Mass Transfer (Set 7) 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.
In a gas-liquid absorption coloumn, for obtaining the maximum absorption efficiency
both gas as well as liquid streams should be distributed uniformly.
Reverse osmosis is also called
ultrafiltration.
Which of the following is not a batch drier?
Fluidised bed drier
Steam distillation is not recommended to be used, if the
azeotropic mixture is to be separated and the final product is miscible with water.
Rayleigh equation applies to ____ distillation.
differential
Mass transfer co-efficient ‘K’ according to penetration theory varies with mass dif-fusivity as
D^0.5
Most important factor to be considered in the selection of packings for absorbers is the ____ of packing.
porosity
____ is the separation technique used for desalination of sea water.
Reverse osmosis
The relative saturation of a partially saturated mixture of vapour and gas can be increased by ____ of the mixture.
both (b) and (c)
Danckwerts developed the ____ theory.
surface renewal
Molecular distillation is
both (b) and (c)
Drying of a wet solid under constant drying conditions means the exposure of the wet solid to the air of constant
all (a), (b) & (c)
Which of the following provides maximum contact surface for a liquid-vapour system?
Packed tower
For experimental determination of mass transfer co-efficient by wetted wall tower, the mass transfer area is
known
In stripping section of continuous distillation column, the
liquid is enriched with high boiler.
Molality is defined as the number of gm moles of solute per ____ of solvent.
Kg
____ is concerned with the adsorption equilibria.
Freundlich equation
Which of the following is the correct ternery diagram for liquid-liquid extraction system comprising of one pair partly soluble (e.g. water-benzene-acetic acid in which A-diluent, B - solvent and C - solute)?
https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/317-498-1.png
Fractional solvent extraction
employs two solvents
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.
Raschig ring made of procelain cannot be used for treating concentrated
alkalis
H2S present in naphtha reformed gas is removed by absorbing with
ethanolamine
During constant rate drying period, vaporisation rate per unit drying surface area
does not change with time,
Pick out the wrong statement.
Mass transfer co-efficient does not account for gase-liquid diffusion.
In rectifying section of a continuous distillation column, the
vapour is enriched with high boilers.
For a fixed number of ideal stages in a distillation column, as the reflux ratio is increased, the difference in composition between the top and bottom product streams
increases
According to Chilton-Colburn analogy for mass transfer, NSt.NSc2/3 is equal to
f/2
A pure drug is administered as a sphere and as a cube. The amount of drug is the same in the two tablets. Assuming that the shape and size do not influence the mass transfer, the ratio of rate of dissolution in water at t = 0 for the cubic to spherical tablet is
1.24
Minimum reflux ratio in a distillation column results in
maximum condenser size.
Flooding in a distillation column is detected by a sharp
increase in pressure drop.
In extraction, as the temperature increases, the area of hetrogeneity (area covered by binodal curve)
decreases
Pick out the wrong statement.
1 Nm3 of dry air is lighter than 1Nm3 of humid air.
In case of an unsaturated mixture of gas and vapor, the percentage saturation is ____ its relative saturation.
lower than
At constant pressure, with increase of temperature, the dew point will
increase
For a single component absorber, the operating line is straight only when plotted in term of ____ units.
mole ratio
In case of unsaturated air
both (a) and (b)
For a binary mixture with low relative volatility,
an azeotrope may be formed during distillation.
Plate efficiency
is a function of the mass transfer between liquid and vapour.
Absorption accompanied by heat evolution results in
decrease in equilibrium solubility.
Even though bubble cap towers are very effective for humidification operation, they are not used commonly in industries, because of the
high pressure drop of the gas.
For a distillation column operating at minimum reflux, the
number of plates required will be maximum.
A solid is being dried in the linear drying rate regime from moisture content Xo to XF. The drying rate is zero at X = 0 and the critical moisture content is the same as the initial moisture Xo. The drying time for M = (Ls/ARc) is (where, L = total mass of dry solid, A = total surface area for drying Rc = Constant maximum drying rate per unit area X = moisture content (in mass of water/mass of dry solids))
MXo ln(Xo/XF)
Flash distillation is suitable for the separation of components
having very wide boiling points.
In Mcabe-Thiele method, at infinite reflux ratio
both the operating lines coincide with the diagram.
Leaching rate is independent of the
none of these
Use of packed towers for distillation is generally limited to the
small sizes.
Pick out the wrong statement.
Molecular diffusion in solid is much faster than that in liquids.
Which of the following decreases during evaporative cooling process with recirculated water supply?
None of these
Laboratory determination of the dif-fusivity of vapor is done by ____ method.
Winkel mann’s
The minimum liquid rate to be used in an absorber corresponds to an operating line
tangential to the equilibrium curve
Unsaturated air (with dry and wet bulb temperatures being 35 and 25°C respectively) is passed through water spray chamber maintained at 35°C. The air will be
humidified
For absorbing a sparingly soluble gas in a liquid, the
liquid side coefficient should be increased.
A natural draft cooling tower is filled with wooden grids, which covers about ____ percent of the tower height.
45580
The boiling points of pure components of a binary system ____ with increase in total pressure of the system.
increases
The change in enthalpy, when a unit quantity of gas is absorbed by relatively large quantity of adsorbent (on which a definite concentration of the adsorbed gas already exists) is termed as the
differential heat of adsorption.
Penetration theory relates the average mass transfer co-efficient (K) with diffusivity (D) as
K ∝sqrt(D)
Desulphurisation of petrol is done in a
rotating disc extractor
Chemisorption compared to physical absorption has
increased utilisation of stagnant zones of the liquid phase.
Rate of adsorption increases as the
temperature decreases.
Pick out the system with maximum boiling azeotrope at 1 atm.
acetone chloroform
At 750°K and 1 atm, the approximate value of Schmidt number for air is
0.1
Calculation of mass transfer co-efficient is mostly/normally done using ____ theory.
film
The velocity, concentration and temperature boundary, for the boundary layer development on a flat plate during connective mass transfer will be same, if
NSc = NPr = NLe
For the gas absorption, the height of a transfer unit, based on the gas phase is given by (G: superficial molar gas velocity, L: superficial molar liquid velocity, FG:mass transfer co-efficient, mols/m2 , a: in-terfacial area per unit volume of tower)
G/FG.a
Which of the following is used for the concentration of rubber latex?
Agitated film evaporator
As the reflux ratio, in a continuous counter-current extraction is increased, the number of stages
decrease
In triangular co-ordinates, the ternery composition point falls ____ of the triangle.
inside
In a single stage extraction process, 10 kg of pure solvent S (containing no solute A) is mixed with 30 kg of feed F containing A at a mass fraction xf = 0.2. The mixture splits into an extract phase E and a raf-finate phase R containing A at xB = 0.5 and xR = 0.05 respectively. The total mass of the extract phase is (in Kg)
8.89
Penetration theory states that the mass transfer co-coefficient is equal to (where, De is diffusivity and ‘t’ is time)
(4De/πt)^1/2
Reboiler is considered as one theoretical plate, because
of the assumption that vapour and liquid leaving the reboiler are in equilibrium.
