Mass Transfer Part 2 Flashcards
Solvent extraction is the terminology applied to the liquid-liquid extraction, which is preferred for the separation of the components of liquids, when
extracting solvent is cheaply & abundantly available.
one of the liquid components is heat sensitive.
viscosity of liquid components is very high.
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
driving force for the vapour flow is the pressure drop.
liquids are not always at their bubble points.
pressure increases gradually from bottom to the top of the column.
none of these
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
viscosity with concentration.
degree of ideality of the solution.
both (a) and (b).
neither (a) nor (b).
both (a) and (b).
Occurrence of ‘case hardening’ during drying of a high moisture solid cake __________ the drying rate.
increases
decreases
does not affect
exponentially increases
decreases
Which of the following is not a continuous drier?
Drum drier
Spray drier
Tunnel drier
Tray drier
Tray drier
Humidification involves mass transfer between a pure liquid phase and a fixed gas, which is
insoluble in the liquid
soluble in the liquid
non-ideal in nature
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.
Dew point
Bubble point
Dry bulb temperature
Wet bulb temperature
Dew point
Rate of leaching increases with increasing
temperature
viscosity of solvent
pressure
size of the solid
temperature
An azeotropic mixture is a __________ mixture.
binary
ternary
constant boiling point
none of these
constant boiling point
Pick out the wrong statement.
In the McCabe-Thiele diagram for binary distillation, vertical feed line represents saturated liquid feed and horizontal feed line represents saturated vapour feed.
In small columns, local efficiency is larger than Murphree efficiency; in large columns local efficiency is smaller than Murphree efficiency.
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.
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.
wrong for laminar flow over a plate of length L
Molecular seives are regenerated by heating to __________ C.
< 150
200-330
> 500
> 1000
200-330
In continuous distillation, the internal reflux ratio (Ri) and the external reflux ratio (Re) are related as
Ri = Re/1-Re
Ri = 1-Re/Re
Ri = Re
Ri = Re/1+Re
Ri = Re/1+Re
In a counter-current extractor, as the axial mixing increases, the extraction efficiency
increases
decreases
remains unchanged
depends on the pressure of the system
decreases
Heat sensitive materials like certain pharmaceuticals and food stuffs can be dried in a/an __________ dryer.
indirect tray
spray
freeze
none of these
freeze
In extractive distillation, solvent is
added to alter the relative volatility of the mixture.
of high volatility.
present in overhead stream.
of high viscosity to give high tray efficiency.
added to alter the relative volatility of the mixture.
Radioactive nuclear waste is treated in
mixer-settler extractor
rotating-disc contactor
pulsed column extractor
Bollman extractor
pulsed column extractor
Large scale drying of sugar is done in a __________ dryer.
spouted bed
tray
rotary
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.
Dry bulb
Wet bulb
Dew point
none of these
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)
sqrt(T)
T
T^1.5
T^3
T
__________ equation applies to diffusivities in liquids.
Gilliland
Hirschfelder
Wilke and Chang
none of these
Gilliland
A packed tower compared to a plate tower for a particular mass transfer operation
incurs smaller pressure drop.
allows installation of cooling coils.
is less costly when built in large sizes/diameters.
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?
Phenol
Hexane
Furfurol
Liquid SO2
Hexane
hexane solvent vegetable oil leaching
In an absorber, HETP does not vary with the
flow rate of liquid
flow rate of gas
type and size of packing
none of these
none of these
HETP does not vary none of these
Large quantity of silica gel is normally dried in a __________ dryer.
freeze
through circulation
rotary vacuum
tray
through circulation
For the same system, if the same liquid used in an absorber is decreased, the tower height will
increase
decrease
remain unaffected
decrease or increase ; depends on the type of liquid
increase
Hydrogenation of oil is carried out in a/an __________ in Vanaspati manufacturing plant.
agitated vessel
sieve tray column
bubble cap column
packed tower
agitated vessel
Sides of equilateral-triangular co-ordinates (on which ternary liquid system is plotted) represent
a pure component.
a binary mixture.
a ternary mixture.
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
saturated feed is not used.
an azeotrope forms.
the latent heat of vaporisation of the more and less volatile components are greatly different.
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
liquid phase resistance-controlled.
gas phase resistance controlled.
impossible.
driven by a non-linear driving force.
gas phase resistance controlled.
As the reflux ratio decreases, the
separation becomes more efficient.
number of plates increases.
column diameter increases.
none of these.
number of plates increases.
Which of the following equipments is not used for gas dispersion?
agitated vessel
Bubble cap tray towers
Perforated sieve tray towers
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
the product composition but not the fraction vaporised.
the product composition as well as the fraction vaporised.
the fraction vaporised but not the product composition.
neither the product composition nor the fraction vaporised.
the fraction vaporised but not the product composition.
