mt Flashcards
Mass transfer rate between two fluid phases does not necessarily depend
on the __________ of the two phases.
chemical properties
In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the
molality is
0.50
Fenske equation determines the
minimum number of theoretical plates.
- The term “co” in a cooling tower refers to the difference in the temperature
of
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?
centrifugal extractor
Total reflux in a distillation operation requires minimum
number of plates
The difference of wet bulb temperature and adiabatic saturation temperature
of unsaturated mixture of any system is
+ve
Fenske’s equation for determining the minimum number of theoretical
stages in distillation column holds good, when the
relative volatility is reasonably constant
When the temperature and humidity of air is low, we usually use
__________ draft cooling tower
natural
Pick out the correct statement.
a. In case of liquid-liquid extraction, no separation is possible, if the
selectivity of the solvent used is unity.
b. With increase in temperature, the selectivity of the solvent used in
solvent extraction decreases.
c. The selectivity of solvent used in solvent extraction is unity at the
plait point.
d. all (a), (b) and (c).
d. all (a), (b) and (c).
__________ columns are used for liquid dispersion in a continuous gas
phase
packed
Overall efficiency of the distillation column is
the ratio of number of ideal plates to actual plates.
Drying operation under vacuum is carried out to
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 relative humidity
Separation of two or more components of a liquid solution can not be
achieved by
absorption
Stefan’s law describes the mass transfer by
diffusion and bulk flow
At minimum reflux ratio for a given separation
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
gas temperature.
In batch distillation with constant reflux, overhead product composition
__________ with time
decreases
Psychrometry deals with the properties of gas-vapor mixture. Humidity
can be determined by the measurement of the __________ of a fibre.
electric resistance
Heat in BTU necessary to increase the temperature of 1 lb of gas and its
accompanying vapour by 1°F is called the
specific heat
To increase the absorption factor, (where, G = gas flow rate, S = solvent
flow rate)
increase S decrease G
The mass diffusivity, the thermal diffusivity and the eddy momentum
diffusivity are same for, NPr = NSc = __________
1
Dew point of a gas-vapour mixture
decreases with decrease in pressure.
Which of the following plays an important role in problems of
simultaneous heat and mass transfer ?
LEWIS NUMBER
In case of an absorber, the operating
line always lies above the equilibrium curve
As the reflux ratio in a distillation coloumn is increased from the
minimum, the
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)
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
Make up water is required in a cooling tower to replace the water lost by
ALL A B C
Which of the following quantities need not be fixed before starting the
design of a co-current absorber?
FLOWRATE OF ENTERING LIQUID
Absorption accompanied with chemical reaction is exemplified by the
absorption of
SO2 IN ALKALINE SOLUTION
Which of the following unit operations makes use of Thiele-Geddes
equation ?
MULTICOMPONENT DISTILLATION
Which of the following liquid-vapor contacting devices provides
maximum contact surface area for a particular duty?
a. Sieve plate column
b. Bubble cap column
c. Randomly packed column
d. Wetted wall column
WETTED WALL
The equipment frequently used for adiabatic humidification-cooling
operation with recirculating liquid is
a. natural draft cooling tower
b. induced draft cooling tower
c. spray chamber
d. none of these
SPRAY CHAMBER
- Chemisorption (chemical adsorption) is
a. same as “Van der Waals” adsorption.
b. characterised by adsorption of heat.
c. an irreversible phenomenon.
d. a reversible phenomenon.
AN IRREVERSIBLE PHENOMENON
The rate of solid-liquid extraction is limited by the
a. phase change of the solute as it dissolves in the solvent.
b. diffusion of the solute through the solvent in the pores to the
outside of the particle.
c. diffusion of the solute from the solution in contact with the particle
to the main bulk of the solution.
d. all ‘a’, ‘b’ & ‘c’.
ALL A B C
Raoult’s law applies to the
a. all liquid solutions
b. non-ideal solution only.
c. non-volatile solute.
d. solvents.
SOLVENTS
In distillation columns, the number of bubble caps per tray primarily
depends upon the
a. allowable liquid velocity.
b. allowable gas velocity.
c. allowable gas and liquid velocities.
d. feed composition.
ALLOWABLE GAS AND LIQUID VELOCITIES
In distillation, overhead product contains
a. only one component
b. two components
c. any number of components
d. only saturated liquid
ANY NUMBER OF COMPONENTS
With increase in pressure, the relative volatility for a binary system
a. increases.
b. decreases.
c. remains same.
d. either (a) or (b), depends on the system.
DECREASES
Low viscosity absorbent is preferred for reasons of
a. rapid absorption rates and good heat transfer characteristics.
b. improved flooding characteristics.
c. low pressure drop on pumping.
d. all (a), (b) and (c).
ALL A B C
Mass transfer co-efficient (K) and diffusivity (D) are related according to
film theory as
a. K ∝ D
b. K ∝(D)^1/2
c. K ∝ D1.5
d. K ∝ D2
K ∝ D
The McCabe Δ L law states that the
a. molar heats of vaporisation of components are nearly equal.
b. linear crystal growth rate depends on the degree of supersaturation.
c. linear crystal growth rate does not depend on the crystal size.
d. linear crystal growth rate depends on the crystal size.
c. linear crystal growth rate does not depend on the crystal size.
Bollman extractor
a. is a static bed leaching equipment.
b. is used for extraction of oil from oilseed.
c. is a centrifugal extractor.
d. employs only counter-current extraction.
b. is used for extraction of oil from oilseed.
The relation, Sc = Pr = 1, is valid, when the mechanism of __________
ansfer is same.
a. heat and mass
b. mass and momentum
c. heat and momentum
d. heat, momentum and mass
heat and mass
A coalescer in a mixer-settler liquid-liquid extraction coloumn
a. comprises of thin bed of substances of extended surface having
high porosity.
b. helps in increasing the bubble size entering the settler.
c. helps in increasing the settling rate of the bubbles.
d. 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
a. increase
b. decrease
c. remain same
d. data insufficient, can’t be predicted
increase
. Pick out the correct statement.
a. 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.
b. A sharp decrease in pressure drop is an indication of flooding in a
distillation coloumn.
c. Solvent used in extractive distillation should be of high volatility.
d. 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
a. vapour pressure of component A to that of component B.
b. vapour pressure of component A to the total pressure.
c. vapour pressure of component A to the partial pressure of A.
d. 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
elutriation or elution
In the constant rate period of the rate of drying curve for batch drying,
a. cracks develop on the surface of the solid.
b. rate of drying decreases abruptly.
c. surface evaporation of unbound moisture occurs.
d. 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%).
71 min
Agitator is provided in a crystalliser for
a. avoiding deposition on cooler surfaces.
b. formation of nuclei.
c. crystal growth.
d. all (a), (b) and (c).
all a b c
__________ diffusion is used for separating the isotopes of methane.
thermal
Ordinary diffusion process is also called __________ diffusion.
concentration
Pick out the wrong statement.
a. Different solids have different equilibrium moisture curves.
b. Total condenser or reboiler is considered equivalent to one
theoretical plate in McCabe-Thiele method of theoretical plate
calculation for distillation column.
c. Heat removal load on cooler remains constant, even with increase
of the reflux ratio in a distillation column.
d. 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.
a. 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.
b. 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.
c. Rotary dryer is suitable for drying sticky material.
d. Recommended peripherial speed of a rotary drier is in the range of
10 to 30 metres/minute.
c. 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
a. low pressure drop and high hold up.
b. high pressure drop and low hold up.
c. low pressure drop and low hold up.
d. 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
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
50%
Raoult’s law is applicable to the
ideal solutions
Weeping in a distillation column
a. increases tray efficiency.
b. provides large interfacial surface for mass transfer.
c. results due to very high gas velocity.
d. results due to very low gas velocity.
d. 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
a. area between operating line and 45° diagonal x-y diagram.
b. condenser and reboiler surfaces.
c. tower cross-section.
d. none of these.
area between operating line and 45 diagonal x-y diagram
Wetted wall tower experiment determines the
mass transfer co-efficient
n McCabe-Thiele method, at infinite reflux ratio
the overhead product is minimum
With decrease in the throughput (compared with the design capacity) for a
bubble cap distillation column, its efficiency
increases
Plate towers are preferred to packed towers, when large temperature
changes are involved, because of the reason that the
a. packing may be crushed due to thermal expansion/contraction of
the components of the equipments.
b. pressure drop in the equipment will be . very high.
c. viscosity variation of the fluids may cause channeling/flooding.
d. 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
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
Pick out the system with minimum boiling azeotrope at 1 atm.
a. benzene-toluene
b. ethyl alcohol-water
c. hydrochloric acid-water
d. all (a), (b) and (c)
ethyl-alcohol water
Free flowing granular materials can be best dried in a __________ drier.
a. rotary
b. cylinder
c. drun
d. freeze
rotary
In case of an ideal solution, the total vapor pressure varies __________
with the composition expressed as mole fraction,
a. inversely
b. linearly
linearly
Corresponding to Nusselt number in heat transfer, the dimensionless group
in mass transfer is the __________ number.
a. Sherwood
b. Schmidt
c. Peclet
d. 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
0.215
Liquid diffusivity is of the order of __________ cm2 /second.
10^-5 to 10^-6
The solvent used in liquid extraction should not have high latent heat of
vaporisation, because
a. the pressure drop and hence the pumping cost will be very high.
b. it cannot be recovered by distillation.
c. its recovery cost by distillation may be prohibitatively high.
d. 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.
greater than
The value of Lewis number (Le = Sc/Pr) for air-water vapour system is
around
1
Molarity is defined as the number of gm moles of solute per __________
of solvent.
liter
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)
a. less number of trays are required.
b. composition of the residue remains unchanged.
c. more number of trays are required but the residue composition
remains unchanged.
d. 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.
a. exponential
b. parabolic
c. linear
d. cubic
exponential
Which of the following binary systems is an example of a maximum
boiling azeotrope ?
a. Water-hydrochloric acid.
b. Acetone-carbon disulphide.
c. Water-ethyl alcohol.
d. n-heptane-n-octane
water-hydrochloric acid
(NRe . NSc) is termed in mass transfer operation as the __________
number.
a. Stanton
b. Sherwood
c. Peclet
d. none of these
peclet
The binary diffusivity in gases and liquids vary respectively as
T3/2 and T
Pick out the correct statement.
a. The slope of the stripping line is always less than unity.
b. 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.
c. In Ponchon-Savarit method of no. of theoretical plate
determination, the stripping and rectifying operating lines are
vertical at total reflux.
d. 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.
