Mass Transfer Flashcards
Mass transfer rate between two fluid phases does not necessarily depend on the __________ of the two phases.
chemical properties
physical properties
degree of turbulence
interfacial area
chemical properties
In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the molality is
0.50
0.60
2
1
0.50
Fenske equation determines the
maximum number of ideal plates.
height of the distillation column.
minimum number of theoretical plates.
optimum reflux ratio.
minimum number of theoretical plates.
The term “cooling range” in a cooling tower refers to the difference in the temperature of
cold water leaving the tower and the wet bulb temperature of the surrounding air.
hot water entering the tower and the wet bulb temperature of the surrounding air.
hot water entering the tower and the cooled water leaving the tower.
none of these
hot water entering the tower and the cooled water leaving the tower.
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
Centrifugal extractor
Total reflux in a distillation operation requires minimum
reboiler load
number of plates
condenser load
all (a), (b) and (c)
number of plates
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) and (b).
neither (a) nor (b).
both (a) and (b).
The difference of wet bulb temperature and adiabatic saturation temperature of unsaturated mixture of any system is
+ve
-ve
zero
none of these
+ve
Fenske’s equation for determining the minimum number of theoretical stages in distillation column holds good, when the
relative volatility is reasonably constant.
mixture (to be separated) shows negative deviation from ideality.
mixture (to be separated) shows positive deviation from ideality.
multicomponent distillation is involved.
relative volatility is reasonably constant.
When the temperature and humidity of air is low, we usually use __________ draft cooling tower.
natural
forced
induced
none of these
natural
Pick out the correct statement.
In case of liquid-liquid extraction, no separation is possible, if the selectivity of the solvent used is unity.
With increase in temperature, the selectivity of the solvent used in solvent extraction decreases.
The selectivity of solvent used in solvent extraction is unity at the plait point.
all (a), (b) and (c).
all (a), (b) and (c).
__________ columns are used for liquid dispersion in a continuous gas phase.
Packed
Pulse
Bubble cap
Sieve plate
Packed
Overall efficiency of the distillation column is
the ratio of number of ideal plates to actual plates.
the ratio of number of actual plates to ideal plates.
same as the Murphree efficiency.
always more than the point efficiency.
the ratio of number of ideal plates to actual plates.
Which is the controlling factor for a drum drier?
Diffusion
Heat transfer
Both (a) and (b)
Neither (a) nor (b)
Heat transfer
Drying operation under vacuum is carried out to
dry those materials which have very high unbound mositure content.
reduce drying temperature.
increase drying temperature.
dry materials having high bound moisture content.
reduce drying temperature.
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.
higher relative humidity
Separation of two or more components of a liquid solution can not be achieved by
fractional crystallisation
liquid extraction
absorption
evaporation
absorption
Stefan’s law describes the mass transfer by
diffusion
bulk flow
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’
both ‘a’ & ‘b’
At minimum reflux ratio for a given separation
number of plates is zero.
number of plates is infinity.
minimum number of the theoretical plates is required.
separation is most efficient.
number of plates is infinity.
Relative humidity is the ratio of the
partial pressure of the vapour to the vapour pressure of the liquid at room temperature.
partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.
actual humidity to saturation humidity.
none of these
partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.
In batch distillation with constant reflux, overhead product composition __________ with time.
increases
decreases
does not vary
may increase on decrease, depends on the system.
decreases
Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the __________ of a fibre.
electrical resistance
thermal conductivity
strength
none of these.
electrical resistance
Heat in BTU necessary to increase the temperature of 1 lb of gas and its accompanying vapour by 1°F is called the
latent heat
humid heat
specific heat
sensible heat
specific heat
To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)
increase both ‘G’ and ‘S’.
decrease both ‘G’ and ‘S’.
increase ‘S’ and decrease ‘G’.
increase ‘G’ and decrease ‘S’
increase ‘S’ and decrease ‘G’.
