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Philippine Chemical Engineering Licensure Examination Day 2 Separation Processes > IndiaBIX Chemical Engineering: Mass Transfer Section 6 > Flashcards

IndiaBIX Chemical Engineering: Mass Transfer Section 6 Flashcards

1
Q

When both the fluids flow concurrently in an absorber, the slope of the operating line is
- ve
+ ve
1
-1

A
  • ve
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2
Q

The percentage humidity is less than the relative humidity only at __________ percent humidity.
zero
hundred
both zero and hundred
none of these

A

both zero and hundred

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3
Q

Back-trapping in a distillation column
increases tray efficiency.
decreases tray efficiency.
reduces pressure drop.
is desirable, as it provides improved vapour-liquid contact.

A

decreases tray efficiency.

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4
Q

Flooding in a vapor-liquid contacting equipment occurs in a tray, when the pressure drop through a tray is __________ the liquid head available in the downcomer.
less than
more than
same as
very much less

A

more than

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5
Q

Milk is dried usually in a __________ dryer.
freeze
spray
tray
rotary

A

spray

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6
Q

At a given equilibrium pressure, with increase in temperature, the concentration of adsorbed gas on solid adsorbant
increases
decreases
remains unchanged
increases exponentially

A

decreases

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7
Q

Which of the following adsorbent is used to decolourise yellow glycerine ?
Silica gel
Alumina
Fuller’s earth
Activated carbon

A

Activated carbon

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8
Q

Which of the following liquid temperature (T) Vs. vapor-gas mixture enthalpy (H) diagram is valid for humidification operation?
none of these.

A

B

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9
Q

In a distillation column, with increase in the reflux ratio, the heat removed in the cooler
increases.
decreases.
remains unaffected.
and the heat required in reboiler decreases.

A

increases.

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10
Q

Pick out the wrong statement.
Constant pressure distillation can not separate an azeotropic mixture.
Relative volatility of a binary mixture changes appreciably with the minor change in temperature.
The relative volatility of a binary mixture at azeotropic composition is unity.
Flash distillation is practised on wide spread scale in petroleum refinery.

A

Relative volatility of a binary mixture changes appreciably with the minor change in temperature.

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11
Q

Which of the following is not a unit of mass transfer co-efficient ?
None of these

A

None of these

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12
Q

The falling rate period in the drying of a solid is characterised by
increase in rate of drying.
increasing temperatures both on the surface and within the solid.
decreasing temperatures.
none of these.

A

increasing temperatures both on the surface and within the solid.

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13
Q

In which of the following unit operations, the selectivity is an important parameter ?
Distillation
Solvent extraction
Absorption
None of these

A

Solvent extraction

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14
Q

Which of the following is an undesirable characteristic for the solvent used in gas absorption ?
Low vapor pressure
Low viscosity
High gas solubility
None of these

A

None of these

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15
Q

Which of the following equipments is not used for liquid dispersion ?
Wetted wall towers
Packed towers
Venturi scrubbers
Agitated vessels

A

Agitated vessels

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16
Q

Diameter of raschig rings used in packed tower in industry is normally around __________ inches.
2
8
12
18

A

2

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17
Q

The diffusion co-efficient in m2 /s. of acetic acid in benzene (liquid in liquid) is
2.09 x 10-4
2.09 x 10-5
2.09 x 10-9
2.09 x 10-12

A

2.09 x 10-9

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18
Q

Pick out the wrong statement.
The Reynolds analogy for mass transfer is given by Lewis relation and is applicable, when Schmidt number is one.
Sherwood number for flow in pipes can be expressed as the ratio of the concentration gradient at wall to the overall concentration difference.
According to film theory for equimolar counter diffusion, the mass transfer coefficient is given by DAB(b)P - 3, Q - 2
The z-component of the total mass flux of a component A in binary mixture of A and B is given by - Dab’.dCA/dz.

A

According to film theory for equimolar counter diffusion, the mass transfer coefficient is given by DAB(b)P - 3, Q - 2

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19
Q

In case of non-ideal gases and liquids, the molal diffusivity
varies inversely as the pressure.
varies directly as the pressure.
is independent of pressure.
is equal to the volumetric diffusivity.

A

is independent of pressure.

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20
Q

Condensation of a vapour-gas mixture just begins, when (where, p = partial pressure of the vapour P = vapour pressure of the liquid )
p = P
p&raquo_space;P
p < P
p &laquo_space;P

A

p = P

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21
Q

__________ number indicates the ratio of the rates of the heat and mass transfer incase of a cooling tower.
Sherwood
Stanton
Lewis
Peclet

A

Lewis

22
Q

The expression, y(1 - x)/x(1 - y) is for
absorption factor
relative volatility
selectivity
Murphree efficiency

A

relative volatility

23
Q

In physical terms, Schmidt number means
thermal diffusivity/mass diffusivity.
thermal diffusivity/momentum diffusivity.
momentum diffusivity/mass diffusivity.
mass diffusivity/thermal diffusivity.

A

momentum diffusivity/mass diffusivity.

24
Q

In case of liquids, the binary diffusivity is proportional to (where, T = temperature)
T
sqrt T
T^2
1/T

A

T

25
Q

The diffusivity, DAB (for component A diffusing in B) is equal to the diffusivity DBA (for component B diffusing in A) for a binary mixture of
Newtonion liquids
non-Newtonion liquids
ideal gases
real gases

A

ideal gases

26
Q

Mass transfer co-efficient is directly proportional to DAB0.5, according to __________ theory.
penetration
surface renewal
film
none of these

A

penetration

27
Q

Sand is dried in foundaries in a___drier.
rotary
fluidisedbed
vacuum
spray

A

fluidisedbed

28
Q

Which of the following employs an accessory known as ‘drift eliminator’ ?
Multiple effect evaporator.
Mechanical draft cooling tower.
Rotary dryer.
Rotating disc contactor.

