For a binary mixture of components A and B, NA and NB denote the total molar fluxes of components A and B, respectively. JA and JB are the corresponding molar diffusive fluxes. Which of the following is true for equimolar counter-diffusion in the binary mixture?
(A)
NA + NB = 0 and JA
+JB ≠ 0
(B)
NA + NB ≠ 0 and JA
+JB = 0
(C)
NA + NB ≠ 0 and JA
+JB ≠ 0
(D)
NA + NB = 0 and JA
+JB = 0
GATE
2015
Answer: (D)
Benzene is
removed from air by absorbing it in a non-volatile wash-oil at 100 kPa in a
counter-current gas absorber. Gas flow rate is 100 mol/min, which includes 2
mol/min of benzene. The flow rate of wash-oil is 50 mol/min. Vapour pressure of
benzene at the column conditions is 50 kPa. Benzene forms an ideal solution
with the wash-oil and the column is operating at steady state. Gas phase can be
assumed to follow ideal gas law. Neglect the change in molar flow rates of
liquid and gas phases inside the column.
For this
process, the value of the absorption factor (up to two decimal places) is
___________.
GATE
2015
Answer: 1.02
A spherical
naphthalene ball of 2 mm diameter is subliming very slowly in stagnant air at
25°C. The change in the size of the ball during the sublimation can be
neglected. The diffusivity of naphthalene in air at 25°C is 1.1×10-6
m2/s.
The value of
mass transfer coefficient is B×10-3 m/s, where B (up to one decimal
place) is ________.
GATE
2015
Answer: 1.1
Identify the
WRONG statement amongst the following:
(A)
Steam distillation is used for mixtures
that are immiscible with water
(B)
Vacuum distillation is used for mixtures
that are miscible with water
(C)
Steam distillation is used for mixtures
that are miscible with water
(D)
Vacuum distillation columns have larger
diameters as compared to atmospheric columns for the same throughput
GATE
2015
Answer: (C)
Packed towers
are preferred for gas-liquid mass transfer operations with foaming liquids
because
(A)
In packed tower, high liquid to gas
ratios are best handled
(B)
In packed towers, continuous contact of gas
and liquid takes place
(C)
Packed towers are packed with random
packings
(D)
In packed towers, the gas is not bubbled
through the liquid pool
GATE
2014
Answer: (D)
A spherical
storage vessel is quarter-filled with toluene. The diameter of the vent at the
top of the vessel is 1/20th of the diameter of the vessel. Under the
steady state condition, the diffusive flux of toluene is maximum at
(A)
The surface of the liquid
(B)
The mid-plane of the vessel
(C)
The vent
(D)
A distance 20 times the diameter of the
vent away from the vent
GATE
2014
Answer: (C)
Assuming the
mass transfer coefficients in the gas and the liquid phases are comparable, the
absorption of CO2 from reformer gas (CO2+H2)
into an aqueous solution of diethanolamine is controlled by
(A)
Gas phase resistance
(B)
Liquid phase resistance
(C)
Both gas and liquid phase resistances
(D)
Composition of the reformer gas
GATE
2014
Answer: (A)
Which one of the
following statements is CORRECT for the surface renewal theory?
(A)
Mass transfer takes place at steady
state
(B)
Mass transfer takes place at unsteady
state
(C)
Contact time is same for all the liquid
elements
(D)
Mass transfer depends only on the film
resistance
GATE
2014
Answer: (B)
A spherical ball
of benzoic acid (diameter = 1.5 cm) is submerged in a pool of still water. The
solubility and diffusivity of benzoic acid in water are 0.03 kmol/m3
and 1.25×10-9 m2/s respectively. Sherwood number is given
as Sh = 2.0 + 0.6Re0.5Sc0.33. The initial rate of
dissolution (in kmol/s) of benzoic acid approximately is
(A)
3.54×10-11
(B)
3.54×10-12
(C)
3.54×10-13
(D)
3.54×10-14
GATE
2014
Answer: (B)
A wet solid of
100 kg is dried from a moisture content of 40 wt% to 10 wt%. the critical
moisture content is 15 wt% and the equilibrium moisture content is negligible.
All moisture contents are on dry basis. The falling rate is considered to be
linear. It takes 5 hours to dry the material in the constant rate period. The
duration (in hours) of the falling rate period is ___________.
GATE
2014
Answer: 1.22
A binary distillation
column is operating with a mixed feed containing 20 mol% vapour. If the feed
quality is changed to 80 mol% vapour, the change in the slope of the q-line is
_________.
GATE
2014
Answer: 3.75
The
packing of an existing absorption tower is replaced with a new type of packing.
The height of the packing and the inlet conditions are maintained the same as
before. Tests reveal that the number of transfer units is lower than before.
This indicates that the tower with the new packing, when compared to that with
the old packing, will
(A)
Have a higher rate of absorption of the
solute from the gas stream
(B)
Have a lower rate of absorption of the
solute from the gas stream
(C)
Have the same rate of absorption of the
solute from the gas stream
(D)
Have a lower height of transfer unit
GATE
2013
Answer: (B)
The vapor-liquid equilibrium curve of a
binary mixture A - B, may be approximated by a linear equation over a narrow range
of liquid mole fractions (0.2 < xA < 0.3) as follows
yA
= 1.325xA + 0.121
Here yA is the mole fraction
of A in the vapor. 100 moles of a feed (xAF = 0.28) is batch
distilled to a final residue (xAW = 0.2). Using the Rayleigh
equation, the number of moles of the residue left behind in the distillation
unit, up to 2 digits after the decimal point, is ____________.
GATE
2013
Answer: 66.7
A
wet solid is dried over a long period of time by unsaturated air of nonzero
constant relative humidity. The moisture content eventually attained by the
solid is termed as the
(A)
Unbound moisture content
(B)
Bound moisture content
(C)
Free moisture content
(D)
Equilibrium moisture content
GATE
2013
Answer: (D)
A
crosscurrent cascade of N ideal stages is used to treat a feed stream of molar
flow rate E. The feed stream contains a solute which is to be recovered by a
pure solvent having a molar flow rate S. The solvent is divided equally between
these N stages. The linear equilibrium curve relating the mole fractions x and
y* of the solute in the raffinate and the extract respectively, is given by y*
= m x. Assume dilute conditions. The ratio of the solute mole fraction in the
original feed to that in the exit raffinate stream i. e. (X0/XN)
is given by
GATE
2013
Answer: (A)
A
study was conducted in which water was pumped through cylindrical pipes made of
a sparingly soluble solid. For a given pipe and certain flow conditions, the
mass transfer coefficient kc has been calculated as 1 mm/s using the
correlation
Sh
= 0.025 Re0.6 Sc0.33
If
the velocity of the fluid and the diameter of the pipe are both doubled, what
is the new value of kc in mm/s, up to 2 digits after the decimal
point? _____________
GATE
2013
Answer: 1.15
Common
statement for the next two questions
The vapour liquid equilibrium
relation for an ideal binary system is given by
Here xA and 
are the mole fractions of species A in the
liquid and vapour, respectively. The relative volatility (αAB) is
greater than unity.
The
liquid mole fraction xA at which the maximum difference between the equilibrium vapour mole fraction and
liquid mole fraction occurs is
GATE
2013
Answer: (A)
A
liquid having the composition found in the first part of the linked answer
question, is flash distilled at a steady state to a final liquid mole fraction
of 0.25. If αAB is 2.5, the fraction of the feed vaporized is
(A)
0.08
(B)
0.20
(C) 0.67
(D) 0.74
GATE
2013
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