IBX- Mass Transfer 4-6 Flashcards
Boiling point diagram is
not affected by pressure.
affected by pressure.
a plot of temperature vs. liquid composition.
a plot of temperature vs. vapour composition.
affected by pressure.
When acetone is added in a two layer mixture of methyl isobutyl ketone and water at 30°C, the acetone distributes between the two layers and the composition of the layer follows two solubility curves. For this system,
as the acetone concentration increases, the solubility curves approach each other.
both the phases become identical at a particular common point on both the solubility curves called the plait point.
the distribution curve which is a plot between x (acetone concentration in one phase) and y (acetone concentration in other phase) is analogous to x-y curve used in distillation and absorption terminates on the x = y diagonal at the concentration of the plait point.
all (a), (b) and (c).
all (a), (b) and (c).
Steam distillation is used to
reduce the number of plates.
avoid thermal decomposition of a component.
increase the efficiency of separation.
increase the total pressure of distillation.
avoid thermal decomposition of a component.
Freundlich equation applies to the
adsorption of solute from
dilute solutions, over a small concentration range.
gaseous solutions at high pressure.
concentrated solutions.
none of these.
dilute solutions, over a small concentration range.
For ethanol-water system, the lowering of distillate quality from 95% to 92% will cause __________ plate requirement.
no change in theoretical
marginal decrease in the number of
major decrease in the number of
none of these
marginal decrease in the number of
The apex of an equilateral-triangular coordinate (in ternary liquid system) represents a/an
pure component
binary mixture
ternary mixture
insoluble binary system
pure component
The diffusivity (D) in a binary gas mixture is related to the pressure (P) as
D∝P^0.5
D∝ 1/p^0.5
D∝1/p
D∝1/p^1.5
D∝1/p
A slurry is to be dried to produce flaky solid. Which dryer would you recommend ?
Spray dryer
Drum dryer
Rotary dryer
Dielectric dryer
Spray dryer
Which of the following psychrometric processes is followed by water vapour laden unsaturated air, when it is passed through solid or liquid adsorbent ?
Cooling and dehumidification.
Heating and dehumidification at almost constant wet bulb temperature.
Dehumidification with dry bulb temperature remaining constant.
None of these.
Heating and dehumidification at almost constant wet bulb temperature.
In gas-liquid contact operation, the number of ideal stages, N=(xA-xB)/(xb-x^b). This is true when the stripping factor ‘S’ is
S > 1
S < 1
S = 1
S = ∞
S > 1
The cooling effect in a cooling tower can not be increased by
increasing the air velocity over the wet surfaces.
reducing the humidity of entering air.
lowering the barometric pressure.
none of these.
none of these.
The value of NA/(NA + NB) for steady state molecular diffusion of gas ‘A’ through non-diffusing gas ‘B’ is
1
∞
0.5
2
1
The humid volume may be increased by increasing the
temperature at constant humidity.
humidity at constant temperature.
both (a) and (b).
neither (a) nor (b).
both (a) and (b).
Pick out the wrong statement
Co-current absorbers are usually used, when the gas to be dissolved in the liquid is a pure substance.
In case of gas absorption, HETP is equal to HTU, when both the operating line & the equilibrium lines are parallel.
Hatta number is important in case of gas absorption with chemical reaction.
In actual practice, absorption is an en-dothermic process, while stripping is an exothermic process.
In actual practice, absorption is an en-dothermic process, while stripping is an exothermic process.
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.
continuous
steam
azerotropic
none of these
steam
Large scale drying of wheat is done in a __________ dryer.
fluidised bed
spouted bed
tray
vacuum rotary
spouted bed
Azeotropic distillation is employed to separate
constant boiling mixture.
high boiling mixture.
mixture with very high relative volatility.
heat sensitive materials.
constant boiling mixture.
The drying time between fixed moisture content within diffusion controlled ‘falling rate period’ is proportional to (assuming that drying occurs from all surfaces of the solid) (where, T = thickness of the solid )
sqrt(T)
T
T^2
T^3
T^2
At the boiling point of the liquid at the prevailing pressure, the saturated absolute humidity becomes
1
0
∞
none of these
∞
Use of natural draft cooling tower is practised, when the air has low
humidity
temperature
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’
both ‘a’ & ‘b’
Pressure drop through plate tower as compared to that through packed tower, for the same duty will be
less
more
equal
either (a) or (b); depends on the packing height
more
Dimension of mass diffusivity is the same as that of
kinematic viscosity
dynamic viscosity
surface tension
pressure
kinematic viscosity
Dorr thickener is an equipment used for
classification
sedimentation
clarification
leaching
sedimentation
Steam distillation is used to separate
azeotropes.
high boiling substances from nonvolatile impurities.
heat sensitive materials.
mixtures of low relative volatility.
high boiling substances from nonvolatile impurities.
In distillation where q is defined as the moles of liquid flow in the stripping section per mole of feed introduced, for saturated liquid feed
q > 1
q < 1
q = 1
q = 0
q = 1
Which of the following is an undesirable property in a tower packing ?
Large surface per unit volume.
Large free cross-section.
Low weight per unit volume.
