Mass Transfer 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
0.5
Fenske equation determines the
minimum number of theoretical plates.
The term “cooling range” 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 amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by
both (a) and (b).
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.
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.
On addition of solute in the solvent, the __________ of the solution decreases.
both (b) and (c)
Which is the controlling factor for a drum drier?
Heat transfer
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
both ‘a’ & ‘b’
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.
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
specific heat
To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)
increase ‘S’ and 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.
In a packed absorption tower, if the equilibrium and operating lines are both straight lines, then the ratio, HETP/HTUOG __________ the absorption factor.
both (a) and (b)
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
Which of the following remains constant during sensible cooling process?
Both (a) and (b)
Physical absorption is
both (b) and (c)
Make up water is required in a cooling tower to replace the water lost by
all (a), (b) and (c)
Which of the following quantities need not be fixed before starting the design of a co-current absorber?
Flow rate of entering liquid
Mass transfer co-efficient of liquid is
affected more by temperature than that for gases.
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?
Wetted wall column
The equipment frequently used for adiabatic humidification-cooling operation with recirculating liquid is
spray chamber
Chemisorption (chemical adsorption) is
an irreversible phenomenon.
The rate of solid-liquid extraction is limited by the
all ‘a’, ‘b’ & ‘c’.
Raoult’s law applies to the
solvents.
In distillation columns, the number of bubble caps per tray primarily depends upon the
allowable gas and liquid velocities.
In distillation, overhead product contains
any number of components
With increase in pressure, the relative volatility for a binary system
decreases.
Low viscosity absorbent is preferred for reasons of
all (a), (b) and (c).
Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as
K ∝ D
The McCabe Δ L law states that the
linear crystal growth rate does not depend on the crystal size.
Bollman extractor
is used for extraction of oil from oilseed.
The relation, Sc = Pr = 1, is valid, when the mechanism of __________ ansfer is same.
heat and mass
A coalescer in a mixer-settler liquid-liquid extraction coloumn
all ‘a’, ‘b’, & ‘c’.
For the same feed, feed quality and separation (in a distillation column), with the increase of total pressure, the number of ideal plates will
increase
Pick out the correct statement.
Ponchan-Savarit method is more accurate than McCabe-Thiele method to determine the number of theoretical stages required for the separation of non-ideal binary system by distillation.
When the liquid phase and vapour phase of a binary system obeys Raoult’s and Dalton’s law respectively, the relative volatility is the ratio of
vapour pressure of component A to that of component B.
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,
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
all (a), (b) and (c).
__________ diffusion is used for separating the isotopes of methane.
Thermal
Ordinary diffusion process is also called __________ diffusion.
concentration
Pick out the wrong statement.
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.
Rotary dryer is suitable for drying sticky material.
The reason for preferring packed towers over plate towers in distillation practice is that the packed tower operation gives
low pressure drop and 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
0.5
Raoult’s law is applicable to the
ideal solutions
Weeping in a distillation column
results due to very low gas velocity.
In case of binary distillation, increasing the reflux ratio above optimum does not result in the increase of
area between operating line and 45° diagonal x-y diagram.
Wetted wall tower experiment determines the
mass transfer co-efficient.
In 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
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.
ethyl alcohol-water
Free flowing granular materials can be best dried in a __________ drier.
rotary
In case of an ideal solution, the total vapor pressure varies __________ with the composition expressed as mole fraction,
linearly
Corresponding to Nusselt number in heat transfer, the dimensionless group in mass transfer is the __________ number.
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
its recovery cost by distillation may be prohibitatively high.
At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid __________ that in dry packed tower.
is greater than
Molarity is defined as the number of gm moles of solute per __________ of solvent.
liter
The value of Lewis number (Le = Sc/Pr) for air-water vapour system is around
1
An aqueous solution of methanol is to be distilled in a tray column. High pressure steam is available as a source of heat. For a given reflux ratio and overhead composition, two options are being explored; (i) a reboiler is used and (ii) no reboiler is used but steam is fed directly to the bottom of the column. As compared to option (i), in option (ii)
less number of trays are required.
The partial pressure distribution of an ideal gas diffusing through another stagnant ideal gas at steady state follows a/an __________ law.
exponential
Which of the following binary systems is an example of a maximum boiling azeotrope?
Water-hydrochloric acid.
(NRe . NSc) is termed in mass transfer operation as the __________ number.
Peclet
The binary diffusivity in gases and liquids vary respectively as
T^3/2 and T
Pick out the correct statement.