The equation, NA = DAB . Pt / RTZ is for
steady state equimolar counter diffusion
Fick’s first law of diffusion
steady state diffusion for stagnant case
liquid M.T.C. by penetration theory.
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
decreases
remains unchanged
increases
decreases exponentially
increases
The equation, NA = DAB . Pt / RTZ . PBM is for
Fick’s second law of diffusion.
stready state diffusion for stagnant case.
liquid M.T.C. by Higbie penetration theory.
none of these.
stready state diffusion for stagnant case.
Which of these columns incurs the lowest pressure drop?
Packed column (with stacked packing)
Packed column (with dumped packing)
Bubble plate column
Pulse column
Packed column (with stacked packing)
lowest pdrop packed stacked
In the desorption of highly soluble gas from the liquid, the main resistance will be in the __________ phase.
gas
liquid
both (a) & (b)
neither (a) nor (b)
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
G/L
always < 1
none of these
L/G
Which of the following remains constant during evaporative cooling process with recirculated water supply?
Relative humidity
Partial pressure of vapour
Wet bulb temperature
None of these
Wet bulb temperature
For stripping of a gas in a counter current stripper, the operating line
lies above the equilibrium curve.
lies below the equilibrium curve.
can lie above or below the equilibrium curve.
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?
Bubble-cap column
Sieve-plate column
Packed column (stacked)
Randomly packed column
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.
degree of ideality
viscosity
both ‘a ‘& ‘b’
neither ‘a’ nor ‘b’
both ‘a ‘& ‘b’
Stage efficiency in a leaching process depends on the
time of contact between the solid and the solution
rate of diffusion of the solute through the solid and into the liquid
both (a) and (b)
vapour pressure of the solution
both (a) and (b)
Operating velocity in a packed tower is usually __________ the flooding velocity.
half
twice
equal to
more than
half
The Knudsen diffusivity is dependent on the
molecular velocity only.
pore radius of the catalyst only.
molecular mean free path only.
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
flooding
gas viscosity
liquid density
liquid hold up
flooding
Solvent used in extractive distillation
is of low volatility.
forms a low boiling azeotrope.
forms a high boiling azeotrope.
does not alter the relative volatility of the original components.
forms a low boiling azeotrope.
Capacity of a rotary dryer depends on its
r.p.m
inclination with ground surface
both (a) and (b)
neither (a) nor (b)
both (a) and (b)
The cooling effect in a cooling tower can be speeded up by
increasing the air velocity and area of exposed wet surface.
reducing the barometric pressure.
reducing the humidity of the air.
all (a), (b) and (c).
all (a), (b) and (c).
The following plot gives the saturated humidity (He) versus temperature (T).Line joining (H1, T1) and (H2, T2) is the constant enthalpy line. Choose the correct one from among the alternatives A, B, C and D. The following plot gives the saturated humidity (He) versus temperature (T).Line joining (H1, T1) and (H2, T2) is the constant enthalpy line. Choose the correct one from among the alternatives A, B, C and D. https://www.indiabix.com/_files/images/chemical-engineering/mass-transfer/335-677-1.png
T1-Dew point temp; T2-Dry bulb temp; T3-Wet bulb temp.
T1-Dew point temp; T2-Wet bulb temp; T3-Dry bulb temp.
T1-Wet bulb temp; T2-Dry bulb temp; T3-Dew point temp.
T1-Dry bulb temp; T2-Wet bulb temp; T3-Dew point temp.
T1-Dry bulb temp; T2-Wet bulb temp; T3-Dew point temp.
When both the fluids flow concurrently in an absorber, the slope of the operating line is
- ve
(+) ve
1
-1
- ve
The percentage humidity is less than the relative humidity only at __________ percent humidity.
zero
hundred
both zero and hundred
none of these
both zero and hundred
Back-trapping in a distillation column
increases tray efficiency.
decreases tray efficiency.
reduces pressure drop.
is desirable, as it provides improved vapour-liquid contact.
decreases tray efficiency.
Back-trapping decreases TE
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.
less than
more than
same as
very much less
more than
Milk is dried usually in a __________ dryer.
freeze
spray
tray
rotary
spray
At a given equilibrium pressure, with increase in temperature, the concentration of adsorbed gas on solid adsorbant
increases
decreases
remains unchanged
increases exponentially
decreases
Which of the following adsorbent is used to decolourise yellow glycerine?