Large weight of liquid retained.
Large weight of liquid retained.
Water entrained by circulating air in cooling towers is termed as
drift
blow down
vapor load
none of these.
drift
A 25 cm x 25 cm x 1 cm flat sheet weighing 1.2 kg initially was dried from both sides under constant drying rate conditions. It took 1500 seconds for the weight of the sheet to reduce to 1.05 kg. Another 1m x 1m x 1cm flat sheet of the same material is to be dried from one side only.Under the same constant drying rate conditions, the time required for drying (in seconds) from its initial weight of 19.2 kg to 17.6 kg is
1000
1500
2000
2500
1000
With increase in temperature, the rate of leaching increases, because the
diffusivity of solute increases.
viscosity of solvent decreases.
thermal conductivity of solute increases.
none of these.
diffusivity of solute increases.
Humidity chart is useful for the solution of problems concerning condensation, vaporisation and air conditioning. At a given dry bulb temperature, value of humidity obtained from the humidity chart directly, is in terms of __________ humidity.
molal
relative
percentage
none of these
molal
The Kundsen diffusivity is proportional to (where, T = absolute temperature)
sqrt(T)
T^2
T
T^4
sqrt(T)
In case of constant underflow extraction operation, the __________ at all solute concentration.
solids are drained to the same extent
ratio of the insoluble to solution is constant
both(a) & (b)
neither (a) nor (b)
both(a) & (b)
In an absorption coloumn, the flooding velocity for random packing is __________ that for stacked/regular packing.
greater than
smaller than
equal to
either (a), or (b) ; depends on the type of packing
smaller than
The relation among various mass transfer co-efficients (M.T.C) for ideal gases is given by (where, Kc & Km are M.T.C. for equimolar counter diffusion with concentration & mole fraction respectively as the driving force. and, Kp = M.T.C. for diffusion of a gas through a stagnant inert gas with pressure as driving force.)
Kc = Kp = Km
Kc = Kp/RT = Km . RT/P
Kc = Kp . RT = Km . RT/p
none of these
Kc = Kp . RT = Km . RT/p
With increase in temperature, the leaching rate increases because of the
increased diffusivity.
decreased viscosity of liquid.
both (a) and (b).
neither (a) nor (b).
both (a) and (b).
Leaching of uranium ore and gold ore is done in
centrifugal extractor
Pachuka tanks
Bollman extractor
none of these
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.
increases the scale forming tendencies of water.
is undesirable.
all (a), (b) & (c).
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
decrease in air temperature
increase in air humidity
both (a) and (b)
neither (a) nor (b)
both (a) and (b)
Antibiotics are best handled in a
Podbielniak extractor.
sieve tray contractor.
rotating disc contactor.
pulsed column extractor.
Podbielniak extractor.
The fixed cost of a distillation column at minimum reflux ratio is
minimum
infinite
optimum
none of these
infinite
__________ extractor uses centrifugal force for separating the two phases.
Treybal
Schiebel
Podbielniak
None of these
Podbielniak
In a binary distillation column, if the feed contains 40 mole % vapour, the q line will have a slope of
1.5
-0.6
-1.5
0.6
-1.5
Pick out the wrong statement.
Mechanical agitation is required, if the system has low interfacial tension.
Seive tray towers are generally used for systems having low interfacial tension.
When Henry’s law constant is very small, then the mass transfer rate is controlled by the gas film resistance.
Taylor-Prandtl analogy for heat and mass transfer considers the transfer through both laminar and turbulent layers.
Mechanical agitation is required, if the system has low interfacial tension.
Acetic acid will be most economically separated from a dilute solution of acetic acid in water by
solvent extraction
continuous distillation
evaporation
absorption
solvent extraction
Design calculation for multiple component distillation is done by
Ponchon-Savarit method
Mccabe-Thiele method
enthalpy concentration method
tray to tray calculations.
tray to tray calculations.
To get high tray efficiency
interfacial surface between liquid and gas phase should be large.
time of contact between the two phases should be less.
gas velocity should be very low.
liquid entrainment should be severe.
interfacial surface between liquid and gas phase should be large.
The mass transfer co-efficient for a solid sphere of radius ‘a’ dissolving in a large volume of quiescent liquid, in which D is the diffusivity of solute, is
D/a
D/2a
proportional to sqrt(D)
dependent on the Reynolds number
dependent on the Reynolds number
Pick out the wrong statement. Generally for physical adsorption, a gas of
higher molecular weight is adsorbed in preference to a gas of low molecular weight.
high critical temperature is adsorbed in preference to a gas of low critical temperature.
low volatility is adsorbed in preference to a gas of high volatility.
none of these.
none of these.
In most of the mechanically agitated liquid-liquid extractors, baffles or horizontal compartmental plates are provided, which helps in
reducing the axial mixing.
increasing the rate of extraction.
maintaining the concentration difference between the two phases.
all ‘a’, ‘b’ & ‘c’.
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
Kg=(1/Kg)+(m/Kl)
1/Kg=(1/Kg)+(m/Kl)
1/Kg=(1/Kl)=(m/Kg)
Kg=(1/Kl)+(m/Kg)
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
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.
