Mass Transfer Flashcards
1.
Mass transfer rate between two fluid phases does not necessarily depend on the __________ of the two phases.
chemical properties
physical properties
degree of turbulence
interfacial area
chemical properties
2.
In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the molality is
0.50
0.60
2
1
0.50
Fenske equation determines the maximum number of ideal plates.
height of the distillation column.
minimum number of theoretical plates.
optimum reflux ratio.
minimum number of theoretical plates.
The term “cooling range” in a cooling tower refers to the difference in the temperature of cold water leaving the tower and the wet bulb temperature of the surrounding air.
a. hot water entering the tower and the wet bulb temperature of the surrounding air.
b. hot water entering the tower and the c. cooled water leaving the tower.
c. none of these
hot water entering the tower and the cooled water leaving the tower
Which of the following is the most suitable for extraction in a system having very low density difference ?
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
a. raising the temperature.
b. lowering the total pressure.
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:
a. relative volatility is reasonably constant.
b. mixture (to be separated) shows negative deviation from ideality.
c. mixture (to be separated) shows positive deviation from ideality.
d. multicomponent distillation is involved.
relative volatility is reasonably constant.
When the temperature and humidity of air is low, we usually use __________ draft cooling tower.
natural
12.
__________ columns are used for liquid dispersion in a continuous gas phase.
Packed column
Overall efficiency of the distillation column is
a. the ratio of number of ideal plates to actual plates.
b. the ratio of number of actual plates to ideal plates.
c. same as the Murphree efficiency.
d. always more than the point efficiency.
the ratio of number of ideal plates to actual plates.
14.
On addition of solute in the solvent, the __________ of the solution decreases.
boiling point
freezing point
vapour pressure
both (b) and (c)
both (b) and (c)
15.
Which is the controlling factor for a drum drier?
Diffusion
Heat transfer
Both (a) and (b)
Neither (a) nor (b)
Both (a) and (b)
16.
Drying operation under vacuum is carried out to
reduce drying temperature.
17.
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
18.
Separation of two or more components of a liquid solution can not be achieved by
fractional crystallisation
liquid extraction
absorption
evaporation
absorption
Stefan’s law describes the mass transfer by
diffusion
bulk flow
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’
both ‘a’ & ‘b’
At minimum reflux ratio for a given separation
number of plates is infinity.
- Relative humidity is the ratio of the
a. partial pressure of the vapour to the vapour pressure of the liquid at room temperature.
b. partial pressure of the vapour to the vapour
c. pressure of the liquid at gas temperature.
actual humidity to saturation humidity.
d. none of these
partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.
22.
In batch distillation with constant reflux, overhead product composition __________ with time.
decreases
23.
Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the __________ of a fibre.
electrical resistance
24.
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
25.
To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)
a. increase both ‘G’ and ‘S’.
b. decrease both ‘G’ and ‘S’.
c. increase ‘S’ and decrease ‘G’.
d. increase ‘G’ and decrease ‘S’
increase ‘S’ and decrease ‘G’.
26.
The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are same for, NPr = NSc = __________
1
27.
Dew point of a gas-vapour mixture
increases with temperature rise.
decreases with temperature rise.
decreases with decrease in pressure.
increases with increase in pressure.
decreases with decrease in pressure.
28.
In a packed absorption tower, if the equilibrium and operating lines are both straight lines, then the ratio, HETP/HTUOG __________ the absorption factor.
increases with increase in
is one at unity value of
both (a) and (b)
neither (a) nor (b)
both (a) and (b)
29.
Which of the following plays an important role in problems of simultaneous heat and mass transfer ?
a. Lewis number
b. Schmidt number
c. Prandtl number
d. Sherwood number
Lewis number
- In case of an absorber, the operating
a. line always lies above the equilibrium curve.
b. line always lies below the equilibrium curve.
c. line can be either above or below the equilibrium curve.
d. velocity is more than the loading velocity.
line always lies above the equilibrium curve.
As the reflux ratio in a distillation coloumn is increased from the minimum, the
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)
S2/S1
S1/S2
S1 - S2
S1 x S2
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 two pairs of partially miscible liquids ?
0
Which of the following remains constant during sensible cooling process ?
Specific humidity
Partial pressure of vapour
Both (a) and (b)
Neither (a) nor (b)
Both (a) and (b)
Physical absorption is
an irreversible phenomenon.
a reversible phenomenon.
accompanied by evolution of heat.
both (b) and (c)
both (b) and (c)
Which of the following quantities need not be fixed before starting the design of a co-current absorber ?
Heat gain or loss
Flow rate of entering liquid
Flow rate of gas
None of these
Flow rate of entering liquid
- Mass transfer co-efficient of liquid is ________.
affected more by temperature than that for gases.
affected much less by temperature than that for gases.
not affected by the temperature.
none of these.
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 ?
Liquid-liquid extraction
Solid-liquid extraction
Multicomponent absorption with chemical reaction
Multicomponent distillation
Multicomponent distillation.
41.
Which of the following liquid-vapor contacting devices provides maximum contact surface area for a particular duty ?
Sieve plate column
Bubble cap column
Randomly packed column
Wetted wall column
Wetted wall column
The equipment frequently used for adiabatic humidification-cooling operation with recirculating liquid is
spray chamber
Chemisorption (chemical adsorption) is ______.
a. same as “Van der Waals” adsorption.
b. characterised by adsorption of heat.
c. an irreversible phenomenon.
d. a reversible phenomenon.
an irreversible phenomenon.
- Raoult’s law applies to the _______.
all liquid solutions
non-ideal solution only.
non-volatile solute.
solvents.
solvents.
In distillation columns, the number of bubble caps per tray primarily depends upon the _____.
allowable liquid velocity.
allowable gas velocity.
allowable gas and liquid velocities.
feed composition.
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.
Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as
K ∝ D
K ∝D
K ∝ D^1.5
K ∝ D^2
K ∝ D
The McCabe Δ L law states that the
molar heats of vaporisation of components are nearly equal.
linear crystal growth rate depends on the degree of supersaturation.
linear crystal growth rate does not depend on the crystal size.
linear crystal growth rate depends on the crystal size.
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