Very tall packed towers are divided into series of beds to
a. reduce the overall pressure drop
b. avoid channelling
c. reduce liquid hold-up
d. avoid flooding
avoid chanelling
Pick out the correct statement.
a. Bound moisture is removed during constant rate drying period.
b. Free moisture is removed during falling rate drying period.
c. The sum of free moisture and equilibrium moisture in a solid is
called the critical moisture.
d. The driving force for mass transfer in a wet solid is its free
moisture content.
the driving force for mass rtansfer in a wet solid is its free moisture content
- Moisture contained by a substance in excess of the equilibrium moisture is
called the __________ moisture.
free
With increase in temperature, the solubility of gases in liquids, at fixed
pressure
decreases
In most of the vacuum crystalliser, vacuum is generally produced by
means of a
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
increased reflux ratio
_________ column is the most suitable for achieving the best performance
for mass transfer operations involving liquid with dispersed solids.
plate
Deairation (removal of O2) of water is done by
a. rectification
b. absorption
c. ion-exchange
d. adsorption
ion-exchange
Make up water is supplied during cooling tower operation to compensate
for water losses due to
a. evaporation
b. blowdown
c. entrainment
d. all (a), (b)&(c)
all a b c
Pick out the wrong statement.
a. The mole fraction of solute is directly proportional to the molality
of a ‘dilute’ solution.
b. 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.
c. Azeotropes obey Raoult’s law at all temperature.
Azeotropes obey Raoult’s law at all temperature.
minimum boiling azeotrope is exemplified by
a. toluene-benzene
b. acetone-carbon disulphide
c. water-isobutyl alcohol
d. none of these
acetone-carbon disulphide
Which of the following solutions will follow Raoult’s law most closely ?
a. A solution of benzene, toluene and oxylene.
b. 35% solution of camphor in water.
c. 35% solution of NH3 in water.
d. 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)
a. increases pressure drop, increases surface area.
b. increases pressure drop, decreases surface area.
c. decreases pressure drop, increases surface area.
d. 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
both parallel and straight
As complete saturation of an adsorbent is approached, the differential heat
of adsrop-tion approaches
a. that of normal condensation.
b. integral heat of adsorption.
c. zero.
d. none of these.
that of normal condensation
‘Absorption with chemical reaction’ is involved in the removal of
a. carbon dioxide from gaseous stream using alkaline solution.
b. benzol from coke oven gas using solar oil/wash oil.
c. ammonia from coke oven gas using refrigerated water.
d. 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
> 1
Pick out the wrong statement:
a. Reboiler is not used in open steam distillation.
b. The separation of solutes of different molecular sizes in a liquid
solution by use of a suitable membrane is called dialysis.
c. Freeze drying is used for the drying of fish.
d. 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.
heated cylinder
Pick out the wrong statement.
a. Critical moisture content is not a property of the material itself.
b. A sharp increase in pressure drop gives an indication of the
flooding in a distillation column.
c. Separation of components is not possible in liquid extraction, if
selectivity is unity.
d. 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
a. large latent heat
b. low viscosity
c. small latent heat
d. none of these
large latent heat
The most common packing used in industrial operations is __________
rings.
raschig
When the feed to a distillation column is a saturated liquid, slope of the
feed line is
infinity
Leaching of sugar from sugar beets is done by
hot water
Absorption factor method is used to calculate the number of ideal stages,
when
a. operating line lies above the equilibrium line.
b. operating line lies below the equilibrium line.
c. both operating and equilibrium lines are parallel.
d. pressure drop in the column is very high
both operating and equilibrium lines are parallel.
Flights in a rotary dryer are provided to
a. lift and shower the solids thus exposing it thoroughly to the drying
action of the gas.
b. reduce the residence time of solid.
c. increase the residence time of the solid.
d. none of these
lift and shower the solids thus exposing it thoroughly to the drying
action of the gas.
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
a. the system comprises of partially mis-cible liquids.
b. the system comprises of miscible liquids.
c. the system comprises of an azeotrope.
d. 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
a. degree of dispersion of one fluid in the other.
b. interfacial surface exposed between the phases.
c. both (a) & (b).
d. 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
a. 0.0
a. 0.2
b. 0.4
c. 1.0
0.4
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
a. 0.60
b. 0.24
c. 1
d. 0.72
1
The reciprocal of stripping factor is termed as
a. selectivity index
b. relative volatility
c. absorption factor
d. Murphree efficiency
absorption factor
Ponchan-Savarit method analyses the fractional equipment based on
a. enthalpy balance only.
b. material balance only.
c. both enthalpy and material balances.
d. the assumption of constant molaloverflow.
both enthalpy and material balances
Percentage saturation is __________ the relative saturation.
a. always smaller than
b. always greater than
c. not related to
d. none of these
always smaller than
In case of a desorber (stripper), the
a. operating line always lies above the equilibrium curve.
b. operating line always lies below the equilibrium curve.
c. temperature remains unaffected.
d. temperature always increases.
operating line always lies below the equilibrium curve.
What is the reflux ratio at total reflux?
a. Zero
b. Infinity
c. Unity
d. Data insufficient
infinity
Under conditions of flooding in packed tower, the gas pressure drop
a. decreases rapidly
b. increases rapidly
c. remains constant
d. is maximum
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).
a. 1-5
b. 10-60
c. 200-300
d. 500
10-60
For absorbing a sparingly soluble gas in a liquid
a. gas side mass transfer co-efficient should be increased.
b. liquid side mass transfer co-efficient should be increased.
c. liquid side mass transfer co-efficient should be decreased.
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
The minimum number of theoretical plates is required for achieving a
given separation in distillation column with
total reflux
A good solvent used for absorption should not have very high
a. viscosity
b. vapor pressure
c. freezing point
d. all (a), (b) & (c)
all a b c
In a counter-current liquid extractor
a. both liquids flow at fixed rate.
b. both liquids can have any desired flow rate.
c. only one of the liquids may be pumped at any desired rate.
d. 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
?
a. Low vapour pressure
b. Low velocity
c. Low freezing point
d. None of these
none of these
The wetted wall tower is used to determine
a. individual mass transfer co-efficient (M.T.C.) in gaseous system.
b. M.T.C. of individual components in a liquid-liquid system.
c. M.T.C. of liquid in liquid-gas system.
d. 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
a. less
b. more
c. same
d. unpredictable
less
Positive deviation from Raoult’s law means a mixture whose total pressure
is
a. greater than that computed for ideality.
b. less than that computed for ideality.
c. less than the sum of the vapour pressure of the components.
d. 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
a. increases
b. decreases
c. decreases linearly
d. remains unaffected
increases
Prandtl number for water at 20°C is about
7
Boiling point diagram is
a. not affected by pressure.
b. affected by pressure.
c. a plot of temperature vs. liquid composition.
d. 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,
a. as the acetone concentration increases, the solubility curves
approach each other.
b. both the phases become identical at a particular common point on
both the solubility curves called the plait point.
c. 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.
d. all (a), (b) and (c).
all a b c
Steam distillation is used to
a. reduce the number of plates.
b. avoid thermal decomposition of a component.
c. increase the efficiency of separation.
d. increase the total pressure of distillation.
avoid thermal decomposition of a component
Freundlich equation applies to the adsorption of solute from
a. dilute solutions, over a small concentration range.
b. gaseous solutions at high pressure.
c. concentrated solutions.
d. 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.
a. no change in theoretical
b. marginal decrease in the number of
c. major decrease in the number of
d. none of these
marginal decrease in the number of
The apex of an equilateral-triangular coordinate (in ternary liquid system)
represents a/an
a. pure component
b. binary mixture
c. ternary mixture
d. insoluble binary system
pure component
A slurry is to be dried to produce flaky solid. Which dryer would you
recommend ?
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 ?
a. Cooling and dehumidification.
b. Heating and dehumidification at almost constant wet bulb
temperature.
c. Dehumidification with dry bulb temperature remaining constant.
d. None of these.
Heating and dehumidification at almost constant wet bulb
temperature.
In gas-liquid contact operation, the number of ideal stages, . This is true
when the stripping factor ‘S’ is
s>1
The cooling effect in a cooling tower can not be increased by
a. increasing the air velocity over the wet surfaces.
b. reducing the humidity of entering air.
c. lowering the barometric pressure.
d. none of these.
none of these
The value of NA/(NA + NB) for steady state molecular diffusion of gas ‘A’
through non-diffusing gas ‘B’ is
1
Pick out the wrong statement
a. Co-current absorbers are usually used, when the gas to be
dissolved in the liquid is a pure substance.
b. In case of gas absorption, HETP is equal to HTU, when both the
operating line & the equilibrium lines are parallel.
c. Hatta number is important in case of gas absorption with chemical
reaction.
d. In actual practice, absorption is an en-dothermic process, while
stripping is an exothermic process
d. In actual practice, absorption is an en-dothermic process, while
stripping is an exothermic process
- When the mixture to be distilled has a very high boiling point and the
product material is heat sensitive, the separation technique to be used is
__________ distillation.
steam
Large scale drying of wheat is done in a __________ dryer.
spouted
Azeotropic distillation is employed to separate
a. constant boiling mixture.
b. high boiling mixture.
c. mixture with very high relative volatility.
d. heat sensitive materials.
constant boiling mixture
The drying time between fixed moisture content within diffusion
controlled ‘falling rate period’ is proportional to (assuming that drying occurs
from all surfaces of the solid) (where, T = thickness of the solid )
T^2
At the boiling point of the liquid at the prevailing pressure, the saturated
absolute humidity becomes
INFINITY
Pressure drop through plate tower as compared to that through packed
tower, for the same duty will be
MORE
Dimension of mass diffusivity is the same as that of
KINEMATIC VISCOSITY
Steam distillation is used to separate
a. azeotropes.
b. high boiling substances from nonvolatile impurities.
c. heat sensitive materials.
d. mixtures of low relative volatility.