The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are same for, NPr = NSc = __________
1
0.5
10
0
1
Dew point of a gas-vapour mixture
increases with temperature rise.
decreases with temperature rise.
decreases with decrease in pressure.
increases with increase in pressure.
decreases with decrease in pressure.
In a packed absorption tower, if the equilibrium and operating lines are both straight lines, then the ratio, HETP/HTUOG __________ the absorption factor.
increases with increase in
is one at unity value of
both (a) and (b)
neither (a) nor (b)
both (a) and (b)
Which of the following plays an important role in problems of simultaneous heat and mass transfer ?
Lewis number
Schmidt number
Prandtl number
Sherwood number
Lewis number
In case of an absorber, the operating
line always lies above the equilibrium curve.
line always lies below the equilibrium curve.
line can be either above or below the equilibrium curve.
velocity is more than the loading velocity.
line always lies above the equilibrium curve.
As the reflux ratio in a distillation coloumn is increased from the minimum, the
slope of the operating line in stripping section decreases.
number of plates decreases very slowly first and then more and more rapidly.
total cost first decreases and then increases.
liquid flow increases while the vapor flow decreases for a system.
total cost first decreases and then increases.
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
S1/S2
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 ?
0
1
2
3
0
Which of the following remains constant during sensible cooling process ?
Specific humidity
Partial pressure of vapour
Both (a) and (b)
Neither (a) nor (b)
Both (a) and (b)
Make up water is required in a cooling tower to replace the water lost by
evaporation
drift
blowdown and leakage
all (a), (b) and (c)
all (a), (b) and (c)
Which of the following quantities need not be fixed before starting the design of a co-current absorber ?
Heat gain or loss
Flow rate of entering liquid
Flow rate of gas
None of these
Flow rate of entering liquid
Mass transfer co-efficient of liquid is
affected more by temperature than that for gases.
affected much less by temperature than that for gases.
not affected by the temperature.
none of these.
affected more by temperature than that for gases.
Absorption accompanied with chemical reaction is exemplified by the absorption of
ammonia in water.
benzol present in coke oven gas by wash oil.
SO2 in alkaline solution.
all (a), (b) and (c).
SO2 in alkaline solution.
Which of the following unit operations makes use of Thiele-Geddes equation ?
Liquid-liquid extraction
Solid-liquid extraction
Multicomponent absorption with chemical reaction
Multicomponent distillation.
Multicomponent distillation.
Which of the following liquid-vapor contacting devices provides maximum contact surface area for a particular duty ?
Sieve plate column
Bubble cap column
Randomly packed column
Wetted wall column
Wetted wall column
The equipment frequently used for adiabatic humidification-cooling operation with recirculating liquid is
natural draft cooling tower
induced draft cooling tower
spray chamber
none of these
spray chamber
Chemisorption (chemical adsorption) is
same as “Van der Waals” adsorption.
characterised by adsorption of heat.
an irreversible phenomenon.
a reversible phenomenon.
an irreversible phenomenon.
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 ‘a’, ‘b’ & ‘c’.
all ‘a’, ‘b’ & ‘c’.
Raoult’s law applies to the
all liquid solutions
non-ideal solution only.
non-volatile solute.
solvents.
solvents.
In distillation columns, the number of bubble caps per tray primarily depends upon the
allowable liquid velocity.
allowable gas velocity.
allowable gas and liquid velocities.
feed composition.
allowable gas and liquid velocities.
In distillation, overhead product contains
only one component
two components
any number of components
only saturated liquid
any number of components
With increase in pressure, the relative volatility for a binary system
increases.
decreases.
remains same.
either (a) or (b), depends on the system.
decreases
Low viscosity absorbent is preferred for reasons of
rapid absorption rates and good heat transfer characteristics.
improved flooding characteristics.
low pressure drop on pumping.
all (a), (b) and (c).
all (a), (b) and (c).
Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as
K ∝ D
K ∝ √D
K ∝ D^1.5
K ∝ D^2
K ∝ D
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.
linear crystal growth rate does not depend on the crystal size.
