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Chemical Engineering
Mass Transfer
Quiz 6
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Q.1
The vapour pressure exerted by the moisture contained in a wet solid depends upon the
Nature of the moisture
Temperature
Nature of the solid
All of the above
Q.2
McCabe-Thiele method
Uses molal units for material and energy balance
Uses weight fractions to express liquid and vapour composition
Can use any type of units
Is more accurate than Ponchan-Savarit method
Q.3
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
Q.4
Pick out the wrong statement
A horizontal line on the humidity chart indicates the temperature changes at constant molal humidity
When water is cooled from 80 to 70°C by exposure to the air with a wet bulb temperature of 60°C, then both the approach & the range would be 10°C
For unsaturated air-water vapor mixture at atmospheric conditions, the wet bulb temperature & adiabatic cooling lines are the same
Relative saturation of unsaturated mixture of water vapor & air can not be increased by either reducing the mixture temperature or by increasing the total pressure
Q.5
Pick out the wrong statement.
Packed towers are preferred for vacuum operation, because the pressure drop through the packing is less and they (packings) also lessen the possibility of tower wall collapse
Packed towers are preferred over plate towers for handling corrosive and foamy liquids
Diameter of randomly packed tower is normally more than 1.2 metres
Due to uneven supply and improper distribution of liquid, problem of channeling, loading & flooding is generally encountered in packed towers
Q.6
Water-ethyl alcohal solution can be concentrated (in respect of alcohal concentration) by __________ distillation.
Atmospheric
Vacuum
High pressure
None of these
Q.7
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
Q.8
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
Q.9
Molecular distillation is
High temperature distillation
For heat-sensitive materials
Very low pressure distillation
Both B and C
Q.10
Pick out the wrong statement.
When the concentration difference for the mass transfer becomes zero at the bottom of the gas absorption tower, then the upper end of the operating line touches the equilibrium curve
The average distance between the operating line and equilibrium line is large, when the liquid-gas ratio is also large in case of a counter current gas absorption tower
The operating line lies above the equilibrium curve in case of a gas desorber
With decrease in the liquid flow rate for a fixed gas flow rate, the slope of the operating line decreases, in case of gas absorption process
Q.11
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
Q.12
(N
Sh
/N
Re
.N
Sc
) is termed in mass transfer operation as the
Stanton number
Peclet number
Thermal diffusivity
Momentum diffusivity
Q.13
Which one of the following devices is not used for both the absorption as well as the liquid-liquid extraction processes?
Packed towers
Plate towers
Spray towers
Wetted wall columns
Q.14
The apex of an equilateral-triangular coordinate (in ternary liquid system) represents a/an
Pure component
Binary mixture
Ternary mixture
Insoluble binary system
Q.15
1 kg of a saturated aqueous solution of a highly soluble component A at 60°C is cooled to 25°C. The solubility limits of A are (0.6 kgA/kg water) at 60°C and (0.2 kgA/kg water) at 25°C. The amount in kg of the crystals formed is
0.4
0.25
0.2
0.175
Q.16
Molecular seives are porous
Alumina
Silica
Synthetic zeolites crystals/metal alumino-silicates
None of these
Q.17
The velocity, concentration and temperature boundary, for the boundary layer development on a flat plate during connective mass transfer will be same, if
N
Sc
= 1
N
Sc
= N
Pr
= N
Le
N
Pr
= N
Le
N
Sc
= N
Le
Q.18
Lewis number, which is important in problems involving simultaneous heat and mass transfer, is the ratio of
Mass diffusivity to momentum diffusivity
Thermal diffusivity to mass diffusivity
Momentum diffusivity to thermal diffusivity
None of these
Q.19
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
Q.20
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
Q.21
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
Q.22
'ADDUCTS' and 'CLATHRATES' are used in case of
Extractive distillation
Crystallisation
Absorption
None of these
Q.23
Azeotropic distillation is employed to separate
Constant boiling mixture
High boiling mixture
Mixture with very high relative volatility
Heat sensitive materials
Q.24
In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the molality is
0.50
0.60
2
1
Q.25
L/mG is the expression for
Absorption factor
Brinkman number
Slope of operating line in absorber
Slope of operating line in stripper
Q.26
Molecular diffusion is caused by the
Transfer of molecules from low concentration to high concentration region
Thermal energy of the molecules
Activation energy of the molecules
Potential energy of the molecules
Q.27
The McCabe Δ L law states that the
Molar heats of vaporisation of components are nearly equal
Linear crystal growth rate depends on the degree of supersaturation
Linear crystal growth rate does not depend on the crystal size
Linear crystal growth rate depends on the crystal size
Q.28
The efficiency of a plate column will be maximum, when the flow is ideal __________ the plate.