HIGH BOILING substances from nonvolatile impurities
. Dorr thickener is an equipment used for
SEDIMENTATION
. In distillation where q is defined as the moles of liquid flow in the
stripping section per mole of feed introduced, for saturated liquid feed
q=1
Which of the following is an undesirable property in a tower packing ?
a. Large surface per unit volume.
b. Large free cross-section.
c. Low weight per unit volume.
d. Large weight of liquid retained.
large weight of liquid retained
Water entrained by circulating air in cooling towers is termed as
drift
A 25 cm x 25 cm x 1 cm flat sheet weighing 1.2 kg initially was dried
from both sides under constant drying rate conditions. It took 1500 seconds
for the weight of the sheet to reduce to 1.05 kg. Another 1m x 1m x 1cm flat
sheet of the same material is to be dried from one side only.Under the same
constant drying rate conditions, the time required for drying (in seconds) from
its initial weight of 19.2 kg to 17.6 kg is
1000
With increase in temperature, the rate of leaching increases, because the
a. diffusivity of solute increases.
b. viscosity of solvent decreases.
c. thermal conductivity of solute increases.
d. none of these.
diffusivity of solute increases
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
The Kundsen diffusivity is proportional to (where, T = absolute
temperature)
T1/2
In an absorption coloumn, the flooding velocity for random packing is
__________ that for stacked/regular packing.
a. greater than
b. smaller than
c. equal to
d. either (a), or (b) ; depends on the type of packing
SMALLER THAN
The relation among various mass transfer co-efficients (M.T.C) for ideal
gases is given by (where, Kc & Km are M.T.C. for equimolar counter
diffusion with concentration & mole fraction respectively as the driving force.
and, Kp = M.T.C. for diffusion of a gas through a stagnant inert gas with
pressure as driving force.)
a. Kc = Kp = Km
b. Kc = Kp/RT = Km . RT/P
c. Kc = Kp . RT = Km . RT/p
d. none of these
Kc = Kp . RT = Km . RT/p
Leaching of uranium ore and gold ore is done in
Pachuka tanks
Blowdown in a cooling tower
a. means discarding a small fraction of circulating water to prevent
and limit the concentration of salt and impurities.
b. increases the scale forming tendencies of water.
c. is undesirable.
d. all (a), (b) & (c).
means discarding a small fraction of circulating water to prevent
and limit the concentration of salt and impurities.
Antibiotics are best handled in a
a. Podbielniak extractor.
b. sieve tray contractor.
c. rotating disc contactor.
d. pulsed column extractor.
Podbielniak extractor.
The fixed cost of a distillation column at minimum reflux ratio is
infinite
_________ extractor uses centrifugal force for separating the two phases.
a. Treybal
b. Schiebel
c. Podbielniak
d. None of these
Podbielnniak
a. Mechanical agitation is required, if the system has low interfacial
tension.
b. Seive tray towers are generally used for systems having low
interfacial tension.
c. When Henry’s law constant is very small, then the mass transfer
rate is controlled by the gas film resistance.
d. Taylor-Prandtl analogy for heat and mass transfer considers the
transfer through both laminar and turbulent layers.
mechanical agitation is required
Acetic acid will be most economically separated from a dilute solution of
acetic acid in water by
a. solvent extraction
b. continuous distillation
c. evaporation
d. absorption
Solvent extraction
Design calculation for multiple component distillation is done by
a. Ponchon-Savarit method
b. Mccabe-Thiele method
c. enthalpy concentration method
d. tray to tray calculations.
tray to tray calculations
To get high tray efficiency
a. interfacial surface between liquid and gas phase should be large.
b. time of contact between the two phases should be less.
c. gas velocity should be very low.
d. liquid entrainment should be severe.
interfacial surface between liquid and gas phase should be large.
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
a. D/a
b. D/2a
c. proportional to D
d. dependent on the Reynolds number
dependent on the Reynolds number
Pick out the wrong statement. Generally for physical adsorption, a gas of
a. higher molecular weight is adsorbed in preference to a gas of low
molecular weight.
b. high critical temperature is adsorbed in preference to a gas of low
critical temperature.
c. low volatility is adsorbed in preference to a gas of high volatility.
d. none of these.
none of these
In most of the mechanically agitated liquid-liquid extractors, baffles or
horizontal compartmental plates are provided, which helps in
a. reducing the axial mixing.
b. increasing the rate of extraction.
c. maintaining the concentration difference between the two phases.
d. all ‘a’, ‘b’ & ‘c’.
all a b c
Solvent extraction is the terminology applied to the liquid-liquid extraction,
which is preferred for the separation of the components of liquids, when
a. extracting solvent is cheaply & abundantly available.
b. one of the liquid components is heat sensitive.
c. viscosity of liquid components is very high.
d. one of the liquid components has very high affinity towards the
solvent
d. one of the liquid components has very high affinity towards the
solvent
Inside the distillation column, the
a. driving force for the vapour flow is the pressure drop.
b. liquids are not always at their bubble points.
c. pressure increases gradually from bottom to the top of the column.
d. none of these
driving force for the vapour flow is the pressure drop.
. Occurrence of ‘case hardening’ during drying of a high moisture solid cake
__________ the drying rate.
a. increases
b. decreases
c. does not affect
d. exponentially increases
decreases
Which of the following is not a continuous drier ?
tray drier
Humidification involves mass transfer between a pure liquid phase and a
fixed gas, which is
insoluble in the liquid
__________ is the temperature at which a gas-vapor mixture becomes
saturated, when cooled at constant total pressure out of contact with a liquid.
dew point
Rate of leaching increases with increasing
a. temperature
b. viscosity of solvent
c. pressure
d. size of the solid
temperature
An azeotropic mixture is a __________ mixture.
a. binary
b. ternary
c. constant boiling point
d. none of these
CONSTANT BOILING POINT
Pick out the wrong statement.
a. In the McCabe-Thiele diagram for binary distillation, vertical feed
line represents saturated liquid feed and horizontal feed line
represents saturated vapour feed.
b. In small columns, local efficiency is larger than Murphree
efficiency; in large columns local efficiency is smaller than
Murphree efficiency.
c. For Laminar flow over a plate of length L, the local mass transfer
co-efficient at a distance L from the leading edge is 1.5 x 10-2m/s.
Then the average mass transfer co-efficient for the plate is 2 x 10
2m/s.
d. The concentration and hydrodynamic boundary layers over a flat
plate are of equal thickness, if Schmidt number is equal to unity.
c. For Laminar flow over a plate of length L, the local mass transfer
co-efficient at a distance L from the leading edge is 1.5 x 10-2m/s.
Then the average mass transfer co-efficient for the plate is 2 x 10
2m/s.
Molecular seives are regenerated by heating to __________ °C.
200-330
In a counter-current extractor, as the axial mixing increases, the extraction
efficiency
DECREASES
Heat sensitive materials like certain pharmaceuticals and food stuffs can
be dried in a/an __________ dryer.
FREEZE
In extractive distillation, solvent is
a. added to alter the relative volatility of the mixture.
b. of high volatility.
c. present in overhead stream.
d. of high viscosity to give high tray efficiency.
added to alter the relative volatility of the mixture.
Radioactive nuclear waste is treated in
a. mixer-settler extractor
b. rotating-disc contactor
c. pulsed column extractor
d. Bollman extractor
PULSED COLUMN
Large scale drying of sugar is done in a __________ dryer.
a. spouted bed
b. tray
c. rotary
d. truck
ROTARY
________ temperature is the steady state temperature attained by a
small amount of liquid evaporating into a large quantity of unsaturated gas
vapor mixture.
WETBULB
The drying time between fixed moisture contents within the ‘constant rate
period’ is proportional to (assuming that drying occurs from all surfaces of the
solid) (where, T = thickness of the solid )
T
equation applies to diffusivities in liquids.
GILLILAND
A packed tower compared to a plate tower for a particular mass transfer
operation
a. incurs smaller pressure drop.
b. allows installation of cooling coils.
c. is less costly when built in large sizes/diameters.
d. is more suitable, if suspended solids are present in fluid streams
INCURS SMALLER PRESSURE DROP
Which of the following is the most commonly used leaching solvent in
vegetable oil industry ?
a. Phenol
b. Hexane
c. Furfurol
d. Liquid SO2
HEXANE
In an absorber, HETP does not vary with the
a. flow rate of liquid
b. flow rate of gas
c. type and size of packing
d. none of these
NONE
Large quantity of silica gel is normally dried in a __________ dryer.
THROUGH CIRCULATION
For the same system, if the same liquid used in an absorber is decreased,
the tower height will
INCREASE
Hydrogenation of oil is carried out in a/an __________ in Vanaspati
manufacturing plant.
AGITATED VESSEL
Sides of equilateral-triangular co-ordinates (on which ternary liquid
system is plotted) represent
BINARY MIXTURE
In distillation column design, the McCabe-Thiele procedure is inadequate
and a Ponchan-Savarit procedure is needed, when
a. saturated feed is not used.
b. an azeotrope forms.
c. the latent heat of vaporisation of the more and less volatile
components are greatly different.
d. a total condenser is used.
TOTAL CONDENSER IS USED
In an interphase mass transfer process, the lesser the solubility of a given
solute in a liquid, the higher are the chances that the transfer process will be
a. liquid phase resistance-controlled.
b. gas phase resistance controlled.
c. impossible.
d. driven by a non-linear driving force.
GAS PHASE RESISTANCE CONTROLLED
As the reflux ratio decreases, the
a. separation becomes more efficient.
b. number of plates increases.
c. column diameter increases.
d. none of these.
NUMBER OF PLATES INCREASES
Which of the following equipments is not used for gas dispersion ?
a. Agitated vessels
b. Bubble cap tray towers
c. Perforated sieve tray towers
d. Spray towers
SPRAY TOWERS
One mole feed of a binary mixture of a given composition is flash
vaporised at a fixed P and T. If Raoult’s law is obeyed, then changing the feed
composition would effect
a. the product composition but not the fraction vaporised.
b. the product composition as well as the fraction vaporised.
c. the fraction vaporised but not the product composition.
d. neither the product composition nor the fraction vaporised.
the fraction vaporised but not the product composition.
With increase in the liquid flow rate at a fixed gas velocity in a randomly
packed counter current gas-liquid absorption column, the gas pressure drop
a. decreases
b. remains unchanged
c. increases
d. decreases exponentially
INCREASES
Which of these columns incurs the lowest pressure drop ?
a. Packed column (with stacked packing)
b. Packed column (with dumped packing)
c. Bubble plate column
d. Pulse column
PACKED COLUMN (WITH STACKED PACKING)
If G = insoluble gas in gas stream and L = non-volatile solvent in liquid
stream, then the slope of the operating line for the absorber is
a. L/G
b. G/L
c. always < 1
d. none of these
L/G
Which of the following remains constant during evaporative cooling
process with recirculated water supply ?
WET BULB TEMPERATURE
. For stripping of a gas in a counter current stripper, the operating line
a. lies above the equilibrium curve.
b. lies below the equilibrium curve.
c. can lie above or below the equilibrium curve.
d. is always parallel to the equilibrium curve.
can lie above or below the equilibrium curve.
Which of the following same diameter columns gives lowest pressure drop
per unit height ?
a. Bubble-cap column
b. Sieve-plate column
c. Packed column (stacked)
d. Randomly packed column
PACKED COLUMN (sTACKED)
Operating velocity in a packed tower is usually __________ the flooding
velocity.