Bollman extractor
is a static bed leaching equipment.
is used for extraction of oil from oilseed.
is a centrifugal extractor.
employs only counter-current extraction.
is used for extraction of oil from oilseed.
The relation, Sc = Pr = 1, is valid, when the mechanism of __________ ansfer is same.
heat and mass
mass and momentum
heat and momentum
heat, momentum and mass
heat and mass
A coalescer in a mixer-settler liquid-liquid extraction coloumn
comprises of thin bed of substances of extended surface having high porosity.
helps in increasing the bubble size entering the settler.
helps in increasing the settling rate of the bubbles.
all ‘a’, ‘b’, & ‘c’.
all ‘a’, ‘b’, & ‘c’.
For the same feed, feed quality and separation (in a distillation column), with the increase of total pressure, the number of ideal plates will
increase
decrease
remain same
data insufficient, can’t be predicted
increase
Pick out the correct statement.
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.
A sharp decrease in pressure drop is an indication of flooding in a distillation coloumn.
Solvent used in extractive distillation should be of high volatility.
Flash distillation is suitable for separating components which have very close boiling temperature.
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.
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.
vapour pressure of component A to that of component B.
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
elutriation or elution
In the constant rate period of the rate of drying curve for batch drying,
cracks develop on the surface of the solid.
rate of drying decreases abruptly.
surface evaporation of unbound moisture occurs.
none of these.
surface evaporation of unbound moisture occurs.
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%).
15 min
51 min
71 min
94 min
71 min
Agitator is provided in a crystalliser for
avoiding deposition on cooler surfaces.
formation of nuclei.
crystal growth.
all (a), (b) and (c).
all (a), (b) and (c).
__________ diffusion is used for separating the isotopes of methane.
Thermal
Pressure
Concentration
Force
Thermal
Ordinary diffusion process is also called __________ diffusion.
pressure
thermal
concentration
forced.
concentration
Pick out the wrong statement.
Different solids have different equilibrium moisture curves.
Total condenser or reboiler is considered equivalent to one theoretical plate in McCabe-Thiele method of theoretical plate calculation for distillation column.
Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column.
Even a forced draft cooling tower can not cool water below the wet bulb temperature.
Heat removal load on cooler remains constant, even with increase of the reflux ratio in a distillation column.
Pick out the wrong statement pertaining to the rotary dryer.
Flights (located in the inside shell of rotary dryer) lift the material being dried and shower it down through the current of hot air/gases. It extends from the wall to a distance which is about 8-12% of the inside diameter of shell.
Hold up of a rotary drier is defined as the fraction of the dryer volume occupied by the solid at any instant. The best performance for rotary drier is obtained, when the hold up is in the range of 0.05 to 0.15.
Rotary dryer is suitable for drying sticky material.
Recommended peripherial speed of a rotary drier is in the range of 10 to 30 metres/minute.
Rotary dryer is suitable for drying sticky material.
The reason for preferring packed towers over plate towers in distillation practice is that the packed tower operation gives
low pressure drop and high hold up.
high pressure drop and low hold up.
low pressure drop and low hold up.
high pressure drop and high hold up.
low pressure drop and low hold up.
If the path of liquid across the plate is very long as in case of large diameter tower, Murphree efficiency can be __________ percent.
100
> 100
< 100
none of these
> 100
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
25%
50%
70%
90%
50%
Raoult’s law is applicable to the
ideal solutions
real solutions
mixture of water and alcohol
non-ideal gases
ideal solutions
Weeping in a distillation column
increases tray efficiency.
provides large interfacial surface for mass transfer.
results due to very high gas velocity.
results due to very low gas velocity.
results due to very low gas velocity.
In case of binary distillation, increasing the reflux ratio above optimum does not result in the increase of
area between operating line and 45° diagonal x-y diagram.
condenser and reboiler surfaces.
tower cross-section.
none of these.
area between operating line and 45° diagonal x-y diagram.
