IndiaBIX Chemical Engineering: Mass Transfer Section 3 Flashcards
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
greater degree of separation with a fixed number of trays
increased reboiler load
increased reflux ratio
None of these.
increased reflux ratio
__________ column is the most suitable for achieving the best performance for mass transfer operations involving liquid with dispersed solids.
Watted wall
Packed
Plate
Spray
Plate
Deairation (removal of O2) of water is done by
rectification
absorption
ion-exchange
adsorption
ion-exchange
Make up water is supplied during cooling tower operation to compensate for water losses due to
evaporation
blowdown
entrainment
all (a), (b)&(c)
all (a), (b)&(c)
Pick out the wrong statement.
The mole fraction of solute is directly proportional to the molality of a ‘dilute’ solution.
For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both components is nonlinear in the case of steady state unimolal unidirectional diffusion.
Azeotropes obey Raoult’s law at all temperature.
The relative volatility of a binary mixture at the azeotropic composition is 1.
Azeotropes obey Raoult’s law at all temperature.
A minimum boiling azeotrope is exemplified by
toluene-benzene
acetone-carbon disulphide
water-isobutyl alcohol
none of these
acetone-carbon disulphide
Which of the following solutions will follow Raoult’s law most closely ?
A solution of benzene, toluene and oxylene.
35% solution of camphor in water.
35% solution of NH3 in water.
A solution of polar organic compounds (not of homologs of a series).
A solution of benzene, toluene and oxylene.
Use of raschig rings in place of crushed stones as packing in packed beds (other things being same)
increases pressure drop, increases surface area.
increases pressure drop, decreases surface area.
decreases pressure drop, increases surface area.
decreases pressure drop, decreases surface area.
decreases pressure drop, increases surface area.
Critical humidity of a solid salt means the humidity
above which it will always become damp.
below which it will always stay dry.
both (a) and (b).
above Which it will always become dry and below which it will always stay damp.
both (a) and (b).
The assumption made in Elis method in distillation is that enthalpy concentration lines of vapor and liquid are
parallel
straight
both parallel and straight
neither parallel nor straight
both parallel and straight
As complete saturation of an adsorbent is approached, the differential heat of adsrop-tion approaches
that of normal condensation.
integral heat of adsorption.
zero.
none of these.
that of normal condensation.
Absorption with chemical reaction’ is involved in the removal of
carbon dioxide from gaseous stream using alkaline solution.
benzol from coke oven gas using solar oil/wash oil.
ammonia from coke oven gas using refrigerated water.
tar from coke oven gas in primary gas coolers using chilled water.
carbon dioxide from gaseous stream using alkaline solution.
The-relative volatility for separation of a non-ideal binary mixture by distillation should be
0
1
> 1
< 1
> 1
Pick out the wrong statement:
Reboiler is not used in open steam distillation.
The separation of solutes of different molecular sizes in a liquid solution by use of a suitable membrane is called dialysis.
Freeze drying is used for the drying of fish.
Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.
Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.
In paper industry, paper is dried in a __________ dryer.
tunnel
heated cylinder
conveyor
festoon
heated cylinder
Pick out the wrong statement.
Critical moisture content is not a property of the material itself.
A sharp increase in pressure drop gives an indication of the flooding in a distillation column.
Separation of components is not possible in liquid extraction, if selectivity is unity.
Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.
Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.
Only small amount of evaporation of water produces large cooling effects because of its
large latent heat
low viscosity
small latent heat
none of these
large latent heat
The most common packing used in industrial operations is __________ rings.
raschig
lessing
cross-partition
single spiral
raschig
When the feed to a distillation column is a saturated liquid, slope of the feed line is
zero
unity
infinity
none of these
infinity
Leaching of sugar from sugar beets is done by
hot water
hexane
dilute H2SO4
lime water
hot water
Absorption factor method is used to calculate the number of ideal stages, when
operating line lies above the equilibrium line.
operating line lies below the equilibrium line.
both operating and equilibrium lines are parallel.
pressure drop in the column is very high.
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.
reduce the residence time of solid.
increase the residence time of the solid.
none of these.
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)
(1-f)/f
-(f-1)/f
-1/f
-f/(1-f)
- 1/f
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
the system comprises of partially mis-cible liquids.
the system comprises of miscible liquids.
the system comprises of an azeotrope.
on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.
on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.