HALF
The Knudsen diffusivity is dependent on the
a. molecular velocity only.
b. pore radius of the catalyst only.
c. molecular mean free path only.
d. molecular velocity and por radius of the catalyst.
molecular velocity and por radius of the catalyst.
Minimum possible diameter of a packed coloumn is decided mainly
FLOODING
Solvent used in extractive distillation
a. is of low volatility.
b. forms a low boiling azeotrope.
c. forms a high boiling azeotrope.
d. does not alter the relative volatility of the original components.
forms a low boiling azeotrope.
The cooling effect in a cooling tower can be speeded up by
a. increasing the air velocity and area of exposed wet surface.
b. reducing the barometric pressure.
c. reducing the humidity of the air.
d. all (a), (b) and (c)
ALL A B C
When both the fluids flow concurrently in an absorber, the slope of the
operating line is
a. - ve
b. + ve
c. 1
d. -1
-VE
The percentage humidity is less than the relative humidity only at
__________ percent humidity.
a. zero
b. hundred
c. both zero and hundred
d. none of these
BOTH ZERO AND HUNDRED
Back-trapping in a distillation column
a. increases tray efficiency.
b. decreases tray efficiency.
c. reduces pressure drop.
d. is desirable, as it provides improved vapour-liquid contact.
DECREASES TRAY EFFICIENCY
Flooding in a vapor-liquid contacting equipment occurs in a tray, when the
pressure drop through a tray is __________ the liquid head available in the
downcomer.
MORE THAN
Milk is dried usually in a __________ dryer.
SPRAY
At a given equilibrium pressure, with increase in temperature, the
concentration of adsorbed gas on solid adsorbant
DECREASES
Which of the following adsorbent is used to decolourise yellow glycerine ?
a. Silica gel
b. Alumina
c. Fuller’s earth
d. Activated carbon
ACTIVATED CARBON
In a distillation column, with increase in the reflux ratio, the heat removed
in the cooler
INCREASES
Pick out the wrong statement.
a. Constant pressure distillation can not separate an azeotropic
mixture.
b. Relative volatility of a binary mixture changes appreciably with the
minor change in temperature.
c. The relative volatility of a binary mixture at azeotropic
composition is unity.
d. Flash distillation is practised on wide spread scale in petroleum
refinery.
Relative volatility of a binary mixture changes appreciably with the
minor change in temperature.
The falling rate period in the drying of a solid is characterised by
a. increase in rate of drying.
b. increasing temperatures both on the surface and within the solid.
c. decreasing temperatures.
d. none of these.
ncreasing temperatures both on the surface and within the solid.
In which of the following unit operations, the selectivity is an important
parameter
SOLVENT EXTRACTION
Which of the following is an undesirable characteristic for the solvent used
in gas absorption ?
a. Low vapor pressure
b. Low viscosity
c. High gas solubility
d. None of these
NONE OF THESE
Which of the following equipments is not used for liquid dispersion ?
a. Wetted wall towers
b. Packed towers
c. Venturi scrubbers
d. Agitated vessels
AGITATED VESSELS
Diameter of raschig rings used in packed tower in industry is normally
around __________ inches.
a. 2
b. 8
c. 12
d. 18
2
The diffusion co-efficient in m2 /s. of acetic acid in benzene (liquid in
liquid) is
a. 2.09 x 10-4
b. 2.09 x 10-5
c. 2.09 x 10-9
d. 2.09 x 10-12
2.09 x 10-9
. Pick out the wrong statement.
a. The Reynolds analogy for mass transfer is given by Lewis relation
and is applicable, when Schmidt number is one.
b. Sherwood number for flow in pipes can be expressed as the ratio of
the concentration gradient at wall to the overall concentration
difference.
c. According to film theory for equimolar counter diffusion, the mass
transfer coefficient is given by DAB(b)P - 3, Q - 2
d. The z-component of the total mass flux of a component A in binary
mixture of A and B is given by - Dab’.dCA/dz.
c. According to film theory for equimolar counter diffusion, the mass
transfer coefficient is given by DAB(b)P - 3, Q - 2
. In case of non-ideal gases and liquids, the molal diffusivity
a. varies inversely as the pressure.
b. varies directly as the pressure.
c. is independent of pressure.
d. is equal to the volumetric diffusivity.
INDEPENDENT OF PRESSURE
. Condensation of a vapour-gas mixture just begins, when (where, p =
partial pressure of the vapour P = vapour pressure of the liquid )
a. p = P
b. p»_space;P
c. p < P
d. p «_space;P
p=P
__________ number indicates the ratio of the rates of the heat and mass
transfer incase of a cooling tower.
LEWIS
The expression, y(1 - x)/x(1 - y) is for
RELATIVE VOLATILITY
In physical terms, Schmidt number means
a. thermal diffusivity/mass diffusivity.
b. thermal diffusivity/momentum diffusivity.
c. momentum diffusivity/mass diffusivity.
d. mass diffusivity/thermal diffusivity.
momentum diffusivity/mass diffusivity.
. In case of liquids, the binary diffusivity is proportional to (where, T =
temperature)
a. T
b. T1/2
c. T2
d. 1/T
T
. The diffusivity, DAB (for component A diffusing in B) is equal to the
diffusivity DBA (for component B diffusing in A) for a binary mixture of
IDEAL GASES
Mass transfer co-efficient is directly proportional to DAB0.5, according to
__________ theory.
a. penetration
Sand is dried in foundaries in a___drier.
FLUIDIZED
Which of the following employs an accessory known as ‘drift eliminator’ ?
a. Multiple effect evaporator.
b. Mechanical draft cooling tower.
c. Rotary dryer.
d. Rotating disc contactor.
MECHANICAL DRAFT COOLING TOWER
. Pick out the correct statement.
a. Higher hold up of the solid in the rotary dryer results in better
exposure of the solids to the gas.
b. The ‘Hatta number’ is important in problems involving gas
absorption without chemical reaction.
c. For a non-reacting binary mixture of ideal gases, the partial
pressure distribution of both components is linear in the case of
steady state equimolal counter-diffusion.
d. Total reflux in case of distillation operation requires infinite
number of plates for a binary system separation.
For a non-reacting binary mixture of ideal gases, the partial
pressure distribution of both components is linear in the case of
steady state equimolal counter-diffusion.
. Pick out the correct statement.
a. For identical gas flow rates, less pressure drop occurs through a
plate tower than through a packed tower.
b. 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.
c. For the same duty, plate columns weigh less than packed columns.
d. all (a), (b) and (c).
ALL A B C
. Humid volume is the total volume in m3 of 1 kg of
a. vapour laden gas at 1 atm. and room temperature.
b. gas plus its accompanying vapour at 1 atm. and room temperature.
c. gas plus its accompanying vapour at 1 atm. and gas temperature.
d. vapour laden gas at 1 atm. and gas temperature.
gas plus its accompanying vapour at 1 atm. and gas temperature.
Diameter to height ratio for a rashig ring is
a. 1
b. 0.5
c. 2
d. 8
1
. The equipment used in the extraction of highly corrosive radio active
liquids is
PULSE COLUMN
Advantage of continuous drying over batch drying is that the
a. drying cost per unit weight of dried product is less.
b. product with more uniform moisture content is produced.
c. equipment size required is smaller.
d. all ‘a’, ‘b’ & ‘c’
ALL A B C
With increase in temperature, the rate of extraction in leaching (solid
liquid extraction system)
a. increases
b. decreases
c. remains unaffected
d. increases Linearly
INCREASES
- In a packed bed absorption column, the channelling will be noted by the
a. increase in flow rate.
b. sharp drop in pressure drop.
c. sharp rise in pressure drop.
d. none of these.
sharp drop in pressure drop.
Gaseous diffusivity at atmospheric pressure is of the order of __________
cm2/second.
a. 1
b. 1 to 5
c. 5 to 10
d. 10
1
In liquid-liquid extraction, the number of phases at plait point is
a. 1
b. 2
c. 3
d. 4
1
. In a liquid-liquid extraction, 10 kg of a solution containing 2 kg of solute
C and 8 kg of solvent A is brought into contact with 10 kg of solvent B.
Solvent A and B are completely immiscible in each other whereas solute C is
soluble in both the solvents. The extraction process attains equilibrium. The
equilibrium relationship between the two phases is Y* = 0.9X, where Y* is
the kg of C/kg of B and X is kg of C/kg of A. Choose the correct answer.
a. The entire amount of C is transferred to solvent B.
b. Less than 2 kg but more than 1 kg of C is transferred to solvent B.
c. Less than 1 kg of C is transferred to B.
d. No amount of C is tranferred to B.
The entire amount of C is transferred to solvent B.
he surface renewal frequency in Danckwerts’ model of mass transfer is
given by (KL: mass transfer co-efficient)
a. (KL2.DA)1/2
b. KL2.DA
c. KL2/DA
d. KL/DA2
(KL2.DA)1/2
If Rm is the minimum reflux ratio, the optimum reflux ratio may be
around __________ Rm.
a. 1.2 to 1.5
b. 2.5 to 3
c. 3 to 4
d. 5
1.2 TO 1.5
During dehumidification of unsaturated air wet bulb temperature & partial
pressure of vapor are not constant. However, during evaporative cooling
process with recirculated water supply, the __________ remains constant.
a. wet bulb temperature
b. partial pressure of water vapor
c. relative humidity
d. none of thes
WET BULBL TEMPERATURE
In case of absorption, both the operating and equilibrium lines will be
straight for
a. isothermal operation.
b. dilute solutions.
c. dilute solutions and isothermal operation.
d. none of these.
dilute solutions and isothermal operation.
Mass transfer co-efficient varies as DAB0.5, according to the __________
theory
SURFACE RENEWAL
For an absorber, both equilibrium and operating line will be straight for
a. concentrated solution and non-isothermal operation.
b. dilute solution and non-isothermal operation.
c. dilute solution and isothermal operation.
d. concentrated solution and isothermal operation.
c. dilute solution and isothermal operation.
In the figure xF, xD and xW represent the weight fraction of benzene in the
feed, distillate and residue respectively. The reflux ratio is
0.6
Unsaturated air (with dry bulb and wet bulb temperatures being 45°C and
25°C respectively) is passed through a water spray chamber maintained at
23°C. The air will be cooled and
a. humidified with wet bulb temperature decreasing.
b. humidified at constant wet bulb temperature.
c. dehumidified.
d. none of these
humidified with wet bulb temperature decreasing.