Wetted wall tower experiment determines the
molal diffusivity.
volumetric co-efficient.
mass transfer co-efficient.
none of these.
mass transfer co-efficient.
In McCabe-Thiele method, at infinite reflux ratio
the overhead product is minimum.
both the operating lines coincide with diagonal.
both (a) and (b).
neither (a) nor (b).
the overhead product is minimum.
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
increases
Plate towers are preferred to packed towers, when large temperature changes are involved, because of the reason that the
packing may be crushed due to thermal expansion/contraction of the components of the equipments.
pressure drop in the equipment will be . very high.
viscosity variation of the fluids may cause channeling/flooding.
none of these.
packing may be crushed due to thermal expansion/contraction of the components of the equipments.
The equilibrium liquid composition compared to the vapor composition in case of azeotropic mixture is
more
less
same
either more or less; depends on the system
same
Out of the following gas-liquid contacting devices, for a given set of operating conditions, gas pressure drop is the least in __________ tower.
wetted wall
bubble cap
perforated tray
packed
wetted wall
Pick out the system with minimum boiling azeotrope at 1 atm.
benzene-toluene
ethyl alcohol-water
hydrochloric acid-water
all (a), (b) and (c)
ethyl alcohol-water
Free flowing granular materials can be best dried in a __________ drier.
rotary
cylinder
drun
freeze
rotary
In case of an ideal solution, the total vapor pressure varies __________ with the composition expressed as mole fraction,
inversely
linearly
exponentially
none of these
linearly
Corresponding to Nusselt number in heat transfer, the dimensionless group in mass transfer is the __________ number.
Sherwood
Schmidt
Peclet
Stanton
Sherwood
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
0.31
0.107
0.017
0.215
0.215
Liquid diffusivity is of the order of __________ cm2 /second.
0.01
0.1
10-5 to 10-6
> 1
10-5 to 10-6
The solvent used in liquid extraction should not have high latent heat of vaporisation, because
the pressure drop and hence the pumping cost will be very high.
it cannot be recovered by distillation.
its recovery cost by distillation may be prohibitatively high.
it will decompose while recovering by distillation.
its recovery cost by distillation may be prohibitatively high.
At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid __________ that in dry packed tower.
is greater than
is lower than
is same as
cannot be predicted as data are insufficient
is greater than
Molarity is defined as the number of gm moles of solute per __________ of solvent.
litre
kg
gm
c.c
litre
The value of Lewis number (Le = Sc/Pr) for air-water vapour system is around
1
0.24
3.97
600
1
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)
less number of trays are required.
composition of the residue remains unchanged.
more number of trays are required but the residue composition remains unchanged.
more number of trays are required and the residue composition is more dilute in methanol.
less number of trays are required.
The partial pressure distribution of an ideal gas diffusing through another stagnant ideal gas at steady state follows a/an __________ law.
exponential
parabolic
linear
cubic
exponential
Which of the following binary systems is an example of a maximum boiling azeotrope ?
Water-hydrochloric acid.
Acetone-carbon disulphide.
Water-ethyl alcohol.
n-heptane-n-octane.
Water-hydrochloric acid.
(NRe . NSc) is termed in mass transfer operation as the __________ number.
Stanton
Sherwood
Peclet
none of these
Peclet
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
T^3/2 and T
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.
In Ponchon-Savarit method of no. of theoretical plate determination, the stripping and rectifying operating lines are vertical at total reflux.
Pick out the correct statement.
Dialysis process is used for the production of fresh water from brine.
Electrodylsis is used in the manufacture of NaOH.
Electrodylsis is used for the refin-ning/purification of petrol.
both (b) and (c).
Electrodylsis is used in the manufacture of NaOH.
Pick out the correct statement.
Bound moisture is removed during constant rate drying period.
Free moisture is removed during falling rate drying period.
The sum of free moisture and equilibrium moisture in a solid is called the critical moisture.