Silica gel
Alumina
Fuller’s earth
Activated carbon
Activated carbon
In a distillation column, with increase in the reflux ratio, the heat removed in the cooler
increases.
decreases.
remains unaffected.
and the heat required in reboiler decreases.
increases.
Pick out the wrong statement.
Constant pressure distillation can not separate an azeotropic mixture.
Relative volatility of a binary mixture changes appreciably with the minor change in temperature.
The relative volatility of a binary mixture at azeotropic composition is unity.
Flash distillation is practised on wide spread scale in petroleum refinery.
Relative volatility of a binary mixture changes appreciably with the minor change in temperature.
Which of the following is not a unit of mass transfer co-efficient?
Moles transferred/(time)(area)(mole fraction)
Moles transferred/(time)(area)(pressure)
Moles transferred/(time)(area)(mass A/mass B)
None of these
None of these
The falling rate period in the drying of a solid is characterised by
increase in rate of drying.
increasing temperatures both on the surface and within the solid.
decreasing temperatures.
none of these.
increasing temperatures both on the surface and within the solid.
In which of the following unit operations, the selectivity is an important parameter?
Distillation
Solvent extraction
Absorption
None of these
Solvent extraction
Which of the following is an undesirable characteristic for the solvent used in gas absorption?
Low vapor pressure
Low viscosity
High gas solubility
None of these
None of these
Which of the following equipments is not used for liquid dispersion?
Wetted wall towers
Packed towers
Venturi scrubers
Agitated vessels
Agitated vessels
Diameter of raschig rings used in packed tower in industry is normally around __________ inches.
2
8
12
18
2
The diffusion co-efficient in m2 /s. of acetic acid in benzene (liquid in liquid) is
2.09 x 10-4
2.09 x 10-5
2.09 x 10-9
2.09 x 10-12
2.09 x 10-9
AAB9 acetic acid in benzene 10^-9
Pick out the wrong statement.
The Reynolds analogy for mass transfer is given by Lewis relation and is applicable, when Schmidt number is one.
Sherwood number for flow in pipes can be expressed as the ratio of the concentration gradient at wall to the overall concentration difference.
According to film theory for equimolar counter diffusion, the mass transfer coefficient is given by sqrt(DAB)(b)P - 3, Q - 2
The z-component of the total mass flux of a component A in binary mixture of A and B is given by - Dab’.dCA/dz.
According to film theory for equimolar counter diffusion, the mass transfer coefficient is given by sqrt(DAB)(b)P - 3, Q - 2
wrong according to film theory sqrt(DAB)…
In case of non-ideal gases and liquids, the molal diffusivity
varies inversely as the pressure.
varies directly as the pressure.
is independent of pressure.
is equal to the volumetric 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
p > > P
p < P
p < < P
p = P
__________ number indicates the ratio of the rates of the heat and mass transfer incase of a cooling tower.
Sherwood
Stanton
Lewis
Peclet
Lewis
The expression, y(1 - x)/x(1 - y) is for
absorption factor
relative volatility
selectivity
Murphree efficiency
relative volatility
In physical terms, Schmidt number means
thermal diffusivity/mass diffusivity.
thermal diffusivity/momentum diffusivity.
momentum diffusivity/mass diffusivity.
mass diffusivity/thermal diffusivity.
momentum diffusivity/mass diffusivity.
In case of liquids, the binary diffusivity is proportional to (where, T = temperature)
T
√T
T^2
1/T
T
binarydiffusivity 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
Newtonion liquids
non-Newtonion liquids
ideal gases
real gases
ideal gases
Mass transfer co-efficient is directly proportional to DAB0.5, according to __________ theory.
penetration
surface renewal
film
none of these
penetration
Sand is dried in foundaries in a___drier.
rotary
fluidised bed
vacuum
spray
fluidised bed
Which of the following employs an accessory known as ‘drift eliminator’?
Multiple effect evaporator.
Mechanical draft cooling tower.
Rotary dryer.
Rotating disc contactor.
Mechanical draft cooling tower.
Pick out the correct statement.
Higher hold up of the solid in the rotary dryer results in better exposure of the solids to the gas.
The ‘Hatta number’ is important in problems involving gas absorption without chemical reaction.
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.
Total reflux in case of distillation operation requires infinite number of plates for a binary system separation.
For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both components is linear in the case of steady state equimolal counter-diffusion.
Pick out the correct statement.
For identical gas flow rates, less pressure drop occurs through a plate tower than through a packed tower.
Plate column can handle greater liquid loads without flooding than packed column, but the liquid hold up is more in the case of plate column.
For the same duty, plate columns weigh less than packed columns.
all (a), (b) and (c).
all (a), (b) and (c).