The rate of mass transfer is not dependent upon the
degree of dispersion of one fluid in the other.
interfacial surface exposed between the phases.
both (a) & (b).
none of these.
none of these.
At equilibrium the concentration of water in vapour phase (C)in kg/m3 of air space and the amount of water (m) adsorbed per kg of dry silica gel are related by, C = 0.0667m. To maintain dry conditions in a room of air space 100m3 containing 2.2 kg of water vapour initially, 10 kg of dry silica gel is kept in the room. The fraction of initial water remaining in the air space after a long time (during which the temperature is maintained constant) is
0.0
0.2
0.4
1.0
0.4
Dry bulb temperature of unsaturated air is more than its __________ temperature.
dew point
wet bulb
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’
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
0.60
0.24
1
0.72
1
The reciprocal of stripping factor is termed as
selectivity index
relative volatility
absorption factor
Murphree efficiency
absorption factor
Ponchan-Savarit method analyses the fractional equipment based on
enthalpy balance only.
material balance only.
both enthalpy and material balances.
the assumption of constant molaloverflow.
both enthalpy and material balances.
The binary diffusivity in gases at atmospheric conditions is about
10-9 cm/sec
10-1 cm2/sec
10-3 sec/cm
10-4 cm2/sec2
10-1 cm2/sec
Percentage saturation is __________ the relative saturation.
always smaller than
always greater than
not related to
none of these
always smaller than
In case of a desorber (stripper), the
operating line always lies above the equilibrium curve.
operating line always lies below the equilibrium curve.
temperature remains unaffected.
temperature always increases.
operating line always lies below the equilibrium curve.
What is the reflux ratio at total reflux ?
Zero
Infinity
Unity
Data insufficient
Infinity
Under conditions of flooding in packed tower, the gas pressure drop
decreases rapidly
increases rapidly
remains constant
is maximum
is maximum
For achieving rapid drying rate in a spray dryer, the diameter of the particles in the feed should be in the range of __________ microns (1 mm = 1000 microns).
1-5
10-60
200-300
> 500
10-60
For absorbing a sparingly soluble gas in a liquid
gas side mass transfer co-efficient should be increased.
liquid side mass transfer co-efficient should be increased.
liquid side mass transfer co-efficient should be decreased.
mass transfer co-efficient must be kept constant.
liquid side mass transfer co-efficient should be increased.
Channelling in a packed tower results from the
high pressure drop
maldistribution of liquid
non-uniformity of packing
both (b) and (c)
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.
heat of wetting.
differential heat of adsorption.
heat of normal condensation.
integral heat of adsorption.
The minimum number of theoretical plates is required for achieving a given separation in distillation column with
no reflux
total reflux
zero reflux ratio
minimum reflux ratio
total reflux
A good solvent used for absorption should not have very high
viscosity
vapor pressure
freezing point
all (a), (b) & (c)
all (a), (b) & (c)
In a counter-current liquid extractor
both liquids flow at fixed rate.
both liquids can have any desired flow rate.
only one of the liquids may be pumped at any desired rate.
liquid’s flow rate depends upon the temperature and pressure.
only one of the liquids may be pumped at any desired rate.
Which of the following is an undesirable property for an absorbing solvent ?
Low vapour pressure
Low velocity
Low freezing point
None of these
None of these
The wetted wall tower is used to determine
individual mass transfer co-efficient (M.T.C.) in gaseous system.
M.T.C. of individual components in a liquid-liquid system.
M.T.C. of liquid in liquid-gas system.
the overall M.T.C. of the system.
individual mass transfer co-efficient (M.T.C.) in gaseous system.
Weight of 1 m3 of humid air as compared to 1 m3 of dry air, under the same conditions, is
less
more
same
unpredictable
less
Positive deviation from Raoult’s law means a mixture whose total pressure is
greater than that computed for ideality.
less than that computed for ideality.
less than the sum of the vapour pressure of the components.
none of these.
greater than that computed for ideality.
With increase in gas rate, the number of transfer units, NtoG, for a fixed degree of absorption by a fixed amount of solvent
increases
decreases
decreases linearly
remains unaffected
increases
Schmidt number is given by
µ / ÏDAB
Re.Pe
Sh x Pe
Re/Pe
µ / ÏDAB
The caking of crystals can be prevented by
maintaining high critical humidity.
maintaining low critical humidity.
coating the product with inert material.
both (a) and (c)
both (a) and (c)
Prandtl number for water at 20°C is about
7
70
0.7
150.
7
