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Chemical Engineering Reviewer > Heat Transfer (Set 1) > Flashcards

Heat Transfer (Set 1) Flashcards

As one of the transport phenomena, the concepts in heat transfer are crucial for design, operation, and maintenance of heat transfer equipment such as heat exchangers and insulation.

1
Q

Crystal size in a continuous crystalliser depends upon the

A

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

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2
Q

In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the molality is

A

0.5

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3
Q

Fenske equation determines the

A

minimum number of theoretical plates.

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4
Q

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

A

hot water entering the tower and the cooled water leaving the tower.

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5
Q

Which of the following is the most suitable for extraction in a system having very low density difference?

A

Centrifugal extractor

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6
Q

Total reflux in a distillation operation requires minimum

A

number of plates

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7
Q

The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by
a. raising the temperature.
b. lowering the total pressure.

A

both (a) and (b).

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8
Q

The difference of wet bulb temperature and adiabatic saturation temperature of unsaturated mixture of any system is

A

(+)ve

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9
Q

Fenske’s equation for determining the minimum number of theoretical stages in distillation column holds good, when the

A

relative volatility is reasonably constant.

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10
Q

When the temperature and humidity of air is low, we usually use ____ draft cooling tower.

A

natural

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11
Q

Pick out the correct statement.

A

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

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12
Q

____ columns are used for liquid dispersion in a continuous gas phase.

A

Packed

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13
Q

Overall efficiency of the distillation column is

A

the ratio of number of ideal plates to actual plates.

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14
Q

On addition of solute in the solvent, the ____ of the solution decreases.

A

both (b) and (c)

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15
Q

Which is the controlling factor for a drum drier?

A

Heat transfer

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16
Q

Drying operation under vacuum is carried out to

A

reduce drying temperature.

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17
Q

Air initially at 101. 3 kPa and 40°C and with a relative humidity of 50%, is cooled at constant pressure to 30°C. The cooled air has a

A

higher relative humidity

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18
Q

Separation of two or more components of a liquid solution can not be achieved by

A

absorption

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19
Q

Stefan’s law describes the mass transfer by

A

both ‘a’ & ‘b’

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20
Q

At minimum reflux ratio for a given separation

A

number of plates is infinity.

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21
Q

Relative humidity is the ratio of the

A

partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.

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22
Q

In batch distillation with constant reflux, overhead product composition ____ with time.

A

decreases

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23
Q

Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the ____ of a fibre.

A

electrical resistance

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24
Q

Heat in BTU necessary to increase the temperature of 1 lb of gas and its accompanying vapour by 1°F is called the

A

specific heat

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25
Q

To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)

A

increase ‘S’ and decrease ‘G’.

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26
Q

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

A

1

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27
Q

Dew point of a gas-vapour mixture

A

decreases with decrease in pressure.

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28
Q

In a packed absorption tower, if the equilibrium and operating lines are both straight lines, then the ratio, HETP/HTUOG ____ the absorption factor.

A

both (a) and (b)

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29
Q

Which of the following plays an important role in problems of simultaneous heat and mass transfer?

A

Lewis number

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30
Q

In case of an absorber, the operating

A

line always lies above the equilibrium curve.

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31
Q

As the reflux ratio in a distillation coloumn is increased from the minimum, the

A

total cost first decreases and then increases.

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32
Q

Absorption factor is defined as (where, S1 = slope of the operating line S2 = slope of the equilibrium curve)

A

S1/S2

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33
Q

A plait point is the point on the solubility curve, where the tie line reduces to a point. What is the number of plait point for a ternery system containing twopairs of partially miscible liquids?

A

0

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34
Q

Which of the following remains constant during sensible cooling process?

A

Both (a) and (b)

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35
Q

Physical absorption is

A

both (b) and (c)

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36
Q

Make up water is required in a cooling tower to replace the water lost by

A

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

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37
Q

Which of the following quantities need not be fixed before starting the design of a co-current absorber?

A

Flow rate of entering liquid

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38
Q

Mass transfer co-efficient of liquid is

A

affected more by temperature than that for gases.

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39
Q

Absorption accompanied with chemical reaction is exemplified by the absorption of

A

SO2 in alkaline solution.

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40
Q

Which of the following unit operations makes use of Thiele-Geddes equation?

A

Multicomponent distillation.

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41
Q

Which of the following liquid-vapor contacting devices provides maximum contact surface area for a particular duty?

A

Wetted wall column

42
Q

The equipment frequently used for adiabatic humidification-cooling operation with recirculating liquid is

A

spray chamber

43
Q

Chemisorption (chemical adsorption) is

A

an irreversible phenomenon.

44
Q

The rate of solid-liquid extraction is limited by the

A

all ‘a’, ‘b’ & ‘c’.

45
Q

Raoult’s law applies to the

A

solvents.

46
Q

In distillation columns, the number of bubble caps per tray primarily depends upon the

A

allowable gas and liquid velocities.