Humid volume is the total volume in m3 of 1 kg of
vapour laden gas at 1 atm. and room temperature.
gas plus its accompanying vapour at 1 atm. and room temperature.
gas plus its accompanying vapour at 1 atm. and gas temperature.
vapour laden gas at 1 atm. and gas temperature.
gas plus its accompanying vapour at 1 atm. and gas temperature.
humid volume gas plus gas temperature
Diameter to height ratio for a rashig ring is
1
0.5
2
8
1
1 rashig
The equipment used in the extraction of highly corrosive radio active liquids is
pulse column
spray column
mixer settler
baffle tower
pulse column
Advantage of continuous drying over batch drying is that the
drying cost per unit weight of dried product is less.
product with more uniform moisture content is produced.
equipment size required is smaller.
all ‘a’, ‘b’ & ‘c’
all ‘a’, ‘b’ & ‘c’
With increase in temperature, the rate of extraction in leaching (solid-liquid extraction system)
increases
decreases
remains unaffected
increases linearly
increases
In a packed bed absorption column, the channelling will be noted by the
increase in flow rate.
sharp drop in pressure drop.
sharp rise in pressure drop.
none of these.
sharp drop in pressure drop.
Gaseous diffusivity at atmospheric pressure is of the order of __________ cm2/second.
1
1 to 5
5 to 10
> 10
1
In liquid-liquid extraction, the number of phases at plait point is
1
2
3
4
1
In a liquid-liquid extraction, 10 kg of a solution containing 2 kg of solute C and 8 kg of solvent A is brought into contact with 10 kg of solvent B. Solvent A and B are completely immiscible in each other whereas solute C is soluble in both the solvents. The extraction process attains equilibrium. The equilibrium relationship between the two phases is Y* = 0.9X, where Y* is the kg of C/kg of B and X is kg of C/kg of A. Choose the correct answer.
The entire amount of C is transferred to solvent B.
Less than 2 kg but more than 1 kg of C is transferred to solvent B.
Less than 1 kg of C is transferred to B.
No amount of C is tranferred to B.
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)
KL2.DA
KL2/DA
KL/DA2
sqrt(KL2.DA)
If Rm is the minimum reflux ratio, the optimum reflux ratio may be around __________ Rm.
1.2 to 1.5
2.5 to 3
3 to 4
5
1.2 to 1.5
During dehumidification of unsaturated air wet bulb temperature & partial pressure of vapor are not constant. However, during evaporative cooling process with recirculated water supply, the __________ remains constant.
wet bulb temperature
partial pressure of water vapor
relative humidity
none of these
wet bulb temperature
In case of absorption, both the operating and equilibrium lines will be straight for
isothermal operation.
dilute solutions.
dilute solutions and isothermal operation.
none of these.
dilute solutions and isothermal operation.
Mass transfer co-efficient varies as DAB0.5, according to the __________ theory.
film
surface renewal
penetration
none of these
surface renewal
For an absorber, both equilibrium and operating line will be straight for
concentrated solution and non-isothermal operation.
dilute solution and non-isothermal operation.
dilute solution and isothermal operation.
concentrated solution and isothermal operation.
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
0.5
0.6
1
2
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.
humidified at constant wet bulb temperature.
dehumidified.
none of these
humidified with wet bulb temperature decreasing.
Humid volume, at a given temperature is a/an __________ function of humidity.
inverse
exponential
linear
logarithmic
linear
The Schmidt number which is defined as, u/rho D, is the ratio of the
momentum diffusivity to the mass diffusivity.
thermal diffusivity to the mass diffusivity.
momentum diffusivity to the thermal diffusivity.
none of these.
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
f < 1
f > 1
0 < f < 1
f = 1
Perforated plate towers are unique for solvent extraction because, they provide
higher contact area.
better contact of the phase.
repeated coalescence & redispersion of the drop phase.
none of these.
repeated coalescence & redispersion of the drop phase.
In case of absorption & stripping, the interface of the liquid & gas phases are present in equilibrium, when the diffusional resistance of __________ is zero.
interface
gas phase
liquid phase
all ‘a’, ‘b’ & ‘c’
interface
Pick out the wrong statement pertaining to the analogy between equations of heat and mass transfer operations.
Sherwood number in mass transfer is analogous to Nusselt number in heat transfer.
Prandtl number in heat transfer is analogous to Schmidt number in mass transfer.
Reynolds number in mass transfer is analogous to Grashoff number in heat transfer.
Reynolds number remains the same in both heat and mass transfer.
Reynolds number in mass transfer is analogous to Grashoff number in heat transfer.