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.
Electrodylsis is used in the manufacture of NaOH.
Pick out the correct statement.
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
avoid channelling
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
ion-exchange
Make up water is supplied during cooling tower operation to compensate for water losses due to
all (a), (b)&(c)
Pick out the wrong statement.
Azeotropes obey Raoult’s law at all temperature.
A minimum boiling azeotrope is exemplified by
acetone-carbon disulphide
Which of the following solutions will follow Raoult’s law most closely?
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)
decreases pressure drop, increases surface area.
Critical humidity of a solid salt means the humidity
both (a) and (b).
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
that of normal condensation.
Absorption with chemical reaction’ is involved in the removal of
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:
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.
Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.
Only small amount of evaporation of water produces large cooling effects because of its
large latent heat
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
both operating and equilibrium lines are parallel.
Flights in a rotary dryer are provided to
lift and shower the solids thus exposing it thoroughly to the drying action of the gas.
If f = moles of vapour present per mole of feed, then the slope of feed line is (Mcabe-Thiele method)
NAME?
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
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
none of these.
At equilibrium the concentration of water in vapour phase (C)in kg/m3 of air space and the amount of water (m) adsorbed per kg of dry silica gel are related by, C = 0.0667m. To maintain dry conditions in a room of air space 100m3 containing 2.2 kg of water vapour initially, 10 kg of dry silica gel is kept in the room. The fraction of initial water remaining in the air space after a long time (during which the temperature is maintained constant) is
0.4
Dry bulb temperature of unsaturated air is more than its __________ temperature.
both ‘a’ & ‘b’
For the case of flow of air past a wet bulb thermometer (air water vapour system), the approximate value of h2/ky.Cz is around
1
The reciprocal of stripping factor is termed as
absorption factor
Ponchan-Savarit method analyses the fractional equipment based on
both enthalpy and material balances.
The binary diffusivity in gases at atmospheric conditions is about
10^-1 cm2/sec
Percentage saturation is __________ the relative saturation.
always smaller than
In case of a desorber (stripper), the
operating line always lies below the equilibrium curve.
What is the reflux ratio at total reflux?
Infinity
Under conditions of flooding in packed tower, the gas pressure drop
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).
Oct-60
For absorbing a sparingly soluble gas in a liquid
liquid side mass transfer co-efficient should be increased.
Channelling in a packed tower results from the
both (b) and (c)
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
all (a), (b) & (c)
In a counter-current liquid extractor
only one of the liquids may be pumped at any desired rate.
Which of the following is an undesirable property for an absorbing solvent ?
None of these
The wetted wall tower is used to determine
individual mass transfer co-efficient (M.T.C.) in gaseous system.
Weight of 1 m3 of humid air as compared to 1 m3 of dry air, under the same conditions, is
less
Positive deviation from Raoult’s law means a mixture whose total pressure is
greater than that computed for ideality.
With increase in gas rate, the number of transfer units, NtoG, for a fixed degree of absorption by a fixed amount of solvent
increases
Schmidt number is given by
μ/ρDAB
The caking of crystals can be prevented by
both (a) and (c)
Prandtl number for water at 20°C is about
7
Boiling point diagram is
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,
all (a), (b) and (c).
Steam distillation is used to
avoid thermal decomposition of a component.
Freundlich equation applies to the adsorption of solute from
dilute solutions, over a small concentration range.
For ethanol-water system, the lowering of distillate quality from 95% to 92% will cause __________ plate requirement.
marginal decrease in the number of
The apex of an equilateral-triangular coordinate (in ternary liquid system) represents a/an
pure component
The diffusivity (D) in a binary gas mixture is related to the pressure (P) as
D ∝ 1/P
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?
Heating and dehumidification at almost constant wet bulb temperature.
In gas-liquid contact operation, the number of ideal stages, https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/331-646-1.png . This is true when the stripping factor ‘S’ is (see picture)
S > 1
The cooling effect in a cooling tower can not be increased by
none of these.
The value of NA/(NA + NB) for steady state molecular diffusion of gas ‘A’ through non-diffusing gas ‘B’ is
1
The humid volume may be increased by increasing the
both (a) and (b).
Pick out the wrong statement
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 bed
Azeotropic distillation is employed to separate
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
∞
Use of natural draft cooling tower is practised, when the air has low
both ‘a’ & ‘b’
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
Dorr thickener is an equipment used for
sedimentation
Steam distillation is used to separate
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
q = 1
Which of the following is an undesirable property in a tower packing?