Across
Above
Both A & B
Neither A nor B
Q.29
Boiling point diagram is not affected by the ambient
Pressure
Humidity
Temperature
Both B and C
Q.30
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
Q.31
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
Vapour pressure of component A to that of component B
Vapour pressure of component A to the total pressure
Vapour pressure of component A to the partial pressure of A
Partial pressure of component A to the total pressure
Q.32
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
Q.33
With increase in temperature, the leaching rate increases due to
Decreased liquid viscosity
Increased diffusivity
Both A & B
Neither A nor B
Q.34
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
Q.35
Lewis number (Le) is
Sc x Pr
Pr x St
Sh x Pr
St x Sh
Q.36
Pore size of the molecular seive 5A is __________ mm.
5
0.5
0.05
50
Q.37
Pick out the wrong statement.
The operating line always lies above the equilibrium solubility curve in case of a single component absorber
The operating line always lies below the equilibrium solubility curve in case of a single component stripper
The operating pressure in solvent extraction system should be below vapor pressures of all components
The solubility of a particular gas in ideal solution in any solvent is always the same
Q.38
Diffusion co-efficient generally depends upon the temperature, pressure & the nature of the components of the system. Its dimension is not the same as that of the
Mass transfer co-efficient
Thermal diffusivity
Kinematic viscosity
Volumetric diffusivity
Q.39
For which of the following unit operations, Lewis number is of significance?
Adsorption
Binary distillation
Gas absorption
Humidification
Q.40
Desulphurisation of petrol is done in a
Bollman extractor
Rotating disc extractor
Packed extraction column
Plate type extraction column
Q.41
Occurrence of 'case hardening' during drying of a high moisture solid cake __________ the drying rate.
Increases
Decreases
Does not affect
Exponentially increases
Q.42
Dorr thickener is an equipment used for
Classification
Sedimentation
Clarification
Leaching
Q.43
Which is the controlling factor for a drum drier?
Diffusion
Heat transfer
Both A & B
Neither A nor B
Q.44
Absorption factor is defined as (where, S₁ = slope of the operating line S₂ = slope of the equilibrium curve)
S₂/S₁
S₁/S₂
S₁ - S₂
S₁ x S₂
Q.45
Pick out the wrong statement.
In solvent extraction, the distribution co-efficient should be as large as possible for solvent economy
With increase in pressure, the solubility of gases in solvent increases at a fixed temperature
Decrease in Murphree plate efficiency is an indication of entrainment in distillation coloumn
The capacity of a distillation coloumn is maximum at total reflux
Q.46
In case of gases, the binary diffusivity is proportional to (where, P = pressure)
P
1/P
1/√P
√P
Q.47
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 of the above
Q.48
Separation of two volatile liquids by distillation makes use of their
Selectivity
Relative volatility
Solubility
Density difference
Q.49
The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by
Raising the temperature
Lowering the total pressure
Both A & B
Neither A nor B
Q.50
__________ columns are used for liquid dispersion in a continuous gas phase.
Packed
Pulse
Bubble cap
Sieve plate
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