A

Mechanical draft cooling tower.

29
Q

Pick out the correct statement.
Higher hold up of the solid in the rotary dryer results in better exposure of the solids to the gas.
The ‘Hatta number’ is important in problems involving gas absorption without chemical reaction.
For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both components is linear in the case of steady state equimolal counter-diffusion.
Total reflux in case of distillation operation requires infinite number of plates for a binary system separation.

A

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

30
Q

Pick out the correct statement.
For identical gas flow rates, less pressure drop occurs through a plate tower than through a packed tower.
Plate column can handle greater liquid loads without flooding than packed column, but the liquid hold up is more in the case of plate column.
For the same duty, plate columns weigh less than packed columns.
all (a), (b) and (c).

A

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

31
Q

Humid volume is the total volume in m3 of 1 kg of
vapour laden gas at 1 atm. and room temperature.
gas plus its accompanying vapour at 1 atm. and room temperature.
gas plus its accompanying vapour at 1 atm. and gas temperature.
vapour laden gas at 1 atm. and gas temperature.

A

gas plus its accompanying vapour at 1 atm. and gas temperature.

32
Q

Diameter to height ratio for a rashig ring is
1
0.5
2
8

A

1

33
Q

The equipment used in the extraction of highly corrosive radio active liquids is
pulse column
spray column
mixer settler
baffle tower

A

pulse column

34
Q

Advantage of continuous drying over batch drying is that the
drying cost per unit weight of dried product is less.
product with more uniform moisture content is produced.
equipment size required is smaller.
all ‘a’, ‘b’ & ‘c’

A

all ‘a’, ‘b’ & ‘c’

35
Q

With increase in temperature, the rate of extraction in leaching (solid-liquid extraction system)
increases
decreases
remains unaffected
increases Linearly

A

increases

36
Q

In a packed bed absorption column, the channelling will be noted by the
increase in flow rate.
sharp drop in pressure drop.
sharp rise in pressure drop.
none of these.

A

sharp drop in pressure drop.

37
Q

Gaseous diffusivity at atmospheric pressure is of the order of __________ cm2/second.
1
1 to 5
5 to 10
> 10

A

1

38
Q

In liquid-liquid extraction, the number of phases at plait point is
1
2
3
4

A

1

39
Q

In a liquid-liquid extraction, 10 kg of a solution containing 2 kg of solute C and 8 kg of solvent A is brought into contact with 10 kg of solvent B. Solvent A and B are completely immiscible in each other whereas solute C is soluble in both the solvents. The extraction process attains equilibrium. The equilibrium relationship between the two phases is Y* = 0.9X, where Y* is the kg of C/kg of B and X is kg of C/kg of A. Choose the correct answer.
The entire amount of C is transferred to solvent B.
Less than 2 kg but more than 1 kg of C is transferred to solvent B.
Less than 1 kg of C is transferred to B.
No amount of C is tranferred to B.

A

The entire amount of C is transferred to solvent B.

40
Q

The surface renewal frequency in Danckwerts’ model of mass transfer is given by (KL: mass transfer co-efficient)
sqrt (KL^2 * DA)
KL^2 * DA
KL^2 / DA
KL / DA^2

A

sqrt (KL^2 * DA)

41
Q

If Rm is the minimum reflux ratio, the optimum reflux ratio may be around __________ Rm.
1.2 to 1.5
2.5 to 3
3 to 4
5

A

1.2 to 1.5

42
Q

During dehumidification of unsaturated air wet bulb temperature & partial pressure of vapor are not constant. However, during evaporative cooling process with recirculated water supply, the __________ remains constant.
wet bulb temperature
partial pressure of water vapor
relative humidity
none of these

A

wet bulb temperature

43
Q

In case of absorption, both the operating and equilibrium lines will be straight for
isothermal operation.
dilute solutions.
dilute solutions and isothermal operation.
none of these.

A

dilute solutions and isothermal operation.

44
Q

Mass transfer co-efficient varies as DAB0.5, according to the __________ theory.
film
surface renewal
penetration
none of these

A

surface renewal

45
Q

For an absorber, both equilibrium and operating line will be straight for
concentrated solution and non-isothermal operation.
dilute solution and non-isothermal operation.
dilute solution and isothermal operation.
concentrated solution and isothermal operation.

A

dilute solution and isothermal operation.

46
Q

A distillation column separates 10000 kg/hr of a benzene-toluene mixture as shown in the figure below :In the figure xF, xD and xW represent the weight fraction of benzene in the feed, distillate and residue respectively. The reflux ratio is
0.5
0.6
1.0
2.0

A

0.6

47
Q

Unsaturated air (with dry bulb and wet bulb temperatures being 45°C and 25°C respectively) is passed through a water spray chamber maintained at 23°C. The air will be cooled and
humidified with wet bulb temperature decreasing.
humidified at constant wet bulb temperature.
dehumidified.
none of these

A

humidified with wet bulb temperature decreasing.

48
Q

Humid volume, at a given temperature is a/an __________ function of humidity.
inverse
exponential
linear
logarithmic

A

linear

49
Q

The Schmidt number which is defined as, μ/ρ D, is the ratio of the
momentum diffusivity to the mass dif-fusivity.
thermal diffusivity to the mass diffusivity.
momentum diffusivity to the thermal diffusivity.
none of these.

A

momentum diffusivity to the mass dif-fusivity.

50
Q

If f is defined as above, then which of the following applies to a feed at dew point ?
f = 1
f < 1
f > 1
0 < f < 1

A

f = 1

Philippine Chemical Engineering Licensure Examination Day 2 Separation Processes (14 decks)

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