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
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
molal
The Kundsen diffusivity is proportional to (where, T = absolute temperature)
sqrt(T)
In case of constant underflow extraction operation, the __________ at all solute concentration.
both(a) & (b)
In an absorption coloumn, the flooding velocity for random packing is __________ that for stacked/regular 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.)
Kc = Kp . RT = Km . RT/p
With increase in temperature, the leaching rate increases because of the
both (a) and (b).
Leaching of uranium ore and gold ore is done in
Pachuka tanks
Blowdown in a cooling tower
means discarding a small fraction of circulating water to prevent and limit the concentration of salt and impurities.
During constant rate period, the rate of drying decreases with the
both (a) and (b)
Antibiotics are best handled in a
Podbielniak extractor.
The fixed cost of a distillation column at minimum reflux ratio is
infinite
__________ extractor uses centrifugal force for separating the two phases.
Podbielniak
In a binary distillation column, if the feed contains 40 mole % vapour, the q line will have a slope of
-1.5
Pick out the wrong statement.
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
solvent extraction
Design calculation for multiple component distillation is done by
tray to tray calculations.
To get high tray efficiency
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
dependent on the Reynolds number
Pick out the wrong statement. Generally for physical adsorption, a gas of
none of these.
In most of the mechanically agitated liquid-liquid extractors, baffles or horizontal compartmental plates are provided, which helps in
all ‘a’, ‘b’ & ‘c’.
In a vapor-liquid contacting equipment, the overall gas phase mass transfer co-efficient (M.T.C), KG is related to individual co-efficients (KG and KL) as
1/KG = 1/KG + m/KL
Solvent extraction is the terminology applied to the liquid-liquid extraction, which is preferred for the separation of the components of liquids, when
one of the liquid components has very high affinity towards the solvent.
Inside the distillation column, the
driving force for the vapour flow is the pressure drop.
Diffusivity in concentrated solutions differs from that in dilute solutions, because of the changes in
both (a) and (b).
Occurrence of ‘case hardening’ during drying of a high moisture solid cake __________ the drying rate.
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
temperature
An azeotropic mixture is a __________ mixture.
constant boiling point
Pick out the wrong statement.
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 continuous distillation, the internal reflux ratio (Ri) and the external reflux ratio (Re) are related as
Ri = Re/1+Re
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
added to alter the relative volatility of the mixture.
Radioactive nuclear waste is treated in
pulsed column extractor
Large scale drying of sugar is done in a __________ dryer.
rotary
__________ temperature is the steady state temperature attained by a small amount of liquid evaporating into a large quantity of unsaturated gas-vapor mixture.
Wet bulb
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
incurs smaller pressure drop.
Which of the following is the most commonly used leaching solvent in vegetable oil industry?
Hexane
In an absorber, HETP does not vary with the
none of these
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
a binary mixture.
In distillation column design, the McCabe-Thiele procedure is inadequate and a Ponchan-Savarit procedure is needed, when
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
gas phase resistance controlled.
As the reflux ratio decreases, the
number of plates increases.
Which of the following equipments is not used for gas dispersion?
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
the fraction vaporised but not the product composition.
The equation, https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/315-483-1.png is for (see attached picture)
steady state equimolar counter diffusion
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
increases
The equation, https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/314-467-1.png is for (see attached ppicture)
stready state diffusion for stagnant case.
Which of these columns incurs the lowest pressure drop?
Packed column (with stacked packing)
In the desorption of highly soluble gas from the liquid, the main resistance will be in the __________ phase.
liquid
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
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
can lie above or below the equilibrium curve.
Which of the following same diameter columns gives lowest pressure drop per unit height?
Packed column (stacked)
Diffusion in concentrated solutins differs from that in dilute solutions, because of the change in the __________ with the concentration of the solution.
both ‘a ‘& ‘b’
Stage efficiency in a leaching process depends on the
both (a) and (b)
Operating velocity in a packed tower is usually __________ the flooding velocity.
half
The Knudsen diffusivity is dependent on the
molecular velocity and por radius of the catalyst.
Minimum possible diameter of a packed coloumn is decided mainly by the
flooding
Solvent used in extractive distillation
forms a low boiling azeotrope.
Capacity of a rotary dryer depends on its
both (a) and (b)
The cooling effect in a cooling tower can be speeded up by
all (a), (b) and (c).
