Mass Transfer Flashcards
Mass transfer rate between two fluid phases does not necessarily depend
on the __________ of the two phases.
a. chemical properties
b. physical properties
c. degree of turbulence
d. interfacial area
chemical properties
Fenske equation determines the
a. maximum number of ideal plates.
b. height of the distillation column.
c. minimum number of theoretical plates.
d. optimum reflux ratio.
minimum number of theoretical plates.
The term “co” in a cooling tower refers to the difference in the temperature of
a. cold water leaving the tower and the wet bulb temperature of the surrounding air.
b. hot water entering the tower and the wet bulb temperature of the surrounding air.
c. hot water entering the tower and the cooled water leaving the tower.
d. none of these
hot water entering the tower and the cooled water leaving the tower.
Which of the following is the most suitable for extraction in a system having very low density difference?
a. Mixer-settler extractor
b. Centrifugal extractor
c. Pulsed extractor
d. Packed extraction tower
Centrifugal extractor
Total reflux in a distillation operation requires minimum
a. reboiler load
b. number of plates
c. condenser load
d. all (a), (b) and (c)
number of plates
The difference of wet bulb temperature and adiabatic saturation temperature of unsaturated mixture of any system is
a. +ve
b. -ve
c. zero
d. none of these
+ve
Fenske’s equation for determining the minimum number of theoretical stages in distillation column holds good, when the
a. relative volatility is reasonably constant.
b. mixture (to be separated) shows negative deviation from ideality.
c. mixture (to be separated) shows positive deviation from ideality.
d. multicomponent distillation is involved.
relative volatility is reasonably constant.
When the temperature and humidity of air is low, we usually use __________ draft cooling tower.
a. natural
b. forced
c. induced
d. none of these
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).
all
_________ columns are used for liquid dispersion in a continuous gas phase.
a. Packed
b. Pulse
c. Bubble cap
d. Sieve plate
Packed
Overall efficiency of the distillation column is
a. the ratio of number of ideal plates to actual plates.
b. the ratio of number of actual plates to ideal plates.
c. same as the Murphree efficiency.
d. always more than the point efficiency.
the ratio of number of ideal plates to actual plates
Drying operation under vacuum is carried out to
a. dry those materials which have very high unbound mositure content.
b. reduce drying temperature.
c. increase drying temperature.
d. dry materials having high bound moisture content.
reduce drying temperature.
Air initially at 101. 3 kPa and 40°C and with a relative humidity of 50%, is cooled at constant pressure to 30°C. The cooled air has a
a. higher dew point.
b. higher absolute (specific) humidity.
c. higher relative humidity
d. higher wet bulb temperature.
higher relative humidity
Separation of two or more components of a liquid solution can not be achieved by
a. fractional crystallisation
b. liquid extraction
c. absorption
d. evaporation
absorption
At minimum reflux ratio for a given separation
a. number of plates is zero.
b. number of plates is infinity.
c. minimum number of the theoretical plates is required.
d. separation is most efficient.
number of plates is infinity.
Relative humidity is the ratio of the
a. partial pressure of the vapour to the vapour pressure of the liquid at room temperature.
b. partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.
c. actual humidity to saturation humidity.
d. none of these
partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.
In batch distillation with constant reflux, overhead product composition __________ with time.
a. increases
b. decreases
c. does not vary
d. may increase on decrease, depends on the system.
decreases
Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the __________ of a fibre.
a. electrical resistance
b. thermal conductivity
c. strength
d. none of these.
electrical resistance
Heat in BTU necessary to increase the temperature of 1 lb of gas and its accompanying vapour by 1°F is called the
a. latent heat
b. humid heat
c. specific heat
d. sensible heat
specific heat
To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)
a. increase both ‘G’ and ‘S’.
b. decrease both ‘G’ and ‘S’.
c. increase ‘S’ and decrease ‘G’.
d. increase ‘G’ and decrease ‘S’
increase ‘S’ and decrease ‘G’.
