Mass Transfer (Set 5) Flashcards
As one of the transport phenomena, the concepts in mass transfer are crucial for design, operation, and maintenance of mass or heat & mass transfer equipment such as mixing and separation processes.
Which of the following parameters remains constant during chemical dehumidification?
Dry bulb temperature
Drying of a solid involves ____ transfer.
both heat and mass
Mechanism of moisture removal in case of freeze drying of food stuff is by
sublimation
The dew point of an unsaturated gas-vapor mixture does not depend upon the ____ of the mixture.
temperature
Which is not concerned directly with mass transfer?
Froude number
Removal of ____ exemplifies an adsorption unit operation.
water from petrol
Can the efficiency of a plate in the distillation tower be greater than 100%?
Never
With increase in the mass velocity of the gas, the rate of drying during the constant rate period ____ , if the conduction and radiation through the solid are negligible.
increases
For gas absorption, low viscosity solvents are preferred, because of their
all (a), (b) and (c).
To remove all the moisture from a wet solid it requires exposure to ____ air.
perfectly dry
The operating cost of a distillation column at minimum reflux ratio is
minimum
The reflux to a distillation column is 100 moles/hr, when the overhead product rate is 50 moles/hr. The reflux ratio is
2
Molecular diffusivity of a liquid
increases with temperature.
The wet and ‘dry bulb temperature for a vapour-gas mixture are 25°C and 30°C respectively. If the mixture is heated to 45°C at constant pressure, the wet bulb temperature will be ____ °C.
> 25
Henry’s law states that the
partial pressure of a component over a solution is proportional to its mole fraction in the liquid.
Ammonia present in the coke oven gas is removed by washing with
dilute ammoniacal liquor
With increase in temperature, the leaching rate increases due to
both (a) and (b)
Which of the following processes is not an example of adsorption applied to gaseous separations?
Decolouration of yellow glycerene.
The critical moisture content in case of drying indicates the ____ rate period.
beginning of falling
Pick out the wrong statement
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.
According to Poiseuille’s law, the permeability for gas flow through a capillary is proportional to (where, μ = gas viscosity)
1/μ
For a binary mixture distillation process, the degree of freedom is 2. However, if the pressure is fixed in this process, the number of independent variables in this process will be
1
H2S is being absorbed in a gas absorber unit. The height of the transfer unit based on the overall mass transfer coefficient on the gas side is 0.4 m. The equilibrium data is given by, y = 1.5 x. The bulk concentration of H2S has to be reduced from 0.05 to 0.001 mole fraction in the gas side. The height of the tower (in metres) corresponding to an operating line given by, y = 5x + 0.001 is
2
Packed column distillation is limited to the column ____ metres.
both (a) & (b)
For the flow of gases through a capillary, with increase in temperature, the permeability ____ as per Knudsen law.
increases
Which of the following is directly concerned with psychrometry?
Lewis relationship
Plate efficiency in a distillation column is reduced due to the ____ of liquid.
all (a), (b) & (c)
The most efficient cooling tower out of the following is
induced draft
Sodium bicarbonate is produced during soda ash manufacture using a ____ tower.
baffle
Powdery materials can be guarded against caking tendency on storage by
none of these.
In case of cooling towers, the ratio of the rates of heat and mass transfer is indicated by the ____ number.
Lewis
Which one of the following devices is not used for both the absorption as well as the liquid-liquid extraction processes?
Wetted wall columns
The temperature of water cooled in cooling tower is always ____ temperature of entering air.
more than the wet bulb
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?
Both heating and humidification
Mass transfer co-efficient is directly proportional to DAB according to the ____ theory.
film
The relative volatility of a binary mixture at constant temperature ____ the total pressure.
decreases with increase in
Tower diameter may be decreased by
use of increased tray spacing.
Rayleigh’s equation applies to ____ distillation.
differential
Steady state equimolal counter diffusion is encountered in
separation of a binary mixture by distillation.
Which of the following is considered equivalent to one theoretical stage in Mc-Cabe Thiele’s method?
Both (b) and (c)
Polar organic compounds are normally used as separating agents for the azeotropic and extractive distillation. Which of the following is the most important factor to be considered for the choice of the separating agent for extractive distillation?
Selectivity
As the reflux ratio increases, the slope of the operating line for rectifying section
increases
Cox chart, which is useful in the design of distillation column particularly for petroleum hydrocarbons, is a plot of (where, P = vapor pressure, T = temperature)
log P vs . T
The unit of volumetric diffusivity is
cm2/sec
For a ternery mixture, in which equilateral triangular co-ordinate is used in leaching and extraction, a ____ of the equilateral triangular co-ordinates.
pure component is represented by the apex.
Steady state temperature reached by a small amount of liquid evaporating into a large amount of unsaturated vapour-gas mixture is called the ____ temperature.
wet-bulb
The Reynolds number of the liquid was increased 100 fold for a laminar falling film used for gas-liquid contacting. Assuming penetrating theory is applicable, the fold increase in the mass transfer co-efficient (Kc) for the same sytem is
10
The slope of 9-line is determined by the
thermal condition of the feed
In steam distillation, the
product must be immiscible with water.