Humid volume, at a given temperature is a/an __________ function of
humidity.
LINEAR
The Schmidt number which is defined as, μ/ρ D, is the ratio of the
a. momentum diffusivity to the mass dif-fusivity.
b. thermal diffusivity to the mass diffusivity.
c. momentum diffusivity to the thermal diffusivity.
d. none of these.
momentum diffusivity to the mass dif-fusivity
. If f is defined as above, then which of the following applies to a feed at
dew point ?
f=1
Perforated plate towers are unique for solvent extraction because, they
provide
a. higher contact area.
b. better contact of the phase.
c. repeated coalescence & redispersion of the drop phase.
d. none of these.
repeated coalescence & redispersion of the drop phase.
In case of absorption & stripping, the interface of the liquid & gas phases
are present in equilibrium, when the diffusional resistance of __________ is
zero.
a. interface
b. gas phase
c. liquid phase
d. all ‘a’, ‘b’ & ‘c’
interface
Pick out the wrong statement pertaining to the analogy between equations
of heat and mass transfer operations.
a. Sherwood number in mass transfer is analogous to Nusselt number
in heat transfer.
b. Prandtl number in heat transfer is analogous to Schmidt number in
mass transfer.
c. Reynolds number in mass transfer is analogous to Grashoff number
in heat transfer.
d. Reynolds number remains the same in both heat and mass transfer.
Reynolds number in mass transfer is analogous to Grashoff number
in heat transfer.
The slope of the operating line for a single component co-current absorber
when plotted in terms of mole ratio units is
a. 0
b. ∞
c. -ve
d. +ve
-ve
The individual mass transfer co-efficients (moles/m2 . s) for absorption of a
solute from a gas mixture into a liquid solvent are, KL = 4.5 and KG = 1.5.
The slope of the equilibrium line is 3. Which of the following resistance (s) is
(are) controlling ?
a. liquid side
b. gas side
c. interfacial
d. both liquid and gas side
gas side
Pore size of the molecular seive 5A is __________ mm.
a. 5
b. 0.5
c. 0.05
d. 50
0.5
Swenson-Walker crystalliser is a __________ unit
a. continuous
b. batch
c. semi-batch
d. cooling (adiabatic)-cum-evaporation
continuous
According to the Fenske equation, what will be the minimum number of
plates required in a distillation column to separate an equimolar binary
mixture of components A and B into an overhead fraction containing 99 mol%
A and a bottom fraction containing 98 mol% B ? Assume that relative
volatility (αAB = 2) does not change appreciably in the coloumn.
a. 5
b. 9
c. 12
d. 28
12
Absorption (liquid-gas system) with evolution of heat as compared to
isothermal absorption results in
a. decreased solute solubility.
b. large minimum liquid to gas (L/G) ratio.
c. large number of trays.
d. all (a), (b) and (c).
all a b c
With increase in temperature, the mutual solubility of two liquids
a. increases
b. decreases
c. remains unchanged
d. decreases exponentially
increases
Pick out the wrong statement.
a. In solvent extraction, the distribution co-efficient should be as
large as possible for solvent economy.
b. With increase in pressure, the solubility of gases in solvent
increases at a fixed temperature.
c. Decrease in Murphree plate efficiency is an indication of
entrainment in distillation coloumn.
d. The capacity of a distillation coloumn is maximum at total reflux.
The capacity of a distillation coloumn is maximum at total reflux.
The relative volatility of a binary mixture at the azeotropic composition is
1
Relative volatility varies with the concentration of component for an ideal
solution. The relative volatity of a binary mixture may be defined as the ratio
of vapor pressure of component ‘A’ to that of component ‘B’, when
a. only vapor phase follows Raoult’s law.
b. only liquid phase obeys Dalton’s law.
c. liquid phase obeys Dalton’s law and vapor phase obeys Raoult’s
law.
d. Vapor phase obeys Dalton’s law and liquid phase obeys Raoult’s
law.
Vapor phase obeys Dalton’s law and liquid phase obeys Raoult’s
law.
Bound moisture is that liquid which exerts an equilibrium vapor pressure
__________ that of the pure liquid at the given temperature.
a. less than
b. more than
c. equal to
d. either (o) or (b); depends on the solid
less than
Lewis number (Le) is
a. Sc / Pr
b. Pr x St
c. Sh x Pr
d. St x Sh
Sc/Pr
Which of the following is not a continuous leaching equipment ?
a. Pachuka tank
b. Kennedy extractor
c. Bollman extractor
d. Hydrocyclones
Pachuka tanks
__________ extractor is used for the concentration of radioactive nuclear
waste.
Pulsed column
Moisture content of a substance when at equilibrium with a given partial
pressure of the vapour is called the __________ moisture.
equilibrium
All moisture in a non-hygroscopic material is the __________ moisture.
unbound
Pick out the correct relationship. (where, Ri = internal reflux ratio Ro =
external reflux ratio. )
a. (1 + Ro) = Ro/Ri
b. (1 - Ro) = Ro/Ri
c. (1 + Ri) = Ro/Ri
d. (1 - Ri) = Ro/Ri
(1 + Ro) = Ro/Ri
Separation of __________ employs gaseous diffusion process.
a. N2 and O2 from air
b. isotopes of uranium
c. isotopes of helium
d. SO2 and air
isotopes of uranium
For water-ethanol system, the minimum reflux ratio
a. is computed from the slope of the upper operating line that is
tangent to the equilibrium curve.
b. is computed from the intercept of the operating line.
c. cannot be computed.
d. is the optimum reflux ratio.
is computed from the slope of the upper operating line that is
tangent to the equilibrium curve.
The interfacial area per unit volume of dispersion, in a gas-liquid
contactor, for fractional hold up of gas = 0.1 and gas bubble diameter = 0.5
mm is given by (in m2/m3)
a. 500
b. 1200
c. 900
d. 800
500
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
Experimental determination of __________ is done by wetted wall column
method.
a. diffusion co-efficient
b. mass transfer co-efficient
c. NTU
d. none of these
mass trasnfer coefficient
Pick out the wrong statement:
a. Absorption factor is constant, when the equilibrium and operating
lines are straight.
b. In case of a stripper, the equilibrium curve is always below the
operating line.
c. In case of an absorber, the operating line is always above the
equilibrium curve.
d. In the absorption of low solubility gases, the liquid film is the
controlling resistance.
In case of a stripper, the equilibrium curve is always below the
operating line.
In liquid extraction, if the selectivity is unity, then
a. separation of the constituents is the most effective.
b. no separation will occur.
c. amount of solvent required will be minimum.
d. solvent flow rate should be very low.
no separation will occur
Paper industry employs __________ driers.
cylinder
Which of the following has the same dimension as mass diffusivity ?
a. Momentum flux
b. Kinematic viscosity
c. Thermal diffusivity
d. Both (b) and (c)
kinematic viscosity
Pick out the wrong statement pertaining to the cooling towers.
a. In case of induced draft cooling tower, the fan is placed at the top
of the tower.
b. Effectiveness of forced draft cooling tower is reduced by the
recirculation of the humid and hot discharged air.
c. A natural draft cooling tower is recommended to be used, when the
air humidity is low and air temperature is also low.
d. Effectiveness of a mechanical draft cooling tower is reduced with
increase in air wet-bulb temperature.
Effectiveness of a mechanical draft cooling tower is reduced with
increase in air wet-bulb temperature.
Experiments were conducted to determine the flux of a species A in a
stagnant medium across a gas-liquid interface. The overall mass transfer co
efficient based on the liquid side for dilute systems for the above was
estimated to be 4 x 10-3 kg mole/m2.s. The equilibrium data for the system is
given as y = 2x. The flux across the interface (in kg mole/m2 .s) for bulk
concentrations of A in gas phase and liquid phase as y = 0.4 and x = 0.01
respectively is
a. 5.6 x 10-4
b. 8.5 x 10-4
c. 5.6 x 10-3
d. 8.5 x 10-3
8.5 x 10-4
Leaching of coarse solid lumps is also termed as
Percolation
The main reason for dividing a tall packed tower into series of small
towers is to
a. minimise the overall pressure drop.
b. avoid flooding.
c. reduce liquid hold up.
d. avoid channeling.
avoid channeling
Co-current absorbers are usually used when the gas to be dissolved in the
liquid is
a. sparingly soluble
b. highly soluble
c. a pure substance
d. a mixture
pure substance
At what percentage (by volume) of alcohol composition, it forms an
azeotrope with water ?
95
Measurement of the interfacial area of mass transfer is achieved easily &
accurately in case of a __________ coloumn.
a. spray
b. packed
c. bubble cap plate
d. wetted wall
wetted wall
With the lowering of equiliDrium pressure, at a given temperature, the
amount of ad-sorbate on the adsorbent
decreases
Mass transfer co-efficient is defined as
a. Flux = Co-efficient/concentration difference.
b. Co-efficient = Flux/concentration difference.
c. Flux=concentration difference/co-effi-cient.
d. none of these.
Co-efficient = Flux/concentration difference.
When an unsaturated air-water mixture is heated at constant pressure, then
a. the partial pressure of water vapour increases.
b. the specific humidity decreases.
c. The relative humidity increases.
d. The relative humidity decreases.
d. The relative humidity decreases.
At a fixed pressure, the humidity depends upon the partial pressure of
vapor in the mixture. Humidity of a vapour free gas is __________ percent.
0
In case of physical adsorption, the difference between heat of adsorption
and heat of normal condensation is
a. equal to the heat of formation of surface compound.
b. equal to the heat of wetting.
c. zero.
d. called integral heat of adsorption.
equal to the heat of wetting
Pick out the wrong statement:
a. Change in barometric pressure does not affect the relative
humidity.
b. In case of a packed tower, the operating velocity is about half of
the flooding velocity, generally.
c. ‘Elution’ means the desorption of the adsorbed solute by a solvent.
d. The equilibrium moisture content of the solid can be reduced by
increasing the absolute humidity.
The equilibrium moisture content of the solid can be reduced by
increasing the absolute humidity.
The value of L/mG ratio for economical absorption operation ranges from
a. 0.5 to 0.8
b. 0.8 to 1.2
c. 1.25 to 2.0
d. 2.5 to 3.5
1,25 to 2
Large scale usage of flash distillation is practised in
a. soap manufacturing
b. ammonia synthesis plant
c. polymerisation industry
d. petroleum refining
petroleum refining
High pressure at the bottom of a distillation tower handling heat sensitive
materials results in
a. thermal decomposition of bottoms.
b. increased relative volatility.
c. erosion of the tower.
d. very efficient operation
thermal decomposition of bottoms.