The slope of the operating line for a single component co-current absorber when plotted in terms of mole ratio units is
0
infinite
(-) ve
(+) ve
(-) ve
The individual mass transfer co-efficients (moles/m2 . s) for absorption of a solute from a gas mixture into a liquid solvent are, KL = 4.5 and KG = 1.5. The slope of the equilibrium line is 3. Which of the following resistance (s) is (are) controlling?
liquid side
gas side
interfacial
both liquid and gas side
gas side
Pore size of the molecular seive 5A is __________ mm.
5
0.5
0.05
50
0.5
Swenson-Walker crystalliser is a __________ unit
continuous
batch
semi-batch
cooling (adiabatic)-cum-evaporation
continuous
SWC Swenson-Waler 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.
5
9
12
28
12
ln{[0.99/(1-0.99)] * [(1-0.02)/0.02]} / ln(2) = 12.25
Absorption (liquid-gas system) with evolution of heat as compared to isothermal absorption results in
decreased solute solubility.
large minimum liquid to gas (L/G) ratio.
large number of trays.
all (a), (b) and (c).
all (a), (b) and (c).
With increase in temperature, the mutual solubility of two liquids
increases
decreases
remains unchanged
decreases exponentially
increases
Pick out the wrong statement.
In solvent extraction, the distribution co-efficient should be as large as possible for solvent economy.
With increase in pressure, the solubility of gases in solvent increases at a fixed temperature.
Decrease in Murphree plate efficiency is an indication of entrainment in distillation column.
The capacity of a distillation coloumn is maximum at total reflux.
The capacity of a distillation coloumn is maximum at total reflux.
wrong capacity maximum at total reflux
The relative volatility of a binary mixture at the azeotropic composition is
1
> 1
0
infinite
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
only vapor phase follows Raoult’s law.
only liquid phase obeys Dalton’s law.
liquid phase obeys Dalton’s law and vapor phase obeys Raoult’s law.
Vapor phase obeys Dalton’s law and liquid phase obeys Raoult’s law.
Vapor phase obeys Dalton’s law and liquid phase obeys Raoult’s law.
Bound moisture is that liquid which exerts an equilibrium vapor pressure __________ that of the pure liquid at the given temperature.
less than
more than
equal to
either (o) or (b); depends on the solid
less than
Lewis number (Le) is
Sc / Pr
Pr x St
Sh x Pr
St x Sh
Sc / Pr
Which of the following is not a continuous leaching equipment?
Pachuka tank
Kennedy extractor
Bollman extractor
Hydrocyclones
Pachuka tank
__________ extractor is used for the concentration of radioactive nuclear waste.
Pulsed column
Sieve plate
Mixer-settler
Ballman
Pulsed column
Moisture content of a substance when at equilibrium with a given partial pressure of the vapour is called the __________ moisture.
free
unbound
equilibrium
bound
equilibrium
All moisture in a non-hygroscopic material is the __________ moisture.
free
equilibrium
unbound
bound
unbound
Pick out the correct relationship. (where, Ri = internal reflux ratio Ro = external reflux ratio.)
(1 + Ro) = Ro/Ri
(1 - Ro) = Ro/Ri
(1 + Ri) = Ro/Ri
(1 - Ri) = Ro/Ri
(1 + Ro) = Ro/Ri
Separation of __________ employs gaseous diffusion process.
N2 and O2 from air
isotopes of uranium
isotopes of helium
SO2 and air
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.
is computed from the intercept of the operating line.
cannot be computed.
is the optimum reflux ratio.
is computed from the slope of the upper operating line that is tangent to the equilibrium curve.
The interfacial area per unit volume of dispersion, in a gas-liquid contactor, for fractional hold up of gas = 0.1 and gas bubble diameter = 0.5 mm is given by (in m2/m3)
500
1200
900
800
500
Though, theoretically the adsorption & desorption isotherms is expected to coincide but sometimes at least a part of the isotherms does not coincide and this phenomenon is known as adsorption hysterisis. In such cases, the desorption equilibrium pressure is __________ that obtained for adsorption.
lower than
higher than
same as
either same or higher than
lower than
adsorption hysterisis lower than
Experimental determination of __________ is done by wetted wall column method.
diffusion co-efficient
mass transfer co-efficient
NTU
none of these
mass transfer co-efficient
wetted wall mass transfer co efficient
Pick out the wrong statement:
Absorption factor is constant, when the equilibrium and operating lines are straight.
In case of a stripper, the equilibrium curve is always below the operating line.
In case of an absorber, the operating line is always above the equilibrium curve.
In the absorption of low solubility gases, the liquid film is the controlling resistance.
In case of a stripper, the equilibrium curve is always below the operating line.