The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are same for, NPr = NSc = __________
a. 1
b. 0.5
c. 10
d. 0
1
Dew point of a gas-vapour mixture
a. increases with temperature rise.
b. decreases with temperature rise.
c. decreases with decrease in pressure.
d. increases with increase in pressure.
decreases with decrease in pressure.
Which of the following plays an important role in problems of simultaneous heat and mass transfer ?
a. Lewis number
b. Schmidt number
c. Prandtl number
d. Sherwood number
Lewis number
In case of an absorber, the operating
a. line always lies above the equilibrium curve.
b. line always lies below the equilibrium curve.
c. line can be either above or below the equilibrium curve.
d. velocity is more than the loading velocity.
line always lies above the equilibrium curve.
As the reflux ratio in a distillation coloumn is increased from the minimum, the
a. slope of the operating line in stripping section decreases.
b. number of plates decreases very slowly first and then more and more rapidly.
c. total cost first decreases and then increases.
d. liquid flow increases while the vapor flow decreases for a system.
total cost first decreases and then increases.
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 ternary system containing two pairs of partially miscible liquids?
a. 0
b. 1
c. 2
d. 3
0
Make up water is required in a cooling tower to replace the water lost by
a. evaporation
b. drift
c. blowdown and leakage
d. all (a), (b) and (c)
all
Which of the following quantities need not be fixed before starting the design of a co-current absorber?
a. Heat gain or loss
b. Flow rate of entering liquid
c. Flow rate of gas
d. None of these
Flow rate of gas
Mass transfer co-efficient of liquid is
a. affected more by temperature than that for gases.
b. affected much less by temperature than that for gases.
c. not affected by the temperature.
d. none of these.
affected more by temperature than that for gases.
Absorption accompanied with chemical reaction is exemplified by the absorption of
a. ammonia in water.
b. benzol present in coke oven gas by wash oil.
c. SO2 in alkaline solution.
d. all (a), (b) and (c).
SO2 in alkaline solution.
Which of the following unit operations makes use of Thiele-Geddes equation ?
a. Liquid-liquid extraction
b. Solid-liquid extraction
c. Multicomponent absorption with chemical reaction
d. Multicomponent distillation.
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 column
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
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
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) and (c).
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.
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.
is used for extraction of oil from oilseed.
The relation, Sc = Pr = 1, is valid, when the mechanism of __________ transfer 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
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
a. decoction
b. percolation
c. elutriation or elution
d. none of these
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%).
a. 15 min
b. 51 min
c. 71 min
d. 94 min
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
_________ diffusion is used for separating the isotopes of methane.
a. Thermal
b. Pressure
c. Concentration
d. Force
Thermal
Ordinary diffusion process is also called __________ diffusion.
a. pressure
b. thermal
c. concentration
d. forced.
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.
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.
a. 100
b. >100
c. < 100
d. none of these
> 100
Compound A is extracted from a solution of A + B into a pure solvent S. A Co-current unit is used for the liquid-liquid extraction. The inlet rate of the
solution containing A is 200 moles of B/hr.m2 and the solvent flow, rate is 400 moles of S/m2. hr. The equilibrium data is represented by Y = 3X2 , where Y
is in moles of a A/moles of B and X is in moles A moles of S. The maximum percentage extraction achieved in the unit is
a. 25%
b. 50%
c. 70%
d. 90%
50%
Raoult’s law is applicable to the
a. ideal solutions
b. real solutions
c. mixture of water and alcohol
d. non-ideal gases
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.
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
a. molal diffusivity.
b. volumetric co-efficient.
c. mass transfer co-efficient.
d. none of these.
mass transfer co-efficient.