When both the fluids flow concurrently in an absorber, the slope of the operating line is
NAME?
The percentage humidity is less than the relative humidity only at __________ percent humidity.
both zero and hundred
Back-trapping in a distillation column
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?
Activated carbon
In a distillation column, with increase in the reflux ratio, the heat removed in the cooler
increases.
Pick out the wrong statement.
Relative volatility of a binary mixture changes appreciably with the minor change in temperature.
Which of the following is not a unit of mass transfer co-efficient?
None of these
The falling rate period in the drying of a solid is characterised by
increasing 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?
None of these
Which of the following equipments is not used for liquid dispersion?
Agitated vessels
Diameter of raschig rings used in packed tower in industry is normally around __________ inches.
2
The diffusion co-efficient in m2 /s. of acetic acid in benzene (liquid in liquid) is
2.09 x 10-9
Pick out the wrong statement.
According to film theory for equimolar counter diffusion, the mass transfer coefficient is given by sqrt(DAB)(b)P - 3, Q - 2
In case of non-ideal gases and liquids, the molal diffusivity
is 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)
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
momentum diffusivity/mass diffusivity.
In case of liquids, the binary diffusivity is proportional to (where, T = temperature)
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.
penetration
Sand is dried in foundaries in a___drier.
fluidised bed
Which of the following employs an accessory known as ‘drift eliminator’?
Mechanical draft cooling tower.
Pick out the correct statement.
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.
all (a), (b) and (c).
Humid volume is the total volume in m3 of 1 kg of
gas plus its accompanying vapour at 1 atm. and gas temperature.
Diameter to height ratio for a rashig ring is
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
all ‘a’, ‘b’ & ‘c’
With increase in temperature, the rate of extraction in leaching (solid-liquid extraction system)
increases
In a packed bed absorption column, the channelling will be noted by the
sharp drop in pressure drop.
Gaseous diffusivity at atmospheric pressure is of the order of __________ cm2/second.
1
In liquid-liquid extraction, the number of phases at plait point is
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.
The entire amount of C is transferred to solvent B.
The surface renewal frequency in Danckwerts’ model of mass transfer is given by (KL: mass transfer co-efficient)
sqrt(KL2.DA)
If Rm is the minimum reflux ratio, the optimum reflux ratio may be around __________ Rm.
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.
wet bulb temperature
In case of absorption, both the operating and equilibrium lines will be straight for
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
dilute solution and isothermal operation.
A distillation column separates 10000 kg/hr of a benzene-toluene mixture as shown in the figure below: https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/335-680-1.png 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
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
momentum diffusivity to the mass diffusivity.
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
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.
interface
Pick out the wrong statement pertaining to the analogy between equations of heat and mass transfer operations.
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
(-) 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?
gas side
Pore size of the molecular seive 5A is __________ mm.
0.5
Swenson-Walker crystalliser is a __________ unit
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.
12
Absorption (liquid-gas system) with evolution of heat as compared to isothermal absorption results in
all (a), (b) and (c).
With increase in temperature, the mutual solubility of two liquids
increases
Pick out the wrong statement.
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
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.
less than
Lewis number (Le) is
Sc / Pr
Which of the following is not a continuous leaching equipment?
Pachuka tank
__________ 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.)
(1 + Ro) = Ro/Ri
Separation of __________ employs gaseous diffusion process.
isotopes of uranium
For water-ethanol system, the minimum 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)
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.
mass transfer co-efficient
Pick out the wrong statement:
In case of a stripper, the equilibrium curve is always below the operating line.
In liquid extraction, if the selectivity is unity, then
no separation will occur.
Paper industry employs __________ driers.
cylinder
Which of the following has the same dimension as mass diffusivity?
Both (b) and (c)
Pick out the wrong statement pertaining to the cooling towers.
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
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
avoid channeling.
Co-current absorbers are usually used when the gas to be dissolved in the liquid is
a 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.
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
Co-efficient = Flux/concentration difference.
When an unsaturated air-water mixture is heated at constant pressure, then
the relative humidity decreases.
During sensible cooling process
both (b) and (c)
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
equal to the heat of wetting.
Pick out the wrong statement:
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
1.25 to 2.0
Large scale usage of flash distillation is practised in
petroleum refinning
High pressure at the bottom of a distillation tower handling heat sensitive materials results in
thermal decomposition of bottoms.
Alcohol is dehydrated using __________ distillation.
azeotropic
Separation of two volatile liquids by distillation makes use of their
relative volatility
Which of the following increases during evaporative cooling process with recirculated water supply?