Which of the following can be calculated theoretically using steam table and Dalton’s law of partial pressure; if the relative humidity and dry bulb temperature of moist air is known?
Wet bulb temperature
Steam distillation is used for separation of high boiling
both (a) and (b).
The feed to fractionating column is changed from saturated vapour to saturated liquid. If the separation and reflux ratio remains unchanged, the number of ideal stages will
increase
Rose oil is extracted from rose leaves using ____ distillation.
steam
Hypersorption refers to a ____ process.
moving bed adsorption
Which of the following is the correct ternery diagram for liquid-liquid extraction system comprising of two pairs partly soluble (e.g., chlorobenzene-water-methyl ethyl ketone system)?
https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/317-500-1.png
Extraction of coffee from its seed is done by
leaching.
In azeotropic mixture, the equilibrium vapour composition is
same as liquid composition.
With lapse of time, the overhead composition of light component in case of batch distillation with constant reflux
decreases
Lewis number, which is important in problems involving simultaneous heat and mass transfer, is the ratio of
thermal diffusivity to mass diffusivity.
According to the film theory of mass transfer, the mass transfer co-efficient is proportional to (where, D = molecular diffusivity)
D
Dry bulb temperature of the gas is ____ the wet bulb temperature.
more than
Decoction refers to the use of solvent
at its boiling point
Flash distillation is suitable for separating the constituents of a binary system, which
have very wide boiling points.
The ratio of Murphree plate efficiency to point efficiency is 1 in a ____ flow model.
perfectly mixed
The rough value of diffusion co-efficient of water vapor into air at 25°C may be about ____ cm2/sec.
0.25
Flooding in a column results due to
high pressure drop
Which of the following gas-liquid contacting devices incurs the least pressure drop for a particular duty?
Wetted wall tower
A liquid mixture contains 30% o-xylene, 60% p-xylene and 10%. m-xylene (all percentages in w/w). Which of the following statements would be true in respect of this mixture?
The mixture exhibits an azeotrope at 101.3 kPa.
Unsaturated air (with dry bulb temperature and dew point being 35°C and 18°C respectively) is passed through a water spray chamber maintained at 15°C. The air will be cooled
and dehumidified with decrease in wet bulb temperature.
The process employing desorption of the absorbed solute by a solvent is called
elution
If the overall efficiency and Murphree plate efficiency are equal, then both the equilibrium and operating lines are
both (a) & (b)
Which of the following operations does not involve leaching?
Removing nicotine from its water solution by kerosene.
The recovery of pencillin from the acidified fermentation broth is done by
liquid extraction
Unit operation involved in the prilling of urea is
both (b) and (c)
Molecular seives are porous
synthetic zeolites crystals/metal alumino-silicates.
Calcium ammonium nitrate (a fertiliser) is dried in a ____ dryer.
rotary
A binary mixture of benzene and cyclohexane is separated by
extractive distillation
Component A is diffusing in a medium B. The flux NA relative to a stationary point is equal to the flux due to molecular difusion, if
there is equimolar counter diffusion.
Cox chart is useful in the design of
distillation column
Dew point of an air-water vapor mixture
all ‘a’, ‘b’ & ‘c’.
Can a cooling tower cool water below the wet bulb temperature of inlet air?
no
The solvent used in liquid-liquid extraction should have ____ less than one.
neither (a) nor (b).
The suitable evaporator for concentration of foaming liquids is a ____ evaporator.
long tube
The ratio of Murphree plate efficiency to point efficiency is always > 1 in a ____ flow model.
plug
Tea percolation employs
leaching
Which of the following assumes constant molal vaporisation and overflow?
McCabe-Thiele method
Absorption factor, for a fixed degree of absorption from a fixed amount of gas should be
> 1
Selectivity of the solvent used in solvent extraction should be
> 1
Pick out the wrong statement pertaining to leaching.
Fine solids can not be leached in a Pachuka tank.
Wet bulb and dry bulb temperatures becomes identical at ____ percent saturation curve.
100
NSc/NPr is called the
Lewis number
McCabe-Thiele method
uses molal units for material and energy balance.
The film penetration model of mass transfer was enunciated by
Toor and Marchello
The most economical range of absorption factor is
1.25 to 2
Channelling is most severe
in towers packed with stacked packing.
Out of two equilibrium curves, first one lies above the diagonal and the second lies below the diagonal in the x-y plot. It means that separation by distillation is
more readily done in the second case compared to first one.
ADDUCTS’ and ‘CLATHRATES’ are used in case of
crystallisation.
Adsorption is an unit operation which generally involves ____ systems.
fluid-solid
In case of ____ distillation, a solvent is added to alter the relative volatility of the mixture to be separated.
extractive
Separation of the isotopes of helium for scientific investigations is done by
thermal diffusion