With decrease in the throughput (compared with the design capacity) for a bubble cap distillation column, its efficiency
a. increases
b. decreases
c. remains same
d. may increase or decrease; depends on individual design.
increases
Plate towers are preferred to packed towers, when large temperature changes are involved, because of the reason that the
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
a. more
b. less
c. same
d. either more or less; depends on the system
same
Out of the following gas-liquid contacting devices, for a given set of operating conditions, gas pressure drop is the least in __________ tower.
a. wetted wall
b. bubble cap
c. perforated tray
d. packed
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
c. exponentially
d. none of these
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
a. 0.31
b. 0.107
c. 0.017
d. 0.215
0.215
Liquid diffusivity is of the order of __________ cm2 /second.
a. 0.01
b. 0.1
c. 10^-5 to 10^-6
d. > 1
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.
a. is greater than
b. is lower than
c. is same as
d. cannot be predicted as data are insufficient.
is greater than
The value of Lewis number (Le = Sc/Pr) for air-water vapour system is around
a. 1
b. 0.24
c. 3.97
d. 600
1
An aqueous solution of methanol is to be distilled in a tray column. High pressure steam is available as a source of heat. For a given reflux ratio and overhead composition, two options are being explored; (i) a reboiler is used and (ii) no reboiler is used but steam is fed directly to the bottom of the column. As compared to option (i), in option (ii)
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
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.
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 transfer in a wet solid is its free moisture content.
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 channelling
Moisture contained by a substance in excess of the equilibrium moisture is called the __________ moisture.
a. unbound
b. free
c. critical
d. bound
free
In most of the vacuum crystalliser, vacuum is generally produced by means of a
a. suction pump
b. compressed air jet
c. steam jet ejector with a barometric condenser
d. none of these
steam jet ejector with a barometric condenser
On moving the feed line (q-line) from saturated liquid feed (vertical position) to saturated vapor feed (horizontal feed), if the slope of both the operating lines are to be increased, then it will result in
a. greater degree of separation with a fixed number of trays
b. increased reboiler load
c. increased reflux ratio
d. None of these
increased reflux ratio
_________ column is the most suitable for achieving the best performance for mass transfer operations involving liquid with dispersed solids.
a. Watted wall
b. Packed
c. Plate
d. Spray
Plate
Deairation (removal of O2) of water is done by
a. rectification
b. absorption
c. ion-exchange
d. adsorption
ion-exchange
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.
d. The relative volatility of a binary mixture at the azeotropic composition is 1.
Azeotropes obey Raoult’s law at all temperature.
A minimum boiling azeotrope is exemplified by
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
a. parallel
b. straight
c. both parallel and straight
d. neither parallel nor straight
both parallel and straight
As complete saturation of an adsorbent is approached, the differential heat of adsorption 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
a. 0
b. 1
c. >1
d. < 1
> 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.
a. tunnel
b. heated cylinder
c. conveyor
d. festoon
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.
a. raschig
b. lessing
c. cross-partition
d. single spiral
raschig
When the feed to a distillation column is a saturated liquid, slope of the feed line is
a. zero
b. unity
c. infinity
d. none of these
infinity
Leaching of sugar from sugar beets is done by
a. hot water
b. hexane
c. dilute H2SO4
d. lime water
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 consulate 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.
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
is maximum
For achieving rapid drying rate in a spray dryer, the diameter of the particles in the feed should be in the range of __________ microns (1 mm = 1000 microns).
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.
d. mass transfer co-efficient must be kept constant.
liquid side mass transfer co-efficient should be increased.
The change in enthalpy per unit weight of adsorbed gas when adsorbed on gas free or “outgassed” adsorbent to from a definite concentration of adsorbate is called its
a. integral heat of adsorption.
b. heat of wetting.
c. differential heat of adsorption.
d. heat of normal condensation.
integral heat of adsorption.
The minimum number of theoretical plates is required for achieving a given separation in distillation column with
a. no reflux
b. total reflux
c. zero reflux ratio
d. minimum reflux ratio
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
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
a. 7
b. 70
c. 0.7
d. 150
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.
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?
a. Spray dryer
b. Drum dryer
c. Rotary dryer
d. Dielectric dryer
Spray dryer
Which of the following psychrometric processes is followed by water vapour laden unsaturated air, when it is passed through solid or liquid adsorbent?