The driving force for mass transfer in a wet solid is its free moisture content.
The driving force for mass transfer in a wet solid is its free moisture content.
Very tall packed towers are divided into series of beds to
reduce the overall pressure drop
avoid channelling
reduce liquid hold-up
avoid flooding
avoid channelling
Moisture contained by a substance in excess of the equilibrium moisture is called the __________ moisture.
unbound
free
critical
bound
free
With increase in temperature, the solubility of gases in liquids, at fixed pressure
increases
decreases
remains same
either (a) or (b), depends on the system
decreases
In most of the vacuum crystalliser, vacuum is generally produced by means of a
suction pump
compressed air jet
steam jet ejector with a barometric condenser
none of these
steam jet ejector with a barometric condenser
On moving the feed line (q-line) from saturated liquid feed (vertical position) to saturated vapor feed (horizontal feed), if the slope of both the operating lines are to be increased, then it will result in
greater degree of separation with a fixed number of trays
increased reboiler load
increased reflux ratio
None of these.
increased reflux ratio
__________ column is the most suitable for achieving the best performance for mass transfer operations involving liquid with dispersed solids.
Watted wall
Packed
Plate
Spray
Plate
Deairation (removal of O2) of water is done by
rectification
absorption
ion-exchange
adsorption
ion-exchange
Make up water is supplied during cooling tower operation to compensate for water losses due to
evaporation
blowdown
entrainment
all (a), (b)&(c)
all (a), (b)&(c)
Pick out the wrong statement.
The mole fraction of solute is directly proportional to the molality of a ‘dilute’ solution.
For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both components is nonlinear in the case of steady state unimolal unidirectional diffusion.
Azeotropes obey Raoult’s law at all temperature.
The relative volatility of a binary mixture at the azeotropic composition is 1.
Azeotropes obey Raoult’s law at all temperature.
A minimum boiling azeotrope is exemplified by
toluene-benzene
acetone-carbon disulphide
water-isobutyl alcohol
none of these
acetone-carbon disulphide
Which of the following solutions will follow Raoult’s law most closely ?
A solution of benzene, toluene and oxylene.
35% solution of camphor in water.
35% solution of NH3 in water.
A solution of polar organic compounds (not of homologs of a series).
A solution of benzene, toluene and oxylene.
Use of raschig rings in place of crushed stones as packing in packed beds (other things being same)
increases pressure drop, increases surface area.
increases pressure drop, decreases surface area.
decreases pressure drop, increases surface area.
decreases pressure drop, decreases surface area.
decreases pressure drop, increases surface area.
The assumption made in Elis method in distillation is that enthalpy concentration lines of vapor and liquid are
parallel
straight
both parallel and straight
neither parallel nor straight
both parallel and straight
As complete saturation of an adsorbent is approached, the differential heat of adsrop-tion approaches
that of normal condensation.
integral heat of adsorption.
zero.
none of these.
that of normal condensation.
Absorption with chemical reaction’ is involved in the removal of
carbon dioxide from gaseous stream using alkaline solution.
benzol from coke oven gas using solar oil/wash oil.
ammonia from coke oven gas using refrigerated water.
tar from coke oven gas in primary gas coolers using chilled water.
carbon dioxide from gaseous stream using alkaline solution.
The-relative volatility for separation of a non-ideal binary mixture by distillation should be
0
1
> 1
< 1
> 1
Pick out the wrong statement:
Reboiler is not used in open steam distillation.
The separation of solutes of different molecular sizes in a liquid solution by use of a suitable membrane is called dialysis.
Freeze drying is used for the drying of fish.
Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.
Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.
In paper industry, paper is dried in a __________ dryer.
tunnel
heated cylinder
conveyor
festoon
heated cylinder
Pick out the wrong statement.
Critical moisture content is not a property of the material itself.
A sharp increase in pressure drop gives an indication of the flooding in a distillation column.
Separation of components is not possible in liquid extraction, if selectivity is unity.
Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.
Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.
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
large latent heat
The most common packing used in industrial operations is __________ rings.
raschig
lessing
cross-partition
single spiral
raschig
When the feed to a distillation column is a saturated liquid, slope of the feed line is
zero
unity
infinity
none of these
infinity
Leaching of sugar from sugar beets is done by
hot water
hexane
dilute H2SO4
lime water
hot water
Absorption factor method is used to calculate the number of ideal stages, when
operating line lies above the equilibrium line.
operating line lies below the equilibrium line.
both operating and equilibrium lines are parallel.
pressure drop in the column is very high.
both operating and equilibrium lines are parallel.
Flights in a rotary dryer are provided to
lift and shower the solids thus exposing it thoroughly to the drying action of the gas.
reduce the residence time of solid.
increase the residence time of the solid.
none of these.
lift and shower the solids thus exposing it thoroughly to the drying action of the gas.
If f = moles of vapour present per mole of feed, then the slope of feed line is (Mcabe-Thiele method)
1-f/f
-(f-1)/f
-1/f
-f/1-f
-1/f
If the solubilities of different components (in a liquid-liquid extraction system) increase with rise in temperature, then the temperature above which they dissolve completely is known as the critical solution temperature (CST or consolute temperature). If solubilities increase with decrease in temperature, then CST is the temperature below which they dissolve completely. If a binary system has no critical solution temperature, it implies that
the system comprises of partially mis-cible liquids.
the system comprises of miscible liquids.
the system comprises of an azeotrope.
on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.
on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.
The rate of mass transfer is not dependent upon the
degree of dispersion of one fluid in the other.
interfacial surface exposed between the phases.
both (a) & (b).
none of these.
none of these.
At equilibrium the concentration of water in vapour phase (C)in kg/m3 of air space and the amount of water (m) adsorbed per kg of dry silica gel are related by, C = 0.0667m. To maintain dry conditions in a room of air space 100m3 containing 2.2 kg of water vapour initially, 10 kg of dry silica gel is kept in the room. The fraction of initial water remaining in the air space after a long time (during which the temperature is maintained constant) is
0.0
0.2
0.4
1.0
0.4
Dry bulb temperature of unsaturated air is more than its __________ temperature.
dew point
wet bulb
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’
both ‘a’ & ‘b’
For the case of flow of air past a wet bulb thermometer (air water vapour system), the approximate value of h2/ky.Cz is around
0.60
0.24
1
0.72
1
The reciprocal of stripping factor is termed as
selectivity index
relative volatility
absorption factor
Murphree efficiency
absorption factor
Ponchan-Savarit method analyses the fractional equipment based on
enthalpy balance only.
material balance only.
both enthalpy and material balances.
the assumption of constant molaloverflow.
both enthalpy and material balances.
The binary diffusivity in gases at atmospheric conditions is about
10-9 cm/sec
10-1 cm2/sec
10-3 sec/cm
10-4 cm2/sec2
10-1 cm2/sec
Percentage saturation is __________ the relative saturation.
always smaller than
always greater than
not related to
none of these
always smaller than
In case of a desorber (stripper), the
operating line always lies above the equilibrium curve.
operating line always lies below the equilibrium curve.
temperature remains unaffected.
temperature always increases.
operating line always lies below the equilibrium curve.
What is the reflux ratio at total reflux ?
Zero
Infinity
Unity
Data insufficient
Infinity
Under conditions of flooding in packed tower, the gas pressure drop
decreases rapidly
increases rapidly
remains constant
is maximum
is maximum
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
10-60
For absorbing a sparingly soluble gas in a liquid
gas side mass transfer co-efficient should be increased.
liquid side mass transfer co-efficient should be increased.
liquid side mass transfer co-efficient should be decreased.
mass transfer co-efficient must be kept constant.
liquid side mass transfer co-efficient should be increased.
