It takes 6 h to dry a wet solid from 50% moisture
content to the critical moisture content of 15%. How much longer will it take to
dry the solid to 10% moisture content. Under the same drying conditions (the
equilibrium moisture content of the solid is 5%).
(A)
15 min
(B)
51 min
(C)
71 min
(D)
94 min
GATE 2002
Answer: (C)
According to the Fenske equation, what will be the
minimum 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 bottoms fraction containing 98 mol% B? [Assume that the relative
volatility (αAB = 2) does not change appreciably in the column]
(A)
5
(B)
9
(C)
12
(D)
28
GATE 2002
Answer: (C)
The dimensionless group in mass transfer that is
equivalent to Prandtl number in heat transfer is
(A)
Nusselt
number
(B)
Sherwood
number
(C)
Schmidt
number
(D)
Stanton
number
GATE
2002
Answer: (C)
The Reynolds analogy for momentum, heat
and mass transfer is best applicable for
(A)
Gases in turbulent flow
(B)
Gases in laminar flow
(C)
Liquids in turbulent flow
(D)
Liquids and gases in laminar flow
GATE 2002
Answer: (A)
For gas absorption the height of a
transfer unit, based on the gas phase, is given by (G: superficial molar gas
velocity; L: superficial molar liquid velocity; FG: mass transfer
coefficient mol/m2.S; a: interfacial area per unit volume of tower)
(A)
G/FGa
(B)
FG/Ga
(C)
G/FG
(D)
L/FGG
GATE 2001
Answer: (A)
The
Lewis relation for air-water humidification is given by (ky: mass
transfer coefficient of moisture in air; hG: heat transfer
coefficient; Cs: heat capacity of vapour gas mixture)
GATE
2001
Answer: (C)
The
surface renewal frequency in Dankwert’s model of mass transfer is given by (kL:
mass transfer coefficient, m/s)
GATE
2001
Answer: (C)
The
interfacial area per unit volume of dispersion in a gas – liquid contactor for
frictional hold up of gas = 0.1 and gas bubble diameter = 0.5 mm is given by
(in m2/m3)
(A)
500
(B)
1200
(C)
900
(D)
800
GATE 2001
Answer: (B)
For
equimolar counter diffusion from a sphere to a surrounding stationary infinite
medium, the mass flux NAi of the diffusion component A at the
interface is given by NAi = DA(CAi - CAb)/R
where DA is the diffusivity, R the radius of the sphere and CAi
and CAb the molar concentrations of A at the interface and at a
point far away from the sphere. Sherwood number based on the diameter of the
sphere is equal to
(A)
1
(B)
2
(C)
3
(D)
4
GATE 2001
Answer: (B)
In
a single stage extraction process 10 kg of pure solvent S (containing no solute
A) is mixed with 30 kg of feed F containing A at a mass fraction XF
= 0.2. The mixture splits into an extract phase E and a raffinate phase R,
containing A at XE = 0.5 and XR = 0.05 respectively. The total
mass of the extract phase is (in kg).
(A)
6.89
(B)
8.89
(C)
10
(D)
8.25
GATE 2001
Answer: (B)
200
kg of solid (on dry basis) is subjected to a drying process for a period of
5000 s. The drying occurs in the constant rate period with the drying rate as
NC = 0.5×10-3 kg/m2-s. The initial moisture content of
the solid is 0.2 kg moisture /kg dry solid. The interfacial area available for
drying is 4 m2/100 kg of dry solid. The moisture content at the end
of the drying period is (in kg moisture/kg dry solid)
(A)
0.5
(B)
0.05
(C)
0.1
(D)
0.15
GATE 2001
Answer: (C)
The
McCabe ΔL law states that the
(A)
Molar heat of vaporization of components
are nearly equal.
(B)
Linear crystal growth rate depends on
the degree of super saturation
(C)
Linear crystal growth rate does not
depend on the crystal size.
(D)
Linear crystal growth rate depends on
the crystal size.
GATE 2000
Answer: (A)
For
the nth tray (counter from the bottom of a distillation column), the Murphree efficiency
is given by
GATE 2000
Answer: (B)
At
750 K and 1 atm, the approximate value of the Schmidt number for air is
(A)
0.01
(B)
0.1
(C)
1
(D)
10
GATE 2000
Answer: (B)
In
a laboratory test run, the rate of drying was found to be 0.5×10-3
kg/m2 when the moisture content reduced from 0.4 to 0.1 on a dry
basis. The critical moisture content of the material is 0.08 on a dry basis. A tray
dryer is used to dry 100 kg (dry basis) of the same material under identical
conditions. The surface area of the material is 0.04 m2/kg of dry
solid. The time required (in second) to reduce the moisture content of the
solids from 0.3 to 0.2 (dry basis) is
(A)
2000
(B)
4000
(C)
5000
(D)
6000
GATE 2000
Answer: (C)
Consider
a system in which component A is being transferred from a gas phase to a liquid
phase. The equilibrium relation is given by yA = 0.75 xA
where yA and xA are mole fractions of A in gas and liquid
phase respectively. At one point in the equipment, the gas contains 10 mole% A
and liquid 2 mole% A. Gas film mass transfer coefficient ky at this
point is 10 kmol/(kr.m2.ΔyA) and 60% of the resistance is
in the gas film. Calculate the overall mass transfer coefficient in kmol/(hr.m2.ΔyA)
(A)
6
(B)
7
(C)
8
(D)
9
GATE
2000
Answer: (A)
The individual mass transfer coefficients (mol/m2.S)
for absorption of a solute from a gas mixture into a liquid are KL =
4.5 and KG = 1.5. the slope of the equilibrium line is 3. Which of
the following resistance is (are) controlling?
(A)
Liquid side
(B)
Gas side
(C)
Interfacial
(D)
Both liquid and gas side
GATE
2000
Answer: (D)
The absorption factor is defined as
(A)
L/mG
(B)
G/mL
(C)
mL/G
(D)
LG/m
GATE
2000
Answer: (A)
An alkaline solution is used to reduce
the concentration of carbon dioxide in a stream 10% to 0.1% by absorption with
irreversible chemical reaction. The overall number of transfer units based on
gas phase is
(A)
9.21
(B)
4.605
(C)
100
(D)
0.001
GATE
1999
Answer: (B)
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