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Chemical Engineering
Mass Transfer
Quiz 4
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Q.1
Dry bulb temperature of the gas is __________ the wet bulb temperature.
Less than
More than
Equal to
None of these
Q.2
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 of the above
Q.3
A mixture of 10% C₆H₆ vapour in air at 25°C and 750 mm Hg has a dew point of 20°C. Its dew point at 30°C and 700 mm Hg will be around __________ °C.
21.7
20
27.3
18.7
Q.4
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
Q.5
In continuous distillation, the internal reflux ratio (R
i
) and the external reflux ratio (R
e
) are related as
R
i
= R
e
/(1 - R
e
)
R
i
= (1 - R
e
)/R
e
R
i
= R
e
R
i
= R
e
/(1 + R
e
)
Q.6
At a fixed total pressure, humidity depends only on the
Partial pressure of vapour in the mixture
Heat capacity of the vapour
Density of the vapour
None of these
Q.7
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
Q.8
Though, theoretically the adsorption & desorption isotherms is expected to coincide but sometimes at least a part of the isotherms does not coincide and this phenomenon is known as adsorption hysterisis. In such cases, the desorption equilibrium pressure is __________ that obtained for adsorption.
Lower than
Higher than
Same as
Either same or higher than
Q.9
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
Q.10
Which of the following is not fixed by the process requirements, in the design of absorbers?
Flow rate of the entering gas
Composition of the entering liquid
Terminal concentrations of gas stream
None of these
Q.11
For continuous drying of grannular or crystalline material, the dryer used is the __________ dryer.
Tunnel
Tray
Rotary
None of these
Q.12
Which of the following is the most suitable for extraction in a system having very low density difference?
Mixer-settler extractor
Centrifugal extractor
Pulsed extractor
Packed extraction tower
Q.13
Pick out the correct statement.
Diffusivity decreases with increase in temperature
Diffusivity increases with increase in molecular weight
Diffusivity increases with the size of the individual molecule
None of these
Q.14
The rate of solid-liquid extraction is limited by the
Phase change of the solute as it dissolves in the solvent
Diffusion of the solute through the solvent in the pores to the outside of the particle
Diffusion of the solute from the solution in contact with the particle to the main bulk of the solution
All of the above
Q.15
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
Q.16
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
Q.17
The cooling effect in a cooling tower can not be increased by
Increasing the air velocity over the wet surfaces
Reducing the humidity of entering air
Lowering the barometric pressure
None of these
Q.18
The most efficient cooling tower out of the following is
Induced draft
Forced draft
Natural draft
Atmospheric
Q.19
The relative volatility of a binary mixture at the azeotropic composition is
1
> 1
0
∞
Q.20
Packed column distillation is limited to the column __________ metres.
Height < 6
Diameter < 0.6
Both A & B
Neither A nor B
Q.21
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 √D
Dependent on the Reynolds number
Q.22
Which of the following processes is followed by unsaturated air (with dry bulb temperature 12°C and relative humidity 47%) passing through water spray washer (temperature of water being constant at 40°C?
Humidification only
Heating only
Both heating and humidification
Evaporative cooling
Q.23
Cox chart is useful in the design of
Distillation column
Evaporator
Dryer
Crystalliser
Q.24
An air-water vapour mixture has a dry bulb temperature of 60°C and a dew point temperature of 40°C. The total pressure is 101.3 kPa and the vapour pressure of water at 40°C and 60°C are 7.30 kPa and 19.91 kPa respectively.The humidity of air sample expressed as kg of water vapour/kg of dry air is
0.048
0.079
0.122
0.152
Q.25
The binary diffusivity in gases and liquids vary respectively as
T
3/2
and T
T and T
3/2
√T and T
3/2
T
3/2
and √T
Q.26
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
Decoction
Percolation
Elutriation or elution
None of these
Q.27
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
Q.28
Weight of 1 m³ of humid air as compared to 1 m³ of dry air, under the same conditions, is
Less
More
Same
Unpredictable
Q.29
Critical humidity of a solid salt means the humidity
Above which it will always become damp
Below which it will always stay dry
Both A and B
Above Which it will always become dry and below which it will always stay damp
Q.30
The process employing desorption of the absorbed solute by a solvent is called
Elution
Osmosis
Reverse osmosis
Sublimation
Q.31
Degree of freedom for leaching and solvent extraction process is
1
3
0
2
Q.32
Inside the distillation columns, the
Highest temperatures is near the feed plate
Driving force for the liquid flow is its weight
Vapors are not always at their dew points
All of the above
Q.33
If moisture content of solid on dry basis is X, then the same on wet basis is
X/(X + 1)
X/(X - 1)
(X + 1)/X
(X - 1)/X
Q.34
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
Q.35
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
Q.36
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
Q.37
The reciprocal of stripping factor is termed as
Selectivity index
Relative volatility
Absorption factor
Murphree efficiency
Q.38
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
Q.39
A slurry is to be dried to produce flaky solid. Which dryer would you recommend?
Spray dryer
Drum dryer
Rotary dryer
Dielectric dryer
Q.40
Channelling is most severe
In towers packed with stacked packing
In towers packed randomly with crushed solids
In dumped packing of regular units
At very high liquid flow rate
Q.41
According to Poiseuille's law, the permeability for gas flow through a capillary is proportional to (where, μ = gas viscosity)
μ
1/μ
√μ
μ²
Q.42
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
Higher dew point
Higher absolute (specific) humidity
Higher relative humidity
Higher wet bulb temperature
Q.43
Absorption accompanied by heat evolution results in
Increased capacity of the absorber
Increase in equilibrium solubility
Decrease in equilibrium solubility
None of these
Q.44
Molecular seives are regenerated by heating to __________ °C.
< 150
200-330
> 500
> 1000
Q.45
If a two phase system is in physical equilibrium; then it means that, the
Escaping tendency of each component from the liquid phase to the vapor phase is exactly equal to that from vapor phase to liquid phase
Temperature of the liquid phase is equal to that of the vapor phase
Total pressure throughout the liquid phase is equal to that throughout the vapor phase
All of the above
Q.46
Mass transfer co-efficient is directly proportional to D
AB
0.5
, according to __________ theory.
Penetration
Surface renewal
Film
None of these
Q.47
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
Q.48
CO₂ can be absorbed by
Hot cupric oxide
Heated charcoal
Cold Ca(OH)₂
Alumina
Q.49
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
Q.50
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
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