Alcohol is dehydrated using __________ distillation.
azeotropic
Separation of two volatile liquids by distillation makes use of their
a. selectivity
b. relative volatility
c. solubility
d. density difference
relative volatility
Dried finished product sampled from various parts of a __________ dryer
exhibits non-uniformity in the moisture content.
tray
is used as an ‘entrainer’ for the separation of acetic acid-water
mixture by distillation.
Butyl acetate
Rotary dryers cannot handle __________ materials.
a. free flowing
b. dry
c. sticky
d. granular
sticky
Pick out the correct statement.
a. Diffusivity decreases with increase in temperature.
b. Diffusivity increases with increase in molecular weight.
c. Diffusivity increases with the size of the individual molecule.
d. none of these.
none
An example of elutioh is
a. separation of uranium oxide from its ore by H2SO4 in a Pachuca
tank.
b. separation of sugar from sugar beet by hot water.
c. dissolution of tannin out of tree barks by water.
d. recovery of vegetable oils from seeds.
eparation of uranium oxide from its ore by H2SO4 in a Pachuca
tank.
The operating line for an absorber is curved, when plotted in terms of
a. mole fractions
b. mole ratios
c. partial pressure
d. mass fraction
partial pressure
Relative volatility does not change appreciably with the change in
a. temperature
b. vapour pressure of either component
c. total pressure
d. none of these
temperature
The dew point of a saturated gas phase equals the __________ temperature
gas
A solid material shows case hardening properties while drying. Which of
the following should be controlled to control the drying process ?
a. Flow rate of inlet air
b. Relative humidity of outlet air
c. Humidity of inlet air
d. Temperature of the solid
temperature of the solid
In case of liquid-liquid binary diffusion, diffusivity of one constituent into
another is not dependent on the
a. temperature and pressure
b. concentration
c. nature of the constituents
d. none of these
none of these
For continuous drying of grannular or crystalline material, the dryer used
is the __________ dryer.
a. tunnel
b. tray
c. rotary
d. none of these
rotary
When adsorption hysteresis is observed, the desorption equilibrium
pressure is __________ that obtained by adsorption.
a. always lower than
b. always higher than
c. same as
d. dependent on the system; can be either lower or higher than
always lower than
Moisture in a substance exerting an equilibrium vapour pressure less than
that of pure liquid at the same temperature is called the __________ moisture.
bound
For a binary mixture with low relative volatility, continuous rectification
to get pure products will require
a. low reflux ratio
b. less number of trays
c. small cross-section column
d. high reflux ratio
high reflux ratio
Detergent solution is dried to a powder in a
a. spray dryer
b. spouted bed dryer
c. tunnel dryer
d. pan open to atmosphere
spray
Which of the following mixtures does not form an azeotrope at atmosheric
pressure?
a. Water-alcohol
b. Methyl alcohol-acetone
c. Butyl acetate-water
d. None of these
none of these
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
a. gas film
b. liquid film
c. liquid-gas interface
d. none of these
liquid film
The overall mass transfer co-efficient for the absorption of SO2 in air with
dilute NaOH solution can be increased substantially by
a. increasing the gas film co-efficient.
b. increasing the liquid film co-efficient.
c. increasing the total pressure.
d. decreasing the total pressure.
increasing the gas film co-efficient.
Flooding results in
a. high tray efficiency
b. low tray efficiency
c. high gas velocity
d. good contact between the fluids
low tray efficiency
. For the air water system under ambient conditions, the adiabatic saturation
temperature and the wet bulb temperature are nearly equal, because
a. water has a high latent heat of evaporation.
b. Lewis number is close to unity.
c. they are always equal under all circumstances.
d. solubility of the components of air in water is very small.
water has a high latent heat of evaporation.
In an operating distillation column, the
a. vapors and liquids are at their dew point and bubble point
respectively
b. driving force for the liquid flow is its specific weight.
c. driving force for the vapor flow is the pressure drop, as the
pressure decreases gradually from the bottom to the top of the
column.
d. highest temperature is encountered at the top of the column.
driving force for the vapor flow is the pressure drop, as the
pressure decreases gradually from the bottom to the top of the
column.
The diffusivity (D) in a binary gas mixture is related to the temperature (T)
as
a. D ∝ T
b. D ∝ T0.5
c. D ∝ T1.5
d. D ∝ T2
D ∝ T1.5
For which of the following unit operations, Lewis number is of
significance ?
Humidification
Tray spacing in a distillation column of dia 10-12 ft. used in petroleum
refinery may be around __________ inches.
a. 5
b. 30
c. 60
d. 100
30
if a1 and a2 are the relative volatilities when the pressure in the distillation
column is 1 and 2 atm respectively. Pick out the correct statement.
a. a1 = a2
b. a1 = 2a2
c. a1 = 0.5 a2
d. none of these
none
The dimension of diffusivity is same as that of the
a. density
b. molal concentration
c. kinematic viscosity
d. velocity head
kinematic viscosity
The temperature to which a vapour gas mixture must be cooled (at varying
humidity) to become saturated is called the __________ temperature.
a. dew point
b. wet bulb
c. dry bulb
d. none of these
none of these
Entrainer used in azeotropic distillation should
a. form a low boiling azeotrope with one of the constituents of the
mixture.
b. form a new azeotrope of low relative volatility with one of the
constituents of the mixture.
c. have high latent heat of vaporisation.
d. have high viscosity to provide high tray efficiency.
form a low boiling azeotrope with one of the constituents of the
mixture.
In case of steam distillation, the steam leaving the liquid is not completely
saturated with distillate vapour, because
a. temperature is less.
b. total pressure is less.
c. mixing of steam with the material being vaporised is not so
intimate as to result in equilibrium condition.
d. saturated steam is used for steam distillation.
mixing of steam with the material being vaporised is not so
intimate as to result in equilibrium condition.
Pick out the wrong statement.
a. The operating line always lies above the equilibrium solubility
curve in case of a single component absorber.
b. The operating line always lies below the equilibrium solubility
curve in case of a single component stripper.
c. The operating pressure in solvent extraction system should be
below vapor pressures of all components.
d. The solubility of a particular gas in ideal solution in any solvent is
always the same.
The operating pressure in solvent extraction system should be
below vapor pressures of all components.
Leaching of coffee from coffee beans is done by
hot water
During drying operation, it is easier to remove the __________ moisture.
a. equilibrium
b. critical
c. unbound
d. bound
unbound
Ion exchange process is similar to
a. absorption
b. adsorption
c. extraction
d. leaching
aDsorption
A distillation column with N plates is being operated under normal
conditions. At some point of time, the operation is shifted to total reflux
condition (i.e., no product and residue are being withdrawn and feed to the
column is stopped). At the new steady state,
a. composition of vapors and that of liquid do not vary throughout the
column.
b. reboiler load and condenser load are minimum.
c. the top and bottom compositions are unchanged with and without
total reflux.
d. the top and bottom compositions correspond to the maximum
enrichment available.
the top and bottom compositions correspond to the maximum
enrichment available.
. Dryer widely used in a textile industry is __________ dryer.
conveyor
Solvent used in extractive distillation
a. changes the relative volatility of the original components.
b. should be of high volatility.
c. should form azeotropes with the original components.
d. all (a), (b) and (c)
changes the relative volatility of the original components.
Air at a particular humidity is heated in a furnace. The new dew point
a. decreases
b. increases
c. depends on the extent of heating
d. remain unchanged
increases
The vapour pressure exerted by the moisture contained in a wet solid
depends upon the
a. nature of the moisture.
b. temperature.
c. nature of the solid.
d. all (a), (b) and (c).
all a b c
Smoke is an example of
a. solid dispersed in liquid
b. solid dispersed in gas
c. liquid dispersed in gas
d. gas dispersed in liquid
solid dispersed in gas
Which of the following adsorbant is used in the refinning of sugar ?
a. Bone charcoal
b. Wood charcoal
c. Silica gel
d. Activated clay
bone charcoal
In McCabe-Thiele method of theoretical plate calculation for a distillation
column, the operating lines of stripping and rectifying sections coincide with
the diagonal at __________ reflux.
total
Which of the following parameters remains constant during chemical
dehumidifica-tion?
a. Dry bulb temperature
b. Partial pressure of vapour
c. Wet bulb temperature
d. None of these
dry bulb temperature
Drying of a solid involves __________ transfer.
a. only heat
b. only mass
c. both heat and mass
d. none of these
both
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
he __________ of the mixture.
a. composition
b. temperature
c. total pressure
d. all (a), (b) and (c)
temperature
Which is not concerned directly with mass transfer ?
a. Schmidt number
b. Sherwood number
c. Lewis relationship
d. Froude number
Froude
Removal of __________ exemplifies an adsorption unit operation.
a. uranium from its ore
b. water from petrol
c. ammonia from coke oven gas
d. mustard oil from mustard seed
water from petrol
Can the efficiency of a plate in the distillation tower be greater than 100% ?
a. Yes
b. Normally not; but is possible if infinite number of plates are put.
c. Never
d. Yes ; if the reflux ratio is maximum.
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.
a. increases
b. decreases
c. remains same
d. increases linearly
increases
For gas absorption, low viscosity solvents are preferred, because of their
a. better flow characteristics.
b. low pumping pressure drop.
c. rapid absorption rates.
d. all (a), (b) and (c).
all a b c
To remove all the moisture from a wet solid it requires exposure to
__________ air.
a. perfectly dry
b. highly humid
c. high temperature
d. none of these
perfectly dry
The operating cost of a distillation column at minimum reflux ratio is
a. minimum
b. maximum
c. infinite
d. zero
minimum
The reflux to a distillation column is 100 moles/hr, when the overhead
product rate is 50 moles/hr. The reflux ratio is
a. 2
b. 0.5
c. 50
d. 150
2
Molecular diffusivity of a liquid
a. increases with temperature.
b. decreases with temperature.
c. may increase or decrease with temperature.
d. is independent of temperature.
increases with temperature
Henry’s law states that the
a. partial pressure of a component over a solution is proportional to
its mole fraction in the liquid.
b. partial pressure of a component over a solution is proportional to
the mole fraction in the vapour.
c. vapour pressure is equal to the product of the mole fraction and
total pressure.
d. partial pressure is equal to the product of the mole fraction and
total pressure.
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
a. caustic solution
b. dilute ammoniacal liquor
c. dilute HCl
d. ethanolamine
dilute ammoniacal liquor
Which of the following processes is not an example of adsorption applied
to gaseous separations ?
a. Recovery of valuable solvent vapors from dilute mixture with air
and other gases.
b. Dehumidification of air and gas.
c. Removal of objectionable odour and impurities from industrial
gases.
d. Decolouration of yellow glycerene.