In liquid extraction, if the selectivity is unity, then
separation of the constituents is the most effective.
no separation will occur.
amount of solvent required will be minimum.
solvent flow rate should be very low.
no separation will occur.
Paper industry employs __________ driers.
cylinder
rotary
spray
fluidised bed
cylinder
Which of the following has the same dimension as mass diffusivity?
Momentum flux
Kinematic viscosity
Thermal diffusivity
Both (b) and (c)
Both (b) and (c)
Pick out the wrong statement pertaining to the cooling towers.
In case of induced draft cooling tower, the fan is placed at the top of the tower.
Effectiveness of forced draft cooling tower is reduced by the recirculation of the humid and hot discharged air.
A natural draft cooling tower is recommended to be used, when the air humidity is low and air temperature is also low.
Effectiveness of a mechanical draft cooling tower is reduced with increase in air wet-bulb temperature.
Effectiveness of a mechanical draft cooling tower is reduced with increase in air wet-bulb temperature.
Experiments were conducted to determine the flux of a species A in a stagnant medium across a gas-liquid interface. The overall mass transfer co-efficient based on the liquid side for dilute systems for the above was estimated to be 4 x 10-3 kg mole/m2.s. The equilibrium data for the system is given as y = 2x. The flux across the interface (in kg mole/m2 .s) for bulk concentrations of A in gas phase and liquid phase as y = 0.4 and x = 0.01 respectively is
5.6 x 10-4
8.5 x 10-4
5.6 x 10-3
8.5 x 10-3
8.5 x 10-4
Leaching of coarse solid lumps is also termed as
decoction
dissolution
percolation
agitation and settling
percolation
The main reason for dividing a tall packed tower into series of small towers is to
minimise the overall pressure drop.
avoid flooding.
reduce liquid hold up.
avoid channeling.
avoid channeling.
Co-current absorbers are usually used when the gas to be dissolved in the liquid is
sparingly soluble
highly soluble
a pure substance
a mixture
a pure substance
co-current pure substance
At what percentage (by volume) of alcohol composition, it forms an azeotrope with water?
90
91.5
95
99
95
Measurement of the interfacial area of mass transfer is achieved easily & accurately in case of a __________ coloumn.
spray
packed
bubble cap plate
wetted wall
wetted wall
With the lowering of equiliDrium pressure, at a given temperature, the amount of ad-sorbate on the adsorbent
increases.
decreases.
remains same.
either (a) or (b), depends on the system.
decreases.
Mass transfer co-efficient is defined as
Flux = Co-efficient/concentration difference.
Co-efficient = Flux/concentration difference.
Flux=concentration difference/co-effi-cient.
none of these.
Co-efficient = Flux/concentration difference.
When an unsaturated air-water mixture is heated at constant pressure, then
the partial pressure of water vapour increases.
the specific humidity decreases.
The relative humidity increases.
the relative humidity decreases.
the relative humidity decreases.
During sensible cooling process
relative humidity decreases
relative humidity increases
wet bulb temperature decreases
both (b) and (c)
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.
100
0
50
between 0 and 100
0
In case of physical adsorption, the difference between heat of adsorption and heat of normal condensation is
equal to the heat of formation of surface compound.
equal to the heat of wetting.
zero.
called integral heat of adsorption.
equal to the heat of wetting.
Pick out the wrong statement:
Change in barometric pressure does not affect the relative humidity.
In case of a packed tower, the operating velocity is about half of the flooding velocity, generally.
Elution’ means the desorption of the adsorbed solute by a solvent.
The equilibrium moisture content of the solid can be reduced by increasing the absolute humidity.
The equilibrium moisture content of the solid can be reduced by increasing the absolute humidity.
The value of L/mG ratio for economical absorption operation ranges from
0.5 to 0.8
0.8 to 1.2
1.25 to 2.0
2.5 to 3.5
1.25 to 2.0
Large scale usage of flash distillation is practised in
soap manufacturing
ammonia synthesis plant
polymerisation industry
petroleum refinning
petroleum refinning
High pressure at the bottom of a distillation tower handling heat sensitive materials results in
thermal decomposition of bottoms.
increased relative volatility.
erosion of the tower.
very efficient operation.
thermal decomposition of bottoms.
Alcohol is dehydrated using __________ distillation.
extractive
azeotropic
steam
molecular
azeotropic
Separation of two volatile liquids by distillation makes use of their
selectivity
relative volatility
solubility
density difference
relative volatility
Which of the following increases during evaporative cooling process with recirculated water supply?
