve.
is always parallel to the equilibrium curve.

A

can lie above or below the equilibrium curve.

142
Q

Which of the following same diameter columns gives lowest pressure drop per unit height ?

Bubble-cap column
Sieve-plate column
Packed column (stacked)
Randomly packed column

A

Packed column (stacked)

143
Q

Diffusion in concentrated solutins differs from that in dilute solutions, because of the change in the __________ with the concentration of the solution.

degree of ideality
viscosity
both ‘a ‘& ‘b’
neither ‘a’ nor ‘b’

A

both ‘a ‘& ‘b’

144
Q

Stage efficiency in a leaching process depends on the

time of contact between the solid and the solution
rate of diffusion of the solute through the solid and into the liquid
both (a) and (b)
vapour pressure of the solution

A

both (a) and (b)

145
Q

Operating velocity in a packed tower is usually __________ the flooding velocity.

half
twice
equal to
more than

A

half

146
Q

The Knudsen diffusivity is dependent on the

molecular velocity only.
pore radius of the catalyst only.
molecular mean free path only.
molecular velocity and por radius of the catalyst.

A

molecular velocity and pore radius of the catalyst.

147
Q

Minimum possible diameter of a packed coloumn is decided mainly by the

flooding
gas viscosity
liquid density
liquid hold up

A

flooding

148
Q

Solvent used in extractive distillation

is of low volatility.
forms a low boiling azeotrope.
forms a high boiling azeotrope.
does not alter the relative volatility of the original components.

A

forms a low boiling azeotrope.

149
Q

Capacity of a rotary dryer depends on its

r.p.m
inclination with ground surface
both (a) and (b)
neither (a) nor (b)

A

both (a) and (b)

150
Q

The cooling effect in a cooling tower can be speeded up by

increasing the air velocity and area of exposed wet surface.
reducing the barometric pressure.
reducing the humidity of the air.
all (a), (b) and (c).

A

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

151
Q

Perforated plate towers are unique for solvent extraction because, they provide

higher contact area.
better contact of the phase.
repeated coalescence & redispersion of the drop phase.
none of these.

A

repeated coalescence & redispersion of the drop phase.

152
Q

In case of absorption & stripping, the interface of the liquid & gas phases are present in equilibrium, when the diffusional resistance of __________ is zero.

interface
gas phase
liquid phase
all ‘a’, ‘b’ & ‘c’

A

interface

153
Q

Swenson-Walker crystalliser is a __________ unit

continuous
batch
semi-batch
cooling (adiabatic)-cum-evaporation

A

continuous

154
Q

With increase in temperature, the mutual solubility of two liquids ____________.

increases
decreases
remains unchanged
decreases exponentially

A

increases

155
Q

The relative volatility of a binary mixture at the azeotropic composition is
1
> 1
0
∞

A

1

156
Q

Relative volatility varies with the concentration of component for an ideal solution. The relative volatity of a binary mixture may be defined as the ratio of vapor pressure of component ‘A’ to that of component ‘B’, when _____________.

only vapor phase follows Raoult’s law.
only liquid phase obeys Dalton’s law.
liquid phase obeys Dalton’s law and vapor phase obeys Raoult’s law.
Vapor phase obeys Dalton’s law and liquid phase obeys Raoult’s law.

A

Vapor phase obeys Dalton’s law and liquid phase obeys Raoult’s law.

157
Q

__________ extractor is used for the concentration of radioactive nuclear waste.
Pulsed column
Seive plate
Mixer-settler
Ballman

A

Pulsed column

158
Q

Moisture content of a substance when at equilibrium with a given partial pressure of the vapour is called the __________ moisture.

free
unbound
equilibrium
bound

A

equilibrium

159
Q

All moisture in a non-hygroscopic material is the __________ moisture.

free
equilibrium
unbound
bound

A

unbound

160
Q

Pick out the correct relationship. (where, Ri = internal reflux ratio Ro = external reflux ratio. )

(1 + Ro) = Ro/Ri
(1 - Ro) = Ro/Ri
(1 + Ri) = Ro/Ri
(1 - Ri) = Ro/Ri

A

(1 + Ro) = Ro/Ri

161
Q

Separation of __________ employs gaseous diffusion process.

N2 and O2 from air
isotopes of uranium
isotopes of helium
SO2 and air

A

isotopes of uranium

162
Q

For water-ethanol system, the minimum reflux ratio

is computed from the slope of the upper operating line that is tangent to the equilibrium curve.
is computed from the intercept of the operating line.
cannot be computed.
is the optimum reflux ratio.

A

is computed from the slope of the upper operating line that is tangent to the equilibrium curve.

163
Q

Experimental determination of __________ is done by wetted wall column method.

diffusion co-efficient
mass transfer co-efficient
NTU
none of these

A

mass transfer co-efficient

164
Q

In liquid extraction, if the selectivity is unity, then

separation of the constituents is the most effective.
no separation will occur.
amount of solvent required will be minimum.
solvent flow rate should be very low.