Decolouration of yellow glycerene.
The critical moisture content in case of drying indicates the __________
rate period.
a. beginning of falling
b. beginning of constant
c. end of falling
d. none of these
beginning of falling
Pick out the wrong statement
a. A horizontal line on the humidity chart indicates the temperature
changes at constant molal humidity.
b. 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.
c. For unsaturated air-water vapor mixture at atmospheric conditions,
the wet bulb temperature & adiabatic cooling lines are the same.
d. 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.
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)
a. μ
b. 1/μ
c. μ^1/2
d. μ2
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
a. 2.0
b. 1.56
c. 1.0
d. 0.56
2
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 ?
a. Lewis reltionship
b. Galileo number
c. Weber number
d. Dean number
Lewis relationship
Plate efficiency in a distillation column is reduced due to the __________
of liquid.
a. entrainment
b. foaming
c. weeping & dumping
d. all (a), (b) & (c)
all a b c
The most efficient cooling tower out of the following is
a. induced draft
b. forced draft
c. natural draft
d. atmospheric
induced draft
Sodium bicarbonate is produced during soda ash manufacture using a
__________ tower.
a. plate
b. baffle
c. packed
d. none of these
baffle
Powdery materials can be guarded against caking tendency on storage by
a. providing irregular grain size.
b. providing minimum percentage of voids.
c. having maximum possible points of contact.
d. none of these.
none of these
In case of cooling towers, the ratio of the rates of heat and mass transfer is
indicated by the __________ number.
a. Lewis
b. Grashoff
c. Sherwood
d. none of these
Lewis
Which one of the following devices is not used for both the absorption as
well as the liquid-liquid extraction processes ?
a. Packed towers
b. Plate towers
c. Spray towers
d. Wetted wall columns
wetted wall columns
The temperature of water cooled in cooling tower is always __________
temperature of entering air.
a. more than the wet bulb
b. less than the wet bulb
c. equal to the wet bulb
d. equal to the dry bulb
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?
a. Humidification only
b. Heating only
c. Both heating and humidification
d. Evaporative cooling
both heating and humidification
Mass transfer co-efficient is directly proportional to DAB according to the
__________ theory.
film
Tower diameter may be decreased by
a. using higher reflux ratio.
b. use of increased tray spacing.
c. increasing the liquid flow rate.
d. increasing the vapour flow rate.
use of increased tray spacing
Rayleigh’s equation applies to __________ distillation.
a. continuous
b. steam
c. differential
d. flash
differential
Steady state equimolal counter diffusion is encountered in
a. separation of a binary mixture by distillation.
b. absorption of NH3 from air by water.
c. all liquid-liquid diffusion systems.
d. all liquid-solid diffusion systems
separation of a binary mixture by distillation.
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 ?
a. Cost
b. Availability
c. Toxicity
d. Selectivity
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)
a. log P vs . T
b. log P vs. log T
c. T vs. P
d. P vs . log T
log P vs T
The unit of volumetric diffusivity is
a. cm2/sec
b. cm/sec
c. cm3/sec
d. cm2/sec2
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.
a. binary mixture is represented by the apex
b. binary mixture is represented by any point inside
c. ternery mixture is represented by the sides
d. pure component is represented by the apex.
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
a. 100
b. 10
c. 5
d. 1
10
The slope of 9-line is determined by the
a. reflux ratio
b. plate efficiency to be achieved
c. thermal condition of the feed
d. relative volatility.
thermal condition of the feed
In steam distillation, the
a. temperature is 100°C.
b. temperature is more than 100° C.
c. product must be immiscible with water.
d. temperature is higher than the boiling point of either component.
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 ?
a. Dew point
b. Humidity ratio
c. Wet bulb temperature
d. None of these
Wet bulb temperature
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
a. increase
b. decrease
c. remains same
d. depend on saturated boiling point; may increase or decrease
increase
Rose oil is extracted from rose leaves using __________ distillation.
a. high pressure
b. low pressure
c. extractive
d. steam
steam
Hypersorption refers to a __________ process.
a. fixed bed absorption
b. moving bed absorption
c. fixed bed adsorption
d. moving bed adsorption
moving bed adsorption
Extraction of coffee from its seed is done by
leaching
In azeotropic mixture, the equilibrium vapour composition is
a. more than liquid composition.
b. less than liquid composition.
c. same as liquid composition.
d. independent of pressure.
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
a. mass diffusivity to momentum diffusivity.
b. thermal diffusivity to mass diffusivity.
c. momentum diffusivity to thermal diffusivity.
d. none of these.
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)
a. D
b. D2
c. D0.5
d. 1/D
D
Dry bulb temperature of the gas is __________ the wet bulb temperature.
a. less than
b. more than
c. equal to
d. none of these
more than
Decoction refers to the use of solvent
a. at ambient temperature
b. at its boiling point
c. in its vapor form
d. none of these
at its boiling point
Flash distillation is suitable for separating the constituents of a binary
system, which
a. form minimum boiling azeotrope.
b. have very wide boiling points.
c. have very close boiling points.
d. form constant boiling azeotrope.
have very wide boiling points.
The rough value of diffusion co-efficient of water vapor into air at 25°C
may be about __________ cm2/sec.
a. 0.25
b. 2.5
c. 1.25
d. 0.0025
0.25
Flooding in a column results due to
a. high pressure drop
b. low pressure drop
c. low velocity of the liquid
d. high temperature
HIGH PRESSURE DROP
Which of the following gas-liquid contacting devices incurs the least
pressure drop for a particular duty ?
a. Grid tray tower
b. Perforated tray tower
c. Wetted wall tower
d. Bubble cap tower
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?
a. The mixture exhibits an azeotrope at 101.3 kPa.
b. The composition of the mixture, in percent by volume is: o-xylene
30, p-xylene 60. and m-xylene 10.
c. The composition of the mixture in mole percent is: o-xylene 30, p
xylene 60 and m-xyoene 10.
d. The mixture contain optical isomers.
he 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
a. and humidified.
b. and dehumidified with increase in wet bulb temperature.
c. at the same relative humidity.
d. and dehumidified with decrease in wet bulb temperature.
and dehumidified with decrease in wet bulb temperature.
The process employing desorption of the absorbed solute by a solvent is
called
elution
Which of the following operations does not involve leaching ?
a. Dissolving gold from ores.
b. Dissolving pharmaceutical products from bark or roots.
c. Dissolving sugar from the cells of the beet.
d. Removing nicotine from its water solution by kerosene
Removing nicotine from its water solution by kerosene
The recovery of pencillin from the acidified fermentation broth is done by
a. distillation
b. evaporation
c. absorption
d. liquid extraction
liquid extraction
Molecular seives are porous
a. alumina.
b. silica.
c. synthetic zeolites crystals/metal alumino-silicates
synthetic zeolites crystals/metal alumino-silicates
Calcium ammonium nitrate (a fertiliser) is dried in a __________ dryer.
a. rotary
b. vacuum
c. tunnel
d. tray
rotary
A binary mixture of benzene and cyclohexane is separated by
a. flash vaporisation
b. extractive distillation
c. solvent extraction
d. ordinary distillation
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
a. mass transfer is accompanied by reaction.
b. diffusion of A is in stagnant medium B.
c. molecular mean free path is high.
d. there is equimolar counter diffusion.
there is equimolar counterdiffusion
Cox chart is useful in the design of
a. distillation column
b. evaporator
c. dryer
d. crystallizer
distillation column
Dew point of an air-water vapor mixture
a. decreases with decrease in pressure.
b. at constant humidity & total pressure is fixed.
c. corresponding to any point on the humidity chart is obtained by
projecting a line through this point parallel to the temperature axis
and to the saturation curve.
d. All ‘a’, ‘b’ & ‘c’.
all a b c
Can a cooling tower cool water below the wet bulb temperature of inlet air
?
no
The suitable evaporator for concentration of foaming liquids is a
__________ evaporator.
a. long tube
b. short tube
c. vacuum
d. falling film
long tube
The ratio of Murphree plate efficiency to point efficiency is always > 1 in
a __________ flow model.
plug
Tea percolation employs
a. liquid-liquid extraction
b. leaching
c. absorption
d. none of these
leaching
Which of the following assumes constant molal vaporisation and overflow
?
a. McCabe-Thiele method
b. Ponchan-Savarit method
c. Enthalpy concentration method
d. Plate absorption column
a. 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
a. 1
b. >1
c. < 1
d. 0
> 1
Pick out the wrong statement pertaining to leaching.
a. Fine solids can not be leached in a Pachuka tank.
b. Door classifier can be used for leaching of coarse solids.
c. Vegetable seeds can be leached in either of Bollman extractor,
Rotocel or Kennedy extractor.
d. Very high temperature is not needed for the leaching of sugar beet.
Fine solids can not be leached in a Pachuka tank.
Wet bulb and dry bulb temperatures becomes identical at __________
percent saturation curve.
a. 100
b. 50
c. 78
d. none of these
100
McCabe-Thiele method
a. uses molal units for material and energy balance.
b. uses weight fractions to express liquid and vapour composition.
c. can use any type of units.
d. is more accurate than Ponchan-Savarit method.
uses molal units for material and energy balance.
The film penetration model of mass transfer was enunciated by
a. Gilliland
b. Toor and Marchello
c. Stefan
d. Fick
Toor and Marchello
The most economical range of absorption factor is
a. 0 to 0.5
b. 0 to 3
c. 1.25 to 2
d. 5 to 15
1.25 to 2
Channelling is most severe
a. in towers packed with stacked packing.
b. in towers packed randomly with crushed solids.
c. in dumped packing of regular units.
d. at very high liquid flow rate.
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
a. not possible in the second case unless vacuum is applied.
b. not possible in the second case unless high pressure is applied.
c. more readily done in the second case compared to first one.
d. none of these
more readily done in the second case compared to first one.