The change in enthalpy per unit weight of adsorbed gas when adsorbed on gas free or “outgassed” adsorbent to from a definite concentration of adsorbate is called its
integral heat of adsorption.
heat of wetting.
differential heat of adsorption.
heat of normal condensation.
integral heat of adsorption.
The minimum number of theoretical plates is required for achieving a given separation in distillation column with ____.
no reflux
total reflux
zero reflux ratio
minimum reflux ratio
total reflux
A good solvent used for absorption should not have very high
viscosity
vapor pressure
freezing point
all (a), (b) & (c)
all (a), (b) & (c)
In a counter-current liquid extractor
both liquids flow at fixed rate.
both liquids can have any desired flow rate.
only one of the liquids may be pumped at any desired rate.
liquid’s flow rate depends upon the temperature and pressure.
only one of the liquids may be pumped at any desired rate.
Which of the following is an undesirable property for an absorbing solvent ?
Low vapour pressure
Low velocity
Low freezing point
None of these
None of these
The wetted wall tower is used to determine
individual mass transfer co-efficient (M.T.C.) in gaseous system.
M.T.C. of individual components in a liquid-liquid system.
M.T.C. of liquid in liquid-gas system.
the overall M.T.C. of the system.
individual mass transfer co-efficient (M.T.C.) in gaseous system.
Weight of 1 m3 of humid air as compared to 1 m3 of dry air, under the same conditions, is
less
more
same
unpredictable
less
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.
greater than that computed for ideality.
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
increases
Schmidt number is given by
μ/ρD_AB
Re.Pe
Sh x Pe
Re/Pe
μ/ρD_AB
Prandtl number for water at 20°C is about
7
70
0.7
150.
7
Boiling point diagram is
not affected by pressure.
affected by pressure.
a plot of temperature vs. liquid composition.
a plot of temperature vs. vapour composition.
affected by pressure.
When acetone is added in a two layer mixture of methyl isobutyl ketone and water at 30°C, the acetone distributes between the two layers and the composition of the layer follows two solubility curves. For this system,
as the acetone concentration increases, the solubility curves approach each other.
both the phases become identical at a particular common point on both the solubility curves called the plait point.
the distribution curve which is a plot between x (acetone concentration in one phase) and y (acetone concentration in other phase) is analogous to x-y curve used in distillation and absorption terminates on the x = y diagonal at the concentration of the plait point.
all (a), (b) and (c).
all (a), (b) and (c).
Steam distillation is used to
reduce the number of plates.
avoid thermal decomposition of a component.
increase the efficiency of separation.
increase the total pressure of distillation.
avoid thermal decomposition of a component.
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.
dilute solutions, over a small concentration range.
For ethanol-water system, the lowering of distillate quality from 95% to 92% will cause __________ plate requirement.
no change in theoretical
marginal decrease in the number of
major decrease in the number of
none of these
marginal decrease in the number of
The apex of an equilateral-triangular coordinate (in ternary liquid system) represents a/an
pure component
binary mixture
ternary mixture
insoluble binary system
pure component
The diffusivity (D) in a binary gas mixture is related to the pressure (P) as
D ∝ P^0.5
D ∝ 1/P^0.5
D ∝ 1/P
D ∝ 1/P^1.5
D ∝ 1/P
A slurry is to be dried to produce flaky solid. Which dryer would you recommend ?
Spray dryer
Drum dryer
Rotary dryer
Dielectric dryer
Spray dryer
Which of the following psychrometric processes is followed by water vapour laden unsaturated air, when it is passed through solid or liquid adsorbent ?
Cooling and dehumidification.
Heating and dehumidification at almost constant wet bulb temperature.
Dehumidification with dry bulb temperature remaining constant.
None of these.
Heating and dehumidification at almost constant wet bulb temperature.
In gas-liquid contact operation, the number of ideal stages, N=(Xa-Xb)/(Xb-Xb*) . This is true when the stripping factor ‘S’ is
S > 1
S < 1
S = 1
S = ∞
S > 1