Both (b) and (c)
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.
sticky
Pick out the correct statement.
none of these.
An example of elution is
separation 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
partial pressure
Relative volatility does not change appreciably with the change in
temperature
Boiling point diagram is not affected by the ambient
both (b) and (c)
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?
Temperature of the solid
In case of liquid-liquid binary diffusion, diffusivity of one constituent into another is not dependent on the
none of these
For continuous drying of grannular or crystalline material, the dryer used is the __________ dryer.
rotary
When adsorption hysteresis is observed, the desorption equilibrium pressure is __________ that obtained by adsorption.
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
high reflux ratio
The efficiency of a plate column will be maximum, when the flow is ideal __________ the plate.
both (a) & (b)
Heat load in a cooling tower
both (a) & (b).
In case of absorption with exothermic reaction, for fluids having
both (a) and (b)
Detergent solution is dried to a powder in a
spray dryer
Which of the following mixtures does not form an azeotrope at atmosheric pressure?
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
liquid film
The overall mass transfer co-efficient for the absorption of SO2 in air with dilute NaOH solution can be increased substantially by
increasing the gas film co-efficient.
Flooding results in
low tray efficiency
For the air water system under ambient conditions, the adiabatic saturation temperature and the wet bulb temperature are nearly equal, because
water has a high latent heat of evaporation.
In an operating distillation column, the
driving force for the vapor flow is the pressure drop, as the pressure decreases gradually from the bottom to the top of the column.
In a forced draft cooling tower, water is cooled from 95 to 80°F by exposure to air with a wet bulb temperature of 70°F. In this case, the
both (a) & (b).
The diffusivity (D) in a binary gas mixture is related to the temperature (T) as
D ∝ T^1.5
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.
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.
none of these
The dimension of diffusivity is same as that of the
kinematic viscosity
The temperature to which a vapour gas mixture must be cooled (at varying humidity) to become saturated is called the __________ temperature.
none of these
Entrainer used in azeotropic distillation should
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
mixing of steam with the material being vaporised is not so intimate as to result in equilibrium condition.
Pick out the wrong statement.
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
For contacting a highly soluble gas with a liquid
bubble the gas through liquid.
During drying operation, it is easier to remove the __________ moisture.
unbound
With increase in solvent rate, the number of transfer units, NtoG, for a fixed degree of absorption from a fixed amount of gas
decreases
Ion exchange process is similar to
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,
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
changes the relative volatility of the original components.
Air at a particular humidity is heated in a furnace. The new dew point
increases
In a packed tower, the value of HETP equals HTUOG, when the equilibrium and the operating lines are (where, HETP = height equivalant to a theoretical plate HTUOG = overall gas phase height of a transfer unit)
both (a) & (b)
The vapour pressure exerted by the moisture contained in a wet solid depends upon the
all (a), (b) and (c).
The absorption factor is defined as (where, L = liquid flow rate, G = gas flow rate and, m = slope of the equilibrium line)
L/mG
Smoke is an example of
solid dispersed in gas
Which of the following adsorbant is used in the refinning of sugar?
Bone charcoal
Stacked packing compared to dumped packing
both (a) and (b).
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 dehumidification?
Dry bulb temperature
Drying of a solid involves __________ transfer.
both heat and mass
Mechanism of moisture removal in case of freeze drying of food stuff is by
sublimation
The dew point of an unsaturated gas-vapor mixture does not depend upon the __________ of the mixture.
temperature
Which is not concerned directly with mass transfer?
Froude number
Removal of __________ exemplifies an adsorption unit operation.
water from petrol
Can the efficiency of a plate in the distillation tower be greater than 100%?
Never
With increase in the mass velocity of the gas, the rate of drying during the constant rate period __________ , if the conduction and radiation through the solid are negligible.
increases
For gas absorption, low viscosity solvents are preferred, because of their
all (a), (b) and (c).
To remove all the moisture from a wet solid it requires exposure to __________ air.
perfectly dry
The operating cost of a distillation column at minimum reflux ratio is
minimum
The reflux to a distillation column is 100 moles/hr, when the overhead product rate is 50 moles/hr. The reflux ratio is
2
Molecular diffusivity of a liquid
increases with temperature.
The wet and ‘dry bulb temperature for a vapour-gas mixture are 25°C and 30°C respectively. If the mixture is heated to 45°C at constant pressure, the wet bulb temperature will be __________ °C.