‘ADDUCTS’ and ‘CLATHRATES’ are used in case of
crystallization
Adsorption is an unit operation which generally involves __________
systems.
a. liquid-solid
b. gas-solid
c. fluid-solid
d. solid-solid
fluid-solid
In case of __________ distillation, a solvent is added to alter the relative
volatility of the mixture to be separated.
a. molecular
b. azeotropic
c. extractive
d. flash.
extractive
Separation of the isotopes of helium for scientific investigations is done by
a. reverse osmosis
b. thermal diffusion
c. leaching
d. solvent extraction
thermal diffusion
In a binary system, separation is very efficient, when the relative volatility
is
> 1
Fenske-Underwood equation used for calculating the minimum number of
theoretical plates in distillation column is valid for
a. constant molal overflow
b. total reflux
c. constant relative volatility
d. all (a), (b) and (c)
all a b c
The binary diffusivity in gases does not depend upon the
a. pressure
b. temperature
c. nature of the components
d. none of these
none of these
Berl saddle made of carbon cannot be used for
a. alkalis
b. SO2
c. H2SO4
d. oxidising atmosphere
oxidizing atmospher
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
a. 0.4
b. 0.25
c. 0.2
d. 0.175
0.2
uring drying of a solid, the critical moisture content increases with
a. decreased drying rate
b. increased thickness of the solid
c. increased drying rate
d. both (b) and (c).
both
Priming in a distillation column
a. results from very low gas velocity.
b. is desirable from point efficiency consideration.
c. is characterised by the presence of foam throughout the space
between trays.
d. reduces the overall pressure drop.
is characterised by the presence of foam throughout the space
between trays.
The commonly used solvent in supercritical extraction is
a. methyl ethyl ketone.
b. water.
c. carbon tetrachloride.
d. carbon dioxide.
carbon dioxide
When the liquid over a plate is of uniform concentration, then
a. Murphree efficiency > point efficiency.
b. Murphree efficiency < point efficiency.
c. Murphree efficiency = point efficiency.
d. Murphree efficiency ≠ point efficiency
Murphree efficiency = point efficiency.
In saturated gas, the
a. vapour is in equilibrium with the liquid at the gas temperature.
b. vapour is in equilibrium with the liquid at the room temperature.
c. partial pressure of vapour equals the vapour pressure of the liquid
at room temperature.
d. none of these.
vapour is in equilibrium with the liquid at the gas temperature.
As per Gilliland’s equation, the diffusivity is
a. directly proportional to ‘T1.5’.
b. inversely proportional to ‘P’.
c. dependent on the molecular volume & molecular weight of
components.
d. all ‘a’, ‘b’ & ‘c’.
all a b c
Pick out the wrong statement.
a. 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.
b. 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.
c. The operating line lies above the equilibrium curve in case of a gas
desorber.
d. 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.
The operating line lies above the equilibrium curve in case of a gas
desorber.
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.
a. 21.7
b. 20
c. 27.3
d. 18.7
18.7
Which of the following is not fixed by the process requirements, in the
design of absorbers ?
a. Flow rate of the entering gas.
b. Composition of the entering liquid.
c. Terminal concentrations of gas stream.
d. None of these.
none of these
If the amount of the steam used in steam distillation is increased, the
temperature of distillation
a. increases
b. decreases
c. remains unchanged
d. depends on relative volatility
decreases
Moisture in a solid exerting an equilibrium vapour pressure equal to that
of the pure liquid at the same temperature is called the __________ moisture.
a. unbound
b. critical
c. free
d. bound
unbound
inside the distillation columns, the
a. highest temperatures is near the feed plate.
b. driving force for the liquid flow is its weight.
c. vapors are not always at their dew points.
d. all (a), (b) and (c)
driving force for the liquid flow is its weight.
When the psychometric ratio is __________ then the adiabatic saturation
temperature and wet bulb temperature becomes equal.
1
Desirable value of absorption factor in an absorber is
> 1
Refractory bricks are usually dried in a __________ dryer.
a. tray
b. tunnel
c. conveyor
d. festoon
tunnel
- What is the degree of freedom of an absorption process in which only one
component is transferred between phases ?
a. 3
b. 2
c. 4
d. 1
3
Sticky material can be dried in a __________ dryer.
a. tray
b. rotary
c. fluidised bed
d. none of these
tray
Langmuir equation is associated with
a. leaching
b. adsorption
c. steam distillation
d. multicomponent absorption.
adsorption
During the constant rate period of drying of a solid,
a. increased air humidity decreases the rate of drying.
b. increasing the air temperature decreases the drying rate.
c. surface evaporation of unbound moisture occurs.
d. none of these.
surface evaporation of unbound moisture occurs.
At a fixed total pressure, humidity depends only on the
a. partial pressure of vapour in the mixture.
b. heat capacity of the vapour.
c. density of the vapour.
d. none of these.
partial pressure of vapor in the mixture
flash distillation is
a. same as differential distillation.
b. used for multicomponent systems like crude refining.
c. same as simple distillation.
d. most useful for handling binary systems.
used for multicomponent systems
__________ developed the film theory.
a. Higbie
b. Fick
c. Ergun
d. Levenspeil
higbie
For absorbers, high pressure drop results in
a. increased efficiency.
b. decreased efficiency.
c. high operating cost.
d. better gas liquid contact.
high operating cost
Which of the following parameters remains almost constant during
adiabatic saturation of unsaturated air ?
a. Dry bulb temperature
b. Dew point
c. Wet bulb temperature
d. None of these
wet bulb temperature
Coffee is prepared from coffee beans by leaching with
hot water
With increase in absolute humidity, the dew point of an unsaturated
mixture of air and water vapor (at constant pressure and temperature)
a. increases
b. remains unchanged
c. decreases
d. decreases linearly
increases
- Pick out the wrong statement. Raoult’s law does not apply, when the
a. size of component molecules are not equal.
b. attractive forces between like and unlike molecules in the solution
are approximately equal.
c. component molecules are nonpolar.
d. chemical combination or molecular association between unlike
molecules takes place in the formation of solution.
component molecules are non polar
Water-ethyl alcohal solution can be concentrated (in respect of alcohal
concentration) by __________ distillation.
a. atmospheric
b. vacuum
c. high pressure
d. none of these
vacuum
L/mGis the expression for
a. absorption factor
b. Brinkman number
c. slope of operating line in absorber
d. slope of operating line in stripper.
absorption factor
In case of gases, the binary diffusivity is proportional to (where, P =
pressure)
a. P
b. 1/P
c. 1/P1/2
d. P1/2
1/P
When the gas to be dissolved in liquid is a/an __________ then normally
co-current adsorber are used.
a. mixture of two gases
b. pure gas
c. ideal gas
d. sparingly soluble gas
PURE GAS
Corresponding to Prandtl number in heat transfer, the dimensionless group
in mass transfer is the __________ number.
a. Schmidt
b. Sherwood
c. Peclet
d. Stanton
Schmidt
If a two phase system is in physical equilibrium; then it means that, the
a. escaping tendency of each component from the liquid phase to the
vapor phase is exactly equal to that from vapor phase to liquid
phase.
b. temperature of the liquid phase is equal to that of the vapor phase.
c. total pressure throughout the liquid phase is equal to that
throughout the vapor phase.
d. all (a), (b) and (c).
all a b c
McCabe-Thiele method of binary distillation does not assume that the
a. sensible heat changes are negligible compared with latent heat
changes.
b. molar latent heats of all components are equal.
c. heat of mixing is negligible.
d. none of these
(NSh/NRe.NSc) is termed in mass transfer operation as the
a. Stanton number
b. Peclet number
c. thermal diffusivity
d. momentum diffusivity
Stanton
The Hatta number is important in
a. multicomponent distillation.
b. binary distillation.
c. gas absorption without chemical reaction.
d. gas absorption with chemical reaction.
gas absorption with chemical reaction.
. When a multistage tray tower uses a minimum reflux ratio, it implies
a. infinite trays and maximum reboiler heat load.
b. infinite trays and minimum reboiler heat load.
c. minimum trays and minimum reboiler heat load.
d. minimum trays and maximum reboiler heat load
inifnite trays minimum reboiler
For the same process conditions, the reflux ratio of an unlagged distillation
column
a. decreases in winter
b. increases in winter
c. increases in summer
d. none of these
increases in winter
. CO2 can be absorbed by
a. hot cupric oxide
b. heated charcoal
c. cold Ca(OH)2
d. alumina
heated charcoal
An ideal tower packing should not
a. have low weight per unit volume.
b. have large surface area per unit volume.
c. have large free cross-section.
d. hold up large amount of liquid in the packing.
hold up large amount of liquid in the packing
Which of the following is a suitable absorbent for removal of H2S from
natural gas ?
a. Vetrocoke solution
b. Monoethanol amine (MEA)
c. Dilute
d. Hot water
Monoethanol amine (MEA)
Acetone is to be removed from air in an isothermal dilute absorber using
pure water as solvent. The incoming air contains 5 mole% of acetone (yin =
0.05). The design equation to be used for obtaining the number of trays (N) of
the absorber is, N+2 = 6 log (yin/yout).For 98% recovery of acetone, the
number of trays required is/are
a. 1
b. 8
c. 9
d. 10
9
Schimdt number and Lewis number for pure air at atmospheric conditions
are respectively
a. < 1 and ≈ 1
b. 1 and 0
c. >1 and ≈ 1
d. 0 and ≈ 1
< 1 and ≈ 1
Molecular diffusion is caused by the
a. transfer of molecules from low concentration to high concentration
region.
b. thermal energy of the molecules.
c. activation energy of the molecules.
d. potential energy of the molecules
thermal energy
At __________ reflux, theoretical number of plates in a distillation
coloumn is calculated using Fenske-Underwood equation.
a. operating
b. total
c. minimum
d. maximum permissible
total
Separation of a mixture of two gases by absorption in the liquid solvent
depends upon the difference in their
a. viscosity
b. density
c. solubility
d. relative volatility
solubility
components, having widely different boiling point in a binary mixture, can
be separated using __________ distillation.
a. molecular
b. extractive
c. steam
d. simple
simple
Which of the following equipments is not used in liquid-liquid extraction ?
a. Pachuka tank
b. Agitated vessels
c. Centrifugal extractors
d. Packed towers
pachuka tank
Pick out the wrong statement.
a. 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.
b. Packed towers are preferred over plate towers for handling
corrosive and foamy liquids.
c. Diameter of randomly packed tower is normally more than 1.2
metres.
d. Due to uneven supply and improper distribution of liquid, problem
of channeling, loading & flooding is generally encountered in
packed towers.
Diameter of randomly packed tower is normally more than 1.2
metres.
Equilibrium-moisture curves of different solids
a. are different
b. are same
c. depend on the humidity of the gas
d. none of these
are different
Azeotropism for ethyl alcohol-water system disappears by
a. increasing temperature
b. decreasing pressure
c. increasing pressure
d. no means
decreasing pressure
Degree of freedom for leaching and solvent extraction process is
a. 1
b. 3
c. 0
d. 2
3
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
a. mass transfer co-efficient.
b. thermal diffusivity.
c. kinematic viscosity.
d. volumetric diffusivity.
mass transfer co-efficient.