Wet bulb temperature
Relative humidity
Partial pressure of vapour
Both (b) and (c)
Both (b) and (c)
Dried finished product sampled from various parts of a __________ dryer exhibits non-uniformity in the moisture content.
rotary
tray
freeze
none of these
tray
__________ is used as an ‘entrainer’ for the separation of acetic acid-water mixture by distillation.
Furfural
Benzol
Butyl acetate
Hexane
Butyl acetate
Rotary dryers cannot handle __________ materials.
free flowing
dry
sticky
granular
sticky
Pick out the correct statement.
Diffusivity decreases with increase in temperature.
Diffusivity increases with increase in molecular weight.
Diffusivity increases with the size of the individual molecule.
none of these.
none of these.
An example of elution is
separation of uranium oxide from its ore by H2SO4 in a Pachuca tank.
separation of sugar from sugar beet by hot water.
dissolution of tannin out of tree barks by water.
recovery of vegetable oils from seeds.
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
mole fractions
mole ratios
partial pressure
mass fractions
partial pressure
Relative volatility does not change appreciably with the change in
temperature
vapour pressure of either component
total pressure
none of these
temperature
Boiling point diagram is not affected by the ambient
pressure
humidity
temperature
both (b) and (c)
both (b) and (c)
The dew point of a saturated gas phase equals the __________ temperature.
gas
room
wet bulb
none of these
gas
dew point - sat gas - gas temp
A solid material shows case hardening properties while drying. Which of the following should be controlled to control the drying process?
Flow rate of inlet air
Relative humidity of outlet air
Humidity of inlet air
Temperature of the solid
Temperature of the solid
In case of liquid-liquid binary diffusion, diffusivity of one constituent into another is not dependent on the
temperature and pressure
concentration
nature of the constituents
none of these
none of these
For continuous drying of grannular or crystalline material, the dryer used is the __________ dryer.
tunnel
tray
rotary
none of these
rotary
When adsorption hysteresis is observed, the desorption equilibrium pressure is __________ that obtained by adsorption.
always lower than
always higher than
same as
dependent on the system; can be either lower or higher than
always lower than
Moisture in a substance exerting an equilibrium vapour pressure less than that of pure liquid at the same temperature is called the __________ moisture.
bound
unbound
critical
none of these
bound
For a binary mixture with low relative volatility, continuous rectification to get pure products will require
low reflux ratio
less number of trays
small cross-section column
high reflux ratio
high reflux ratio
The efficiency of a plate column will be maximum, when the flow is ideal __________ the plate.
across
above
both (a) & (b)
neither (a) nor (b)
both (a) & (b)
Heat load in a cooling tower
means the amount of heat thrown away (KCal/hr.) by the cooling tower.
is equal to the number of kg, of water circulated times the cooling range.
both (a) & (b).
neither (a) nor (b).
both (a) & (b).
In case of absorption with exothermic reaction, for fluids having
Pr = Sc; percentage change in heat and mass transfer flux will be the same for a given change in the degree of turbulence.
Pr = Sc = 1; total mass, momentum and thermal diffusivity will be the same.
both (a) and (b)
Pr = Sc ; there won’t be any change in heat and mass transfer flux with changes in degree of turbulence.
both (a) and (b)
Detergent solution is dried to a powder in a
spray dryer
spouted bed dryer
tunnel dryer
pan open to atmosphere
spray dryer
Which of the following mixtures does not form an azeotrope at atmosheric pressure?
Water-alcohol
Methyl alcohol-acetone
Butyl acetate-water
None of these
None of these
During bottling of cold drinks (e.g. Pepsi), the main resistance to mass transfer for the absorption of carbon dioxide in water lies in the
gas film
liquid film
liquid-gas interface
none of these
liquid film
The overall mass transfer co-efficient for the absorption of SO2 in air with dilute NaOH solution can be increased substantially by
increasing the gas film co-efficient.
increasing the liquid film co-efficient.
increasing the total pressure.
decreasing the total pressure.
increasing the gas film co-efficient.
Flooding results in
high tray efficiency
low tray efficiency
high gas velocity
good contact between the fluids
low tray efficiency
For the air water system under ambient conditions, the adiabatic saturation temperature and the wet bulb temperature are nearly equal, because
water has a high latent heat of evaporation.
Lewis number is close to unity.
they are always equal under all circumstances.
solubility of the components of air in water is very small.
water has a high latent heat of evaporation.
In an operating distillation column, the
vapors and liquids are at their dew point and bubble point respectively
driving force for the liquid flow is its specific weight.
driving force for the vapor flow is the pressure drop, as the pressure decreases gradually from the bottom to the top of the column.
highest temperature is encountered at the top of the column.
driving force for the vapor flow is the pressure drop, as the pressure decreases gradually from the bottom to the top of the column.