> 25
Henry’s law states that the
partial pressure of a component over a solution is proportional to its mole fraction in the liquid.
Ammonia present in the coke oven gas is removed by washing with
dilute ammoniacal liquor
With increase in temperature, the leaching rate increases due to
both (a) and (b)
Which of the following processes is not an example of adsorption applied to gaseous separations?
Decolouration of yellow glycerene.
The critical moisture content in case of drying indicates the __________ rate period.
beginning of falling
Pick out the wrong statement
Relative saturation of unsaturated mixture of water vapor & air can not be increased by either reducing the mixture temperature or by increasing the total pressure.
According to Poiseuille’s law, the permeability for gas flow through a capillary is proportional to (where, μ = gas viscosity)
1/μ
For a binary mixture distillation process, the degree of freedom is 2. However, if the pressure is fixed in this process, the number of independent variables in this process will be
1
H2S is being absorbed in a gas absorber unit. The height of the transfer unit based on the overall mass transfer coefficient on the gas side is 0.4 m. The equilibrium data is given by, y = 1.5 x. The bulk concentration of H2S has to be reduced from 0.05 to 0.001 mole fraction in the gas side. The height of the tower (in metres) corresponding to an operating line given by, y = 5x + 0.001 is
2
Packed column distillation is limited to the column __________ metres.
both (a) & (b)
For the flow of gases through a capillary, with increase in temperature, the permeability __________ as per Knudsen law.
increases
Which of the following is directly concerned with psychrometry?
Lewis relationship
Plate efficiency in a distillation column is reduced due to the __________ of liquid.
all (a), (b) & (c)
The most efficient cooling tower out of the following is
induced draft
Sodium bicarbonate is produced during soda ash manufacture using a __________ tower.
baffle
Powdery materials can be guarded against caking tendency on storage by
none of these.
In case of cooling towers, the ratio of the rates of heat and mass transfer is indicated by the __________ number.
Lewis
Which one of the following devices is not used for both the absorption as well as the liquid-liquid extraction processes?
Wetted wall columns
The temperature of water cooled in cooling tower is always __________ temperature of entering air.
more than the wet bulb
Which of the following processes is followed by unsaturated air (with dry bulb temperature 12°C and relative humidity 47%) passing through water spray washer (temperature of water being constant at 40°C?
Both heating and humidification
Mass transfer co-efficient is directly proportional to DAB according to the __________ theory.
film
The relative volatility of a binary mixture at constant temperature __________ the total pressure.
decreases with increase in
Tower diameter may be decreased by
use of increased tray spacing.
Rayleigh’s equation applies to __________ distillation.
differential
Steady state equimolal counter diffusion is encountered in
separation of a binary mixture by distillation.
Which of the following is considered equivalent to one theoretical stage in Mc-Cabe Thiele’s method?
Both (b) and (c)
Polar organic compounds are normally used as separating agents for the azeotropic and extractive distillation. Which of the following is the most important factor to be considered for the choice of the separating agent for extractive distillation?
Selectivity
As the reflux ratio increases, the slope of the operating line for rectifying section
increases
Cox chart, which is useful in the design of distillation column particularly for petroleum hydrocarbons, is a plot of (where, P = vapor pressure, T = temperature)
log P vs . T
The unit of volumetric diffusivity is
cm2/sec
For a ternery mixture, in which equilateral triangular co-ordinate is used in leaching and extraction, a __________ of the equilateral triangular co-ordinates.
pure component is represented by the apex.
Steady state temperature reached by a small amount of liquid evaporating into a large amount of unsaturated vapour-gas mixture is called the __________ temperature.
wet-bulb
The Reynolds number of the liquid was increased 100 fold for a laminar falling film used for gas-liquid contacting. Assuming penetrating theory is applicable, the fold increase in the mass transfer co-efficient (Kc) for the same sytem is
10
The slope of 9-line is determined by the
thermal condition of the feed
In steam distillation, the
product must be immiscible with water.
Which of the following can be calculated theoretically using steam table and Dalton’s law of partial pressure; if the relative humidity and dry bulb temperature of moist air is known?
Wet bulb temperature
Steam distillation is used for separation of high boiling
both (a) and (b).
The feed to fractionating column is changed from saturated vapour to saturated liquid. If the separation and reflux ratio remains unchanged, the number of ideal stages will
increase
Rose oil is extracted from rose leaves using __________ distillation.
steam