47
Q

In distillation, overhead product contains

A

any number of components

48
Q

With increase in pressure, the relative volatility for a binary system

A

decreases.

49
Q

Low viscosity absorbent is preferred for reasons of

A

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

50
Q

Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as

A

K ∝ D

51
Q

The McCabe Δ L law states that the

A

linear crystal growth rate does not depend on the crystal size.

52
Q

Bollman extractor

A

is used for extraction of oil from oilseed.

53
Q

The relation, Sc = Pr = 1, is valid, when the mechanism of ____ ansfer is same.

A

heat and mass

54
Q

A coalescer in a mixer-settler liquid-liquid extraction coloumn

A

all ‘a’, ‘b’, & ‘c’.

55
Q

For the same feed, feed quality and separation (in a distillation column), with the increase of total pressure, the number of ideal plates will

A

increase

56
Q

Pick out the correct statement.

A

Ponchan-Savarit method is more accurate than McCabe-Thiele method to determine the number of theoretical stages required for the separation of non-ideal binary system by distillation.

57
Q

When the liquid phase and vapour phase of a binary system obeys Raoult’s and Dalton’s law respectively, the relative volatility is the ratio of

A

vapour pressure of component A to that of component B.

58
Q

The operation involved when the soluble material is largely on the surface of an insoluble solid and is merely washed off by the solvent is called

A

elutriation or elution

59
Q

In the constant rate period of the rate of drying curve for batch drying,

A

surface evaporation of unbound moisture occurs.

60
Q

It takes 6 hours to dry a wet solid from 50% moisture content to the critical moisture content of 15%. How much longer it will take to dry the solid to 10% moisture content, under the same drying conditions? (The equilibrium moisture content of the solid is 5%).

A

71 min

61
Q

Agitator is provided in a crystalliser for

A

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

62
Q

____ diffusion is used for separating the isotopes of methane.

A

Thermal

63
Q

Ordinary diffusion process is also called ____ diffusion.

A

concentration

64
Q

Pick out the wrong statement.

A

Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column.

65
Q

Pick out the wrong statement pertaining to the rotary dryer.

A

Rotary dryer is suitable for drying sticky material.

66
Q

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

A

low pressure drop and low hold up.

67
Q

If the path of liquid across the plate is very long as in case of large diameter tower, Murphree efficiency can be ____ percent.

A

> 100

68
Q

Compound A is extracted from a solution of A + B into a pure solvent S. A Co-current unit is used for the liquid-liquid extraction. The inlet rate of the solution containing A is 200 moles of B/hr.m2 and the solvent flow, rate is 400 moles of S/m2. hr. The equilibrium data is represented by Y = 3X2 , where Y is in moles of a A/moles of B and X is in moles A/moles of S. The maximum percentage extraction achieved in the unit is

A

0.5

69
Q

Raoult’s law is applicable to the

A

ideal solutions

70
Q

Weeping in a distillation column

A

results due to very low gas velocity.

71
Q

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

A

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

72
Q

Wetted wall tower experiment determines the

A

mass transfer co-efficient.

73
Q

In McCabe-Thiele method, at infinite reflux ratio

A

the overhead product is minimum.

74
Q

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

A

increases

75
Q

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

A

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

76
Q

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

A

same

77
Q

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

A

wetted wall

78
Q

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

A

ethyl alcohol-water

79
Q

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

A

rotary

80
Q

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

A

linearly

81
Q

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

A

Sherwood

82
Q

If the specific heats of a gas and a vapor are 0.2KJ/Kg.°K and 1.5 KJ/Kg.°K respectively, and the humidity is 0.01; the humid heat in KJ/°Kg. is

A

0.215

83
Q

Liquid diffusivity is of the order of ____ cm2 /second.

A

10-5 to 10-6

84
Q

The solvent used in liquid extraction should not have high latent heat of vaporisation, because

A

its recovery cost by distillation may be prohibitatively high.

85
Q

At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid ____ that in dry packed tower.

A

is greater than

86
Q

Molarity is defined as the number of gm moles of solute per ____ of solvent.

A

liter

87
Q

The value of Lewis number (Le = Sc/Pr) for air-water vapour system is around

A

1

88
Q

Which of the following T-H diagram is valid for dehumidification operation?

A

https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/317-501-1.png

89
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)

A

less number of trays are required.

90
Q

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

A

exponential

91
Q

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

A

Water-hydrochloric acid.

92
Q

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

A

Peclet

93
Q

The binary diffusivity in gases and liquids vary respectively as

A

T^3/2 and T

94
Q

Pick out the correct statement.

A

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

95
Q

Pick out the correct statement.

A

Electrodylsis is used in the manufacture of NaOH.

96
Q

Pick out the correct statement.

A

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

97
Q

Very tall packed towers are divided into series of beds to

A

avoid channelling

98
Q

Moisture contained by a substance in excess of the equilibrium moisture is called the ____ moisture.

A

free

99
Q

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

A

decreases

100
Q

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

A

steam jet ejector with a barometric condenser

Chemical Engineering Reviewer (42 decks)

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