A

no separation will occur.

165
Q

Paper industry employs __________ driers.

cylinder
rotary
spray
fluidised bed

A

cylinder

166
Q

Leaching of coarse solid lumps is also termed as

decoction
dissolution
percolation
agitation and settling

A

percolation

167
Q

The main reason for dividing a tall packed tower into series of small towers is to

minimise the overall pressure drop.
avoid flooding.
reduce liquid hold up.
avoid channeling.

A

avoid channeling.

168
Q

Co-current absorbers are usually used when the gas to be dissolved in the liquid is

sparingly soluble
highly soluble
a pure substance
a mixture

A

a pure substance

169
Q

At what percentage (by volume) of alcohol composition, it forms an azeotrope with water ?

90
91.5
95
99

A

95

170
Q

Measurement of the interfacial area of mass transfer is achieved easily & accurately in case of a __________ coloumn.

spray
packed
bubble cap plate
wetted wall

A

wetted wall

171
Q

Mass transfer co-efficient is defined as

Flux = Co-efficient/concentration difference.
Co-efficient = Flux/concentration difference.
Flux=concentration difference/co-effi-cient.
none of these.

A

Co-efficient = Flux/concentration difference.

172
Q

When an unsaturated air-water mixture is heated at constant pressure, then

the partial pressure of water vapour increases.
the specific humidity decreases.
The relative humidity increases.
the relative humidity decreases.

A

the relative humidity decreases.

173
Q

At a fixed pressure, the humidity depends upon the partial pressure of vapor in the mixture. Humidity of a vapour free gas is __________ percent.

100
0
50
between 0 and 100

A

0

174
Q

Large scale usage of flash distillation is practised in

soap manufacturing
ammonia synthesis plant
polymerisation industry
petroleum refinning

A

petroleum refinning

175
Q

High pressure at the bottom of a distillation tower handling heat sensitive materials results in

thermal decomposition of bottoms.
increased relative volatility.
erosion of the tower.
very efficient operation.

A

thermal decomposition of bottoms.

176
Q

Alcohol is dehydrated using __________ distillation.

extractive
azeotropic
steam
molecular

A

azeotropic

177
Q

Separation of two volatile liquids by distillation makes use of their

selectivity
relative volatility
solubility
density difference

A

relative volatility

178
Q

Dried finished product sampled from various parts of a __________ dryer exhibits non-uniformity in the moisture content.

rotary
tray
freeze
none of these

A

tray

179
Q

__________ is used as an ‘entrainer’ for the separation of acetic acid-water mixture by distillation.

Furfural
Benzol
Butyl acetate
Hexane

A

Butyl acetate

180
Q

Rotary dryers cannot handle __________ materials.

free flowing
dry
sticky
grannular

A

sticky

181
Q

An example of elution is

separation of uranium oxide from its ore by H2SO4 in a Pachuca tank.
separation of sugar from sugar beet by hot water.
dissolution of tannin out of tree barks by water.
recovery of vegetable oils from seeds.

A

separation of uranium oxide from its ore by H2SO4 in a Pachuca tank.

182
Q

The operating line for an absorber is curved, when plotted in terms of

mole fractions
mole ratios
partial pressure
mass fractions

A

partial pressure

183
Q

For continuous drying of grannular or crystalline material, the dryer used is the __________ dryer.

tunnel
tray
rotary
none of these

A

rotary

184
Q

Moisture in a substance exerting an equilibrium vapour pressure less than that of pure liquid at the same temperature is called the __________ moisture.

bound
unbound
critical
none of these

A

bound

185
Q

For a binary mixture with low relative volatility, continuous rectification to get pure products will require

low reflux ratio
less number of trays
small cross-section column
high reflux ratio

A

high reflux ratio

186
Q

Detergent solution is dried to a powder in a

spray dryer
spouted bed dryer
tunnel dryer
pan open to atmosphere

A

spray dryer

187
Q

During bottling of cold drinks (e.g. Pepsi), the main resistance to mass transfer for the absorption of carbon dioxide in water lies in the

gas film
liquid film
liquid-gas interface
none of these

A

liquid film

188
Q

The overall mass transfer co-efficient for the absorption of SO2 in air with dilute NaOH solution can be increased substantially by

increasing the gas film co-efficient.
increasing the liquid film co-efficient.
increasing the total pressure.
decreasing the total pressure.

A

increasing the gas film co-efficient.

189
Q

Flooding results in

high tray efficiency
low tray efficiency
high gas velocity
good contact between the fluids

A

low tray efficiency

190
Q

he suitable evaporator for concentration of foaming liquids is a __________ evaporator.

long tube
short tube
vacuum
falling film

A

long tube

191
Q
A

CHEMICAL ENGINEERING DAY 2 (2 decks)

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