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
a. S > 1
b. S < 1
c. S = 1
d. S = ∞
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
a. 1
b. ∞
c. 0.5
d. 2
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.
In actual practice, absorption is an en-dothermic process, while stripping is an exothermic process.
Large scale drying of wheat is done in a __________ dryer.
a. fluidised bed
b. spouted bed
c. tray
d. vacuum rotary
spouted bed
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.
At the boiling point of the liquid at the prevailing pressure, the saturated absolute humidity becomes
a. 1
b. 0
c. ∞
d. none of these
∞
Pressure drop through plate tower as compared to that through packed tower, for the same duty will be
a. less
b. more
c. equal
d. either (a) or (b); depends on the packing height
more
Dimension of mass diffusivity is the same as that of
a. kinematic viscosity
b. dynamic viscosity
c. surface tension
d. pressure
kinematic viscosity
Dorr thickener is an equipment used for
a. classification
b. sedimentation
c. clarification
d. leaching
sedimentation
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.
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
a. q > 1
b. q < 1
c. q = 1
d. q = 0
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
a. drift
b. blow down
c. vapor load
d. none of these.
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
a. 1000
b. 1500
c. 2000
d. 2500
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.
a. molal
b. relative
c. percentage
d. none of these
molal
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
Leaching of uranium ore and gold ore is done in
a. centrifugal extractor
b. Pachuka tanks
c. Bollman extractor
d. none of these
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
a. minimum
b. infinite
c. optimum
d. none of these
infinite
_________ extractor uses centrifugal force for separating the two phases.
a. Treybal
b. Schiebel
c. Podbielniak
d. None of these
Podbielniak
Pick out the wrong statement.
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, if the system has low interfacial tension.
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.
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
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
one of the liquid components has very high affinity towards the solvent
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
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?
a. Drum drier
b. Spray drier
c. Tunnel drier
d. Tray drier
Tray drier
Humidification involves mass transfer between a pure liquid phase and a,fixed gas, which is
a. insoluble in the liquid
b. soluble in the liquid
c. non-ideal in nature
d. at a fixed temperature
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.
a. Dew point
b. Bubble point
c. Dry bulb temperature
d. Wet bulb temperature
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.
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.
a. < 150
b. 200-330
c. >500
d. >1000
200-330
In a counter-current extractor, as the axial mixing increases, the extraction efficiency
a. increases
b. decreases
c. remains unchanged
d. depends on the pressure of the system
decreases
Heat sensitive materials like certain pharmaceuticals and food stuffs can be dried in a/an __________ dryer.
a. indirect tray
b. spray
c. freeze
d. none of these
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 extractor
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.
a. Dry bulb
b. Wet bulb
c. Dew point
d. none of these
Wet bulb
_________ equation applies to diffusivities in liquids.
a. Gilliland
b. Hirschfelder
c. Wilke and Chang
d. none of these
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 of these
Large quantity of silica gel is normally dried in a __________ dryer.
a. freeze
b. through circulation
c. rotary vacuum
d. tray
through circulation
For the same system, if the same liquid used in an absorber is decreased, the tower height will
a. increase
b. decrease
c. remain unaffected
d. decrease or increase ; depends on the type of liquid
increase
Hydrogenation of oil is carried out in a/an __________ in Vanaspati manufacturing plant.
a. agitated vessel
b. sieve tray column
c. bubble cap column
d. packed tower
agitated vessel
Sides of equilateral-triangular co-ordinates (on which ternary liquid system is plotted) represent
a. a pure component.
b. a binary mixture.
c. a ternary mixture.
d. partially miscible ternary system.
a 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.
a 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?
a. Relative humidity
b. Partial pressure of vapour
c. Wet bulb temperature
d. None of these
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.
a. half
b. twice
c. equal to
d. more than
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 by the
a. flooding
b. gas viscosity
c. liquid density
d. liquid hold up
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
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