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
range is 15 F.
approach is 10 F.
both (a) & (b).
neither (a) nor (b).
both (a) & (b).
The diffusivity (D) in a binary gas mixture is related to the temperature (T) as
D is proportional to T
D is proportional to T^0.5
D is proportional to T^1.5
D is proportional to T^2
D is proportional to T^1.5
For which of the following unit operations, Lewis number is of significance?
Adsorption
Binary distillation
Gas absorption
Humidification
Humidification
Tray spacing in a distillation column of dia 10-12 ft. used in petroleum refinery may be around __________ inches.
5
30
60
100
30
If a1 and a2 are the relative volatilities when the pressure in the distillation column is 1 and 2 atm respectively. Pick out the correct statement.
a1 = a2
a1 = 2a2
a1 = 0.5 a2
none of these
none of these
a1 a2 none of these
The dimension of diffusivity is same as that of the
density
molal concentration
kinematic viscosity
velocity head
kinematic viscosity
The temperature to which a vapour gas mixture must be cooled (at varying humidity) to become saturated is called the __________ temperature.
dew point
wet bulb
dry bulb
none of these
none of these
Entrainer used in azeotropic distillation should
form a low boiling azeotrope with one of the constituents of the mixture.
form a new azeotrope of low relative volatility with one of the constituents of the mixture.
have high latent heat of vaporisation.
have high viscosity to provide high tray efficiency.
form a low boiling azeotrope with one of the constituents of the mixture.
In case of steam distillation, the steam leaving the liquid is not completely saturated with distillate vapour, because
temperature is less.
total pressure is less.
mixing of steam with the material being vaporised is not so intimate as to result in equilibrium condition.
saturated steam is used for steam distillation.
mixing of steam with the material being vaporised is not so intimate as to result in equilibrium condition.
Pick out the wrong statement.
The operating line always lies above the equilibrium solubility curve in case of a single component absorber.
The operating line always lies below the equilibrium solubility curve in case of a single component stripper.
The operating pressure in solvent extraction system should be below vapor pressures of all components.
The solubility of a particular gas in ideal solution in any solvent is always the same.
The operating pressure in solvent extraction system should be below vapor pressures of all components.
Leaching of coffee from coffee beans is done by
hot water
hexane
lime water
dilute H2SO4 (hot)
hot water
For contacting a highly soluble gas with a liquid
bubble the gas through liquid.
spray the liquid on gas stream.
either (a) or (b) would suffice.
none of these.
bubble the gas through liquid.
During drying operation, it is easier to remove the __________ moisture.
equilibrium
critical
unbound
bound
unbound
With increase in solvent rate, the number of transfer units, NtoG, for a fixed degree of absorption from a fixed amount of gas
increases
decreases
decreases linearly
remains unaffected
decreases
Ion exchange process is similar to
absorption
adsorption
extraction
leaching
adsorption
A distillation column with N plates is being operated under normal conditions. At some point of time, the operation is shifted to total reflux condition (i.e., no product and residue are being withdrawn and feed to the column is stopped). At the new steady state,
composition of vapors and that of liquid do not vary throughout the column.
reboiler load and condenser load are minimum.
the top and bottom compositions are unchanged with and without total reflux.
the top and bottom compositions correspond to the maximum enrichment available.
the top and bottom compositions correspond to the maximum enrichment available.
Dryer widely used in a textile industry is __________ dryer.
festoon
cylinder
conveyor
tunnel
conveyor
Solvent used in extractive distillation
changes the relative volatility of the original components.
should be of high volatility.
should form azeotropes with the original components.
all (a), (b) and (c)
changes the relative volatility of the original components.
Air at a particular humidity is heated in a furnace. The new dew point
decreases
increases
depends on the extent of heating
remain unchanged
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)
straight
parallel
both (a) & (b)
neither (a) nor (b)
both (a) & (b)
The vapour pressure exerted by the moisture contained in a wet solid depends upon the
nature of the moisture.
temperature.
nature of the solid.
all (a), (b) and (c).
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
G/mL
mL/G
LG/m
L/mG
Smoke is an example of
solid dispersed in liquid
solid dispersed in gas
liquid dispersed in gas
gas dispersed in liquid
solid dispersed in gas
Which of the following adsorbant is used in the refinning of sugar?
Bone charcoal
Wood charcoal
Silica gel
Activated clay
Bone charcoal
bone sugar
Stacked packing compared to dumped packing
provides poorer contact between the fluids.
gives lower pressure drop.
both (a) and (b).
gives higher pressure drop.
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
minimum
operating
maximum permissible
total
