The following
figure depicts steady one-dimensional diffusion of water vapour from the
surface of water taken in a conical flask at room temperature. Derive the
governing equation for determining the concentration profile of water vapour in
the gas medium. Neglect change of level of water due to condensation. The
temperatures of the gas and the liquid media are identical and constant.
GATE
2007
Answer: (A)
If TA
and TB are the boiling points of pure A and B respectively and TAB
is that of a non homogeneous immisible mixture of A and B, then
(A)
TAB<TA and TB
(B)
TAB>TA and TB
(C)
TA>TAB>TB
(D)
TB>TAB>TA
GATE
2007
Answer: (A)
In a
distillation operation, it is desired to have a very high purity bottom
product. Initially, a kettle-type reboiler is used at the bottom of the column
and the following analytical equation is used to obtain the equilibrium trays
in the exhausting section of the column.
Where
xm is the composition of the liquid leaving tray m. Tray m is the
last equilibrium tray obtained by a McCabe Thiele graph of the exhausting
section. If the kettle-type reboiler is replaced by a thermo-syphon reboiler,
the analytical equation, for the exhausting section will be
GATE 2007
Answer: (C)
A 50 cm × 50 cm
× 1 cm flat wet sheet weighing 2 kg initially, was dried from both the sides
under constant drying rate period. It look 1000 secs for the weight of the
sheet to reduce to 1.75 kg. Another 1 m × 1 m × 1 cm flat sheet is to be dried
from one side only. Under the same drying rate and other conditions, time
required for drying (in secs) from initial weight of 4 kg to 3 kg is
(A)
1000
(B)
1500
(C)
2000
(D)
2500
GATE
2007
Answer: (C)
It is desired to
reduce the concentration of pyridine in 500 kg of aqueous solution from 20
weight percent to 5 wt percent in a single batch extraction using chlorobenzene
as solvent. Equilibrium compositions (end points of the tie line) in terms of
weight percent of pyridine-water-chlorobenzene are (5, 95, 0) and (11, 0, 89). The
amount of pure solvent required in kg for the operation is
(A)
607
(B)
639
(C)
931
(D)
1501
GATE 2007
Answer: (B)
Benzene in an
air-benzene mixture is to be reduced from 5.2 mol% in the feed to 0.5 mol% by
contacting with wash oil in a multistage countercurrent gas absorber. The inlet
flow rate of air-benzene mixture is 10 mol/s while benzene free wash oil comes
in at 9.5 mol/s. If the equilibrium curve is given as Y* = X, where Y* and X
are equilibrium mole ratios of benzene in air and benzene in oil, the number of
equilibrium stages required to achieve the above separation is
(A)
12
(B)
10
(C)
8
(D)
6
GATE 2007
Answer: (B)
Given
the following statements listed from P to T, select the correct combination of
TRUE statements from the choices that follow this list.
(P) Plate columns are preferred when the
operation involves liquids containing suspended solids.
(Q) Packed towers are preferred if the
liquids have a large foaming tendency.
(R) The pressure drop through packed towers
is more than the pressure drop through plate columns designed for the same duty
(S) Packed columns are preferred when large
temperature changes are involved in distillation operations.
(T) Packed towers are cheaper than plate
towers if highly corrosive fluids must be handled.
(A)
T, S, P
(B)
P, Q, T
(C)
S, R, T
(D)
R, Q, S
GATE 2007
Answer: (B)
If
the percentage humidity of air (30°C, total pressure 100 kPa) is 24% and the
saturation pressure of water vapour at that temperature is 4 kPa, the percent
relative humidity and the absolute humidity of air are
(A)
25.2, 0.0062
(B)
25, 0.0035
(C)
20.7, 0.0055
(D)
18.2, 0.0035
GATE
2007
Answer: (A)
Common data for
the next three questions
A binary distillation column separates
100 mol/h of a feed mixture into distillate D and residue W. The McCabe-Thiele
diagram for this process is given below. The relative volatility for the binary
system is constant at 2.4
The distillate and residue flow rates
(in mol/h) are
(A)
D = 48.4, W = 51.6
(B)
D = 51.6, W = 48.4
(C)
D = 54.7, W = 45.3
(D)
D = 45.3, W = 54.7
GATE
2006
Answer: (A)
The ratio of liquid to vapour molar flow
rates in the rectifying section is
(A)
0.64
(B)
1.00
(C)
1.55
(D)
1.80
GATE
2006
Answer: (A)
The minimum number of theoretical stages
(inclusive of reboiler) for this process is
(A)
5.2
(B)
6.1
(C)
7.8
(D)
Infinite
GATE
2006
Answer: (C)
A saturated vapour is fed to a
distillation column at 180 kmol/h. Both the rectifying and stripping section of
the column operate at 60% of their respective flooding velocities. The flooding
velocity of the rectifying section is twice that of the stripping section. The
assumptions of constant molar overflow and constant molar vapour density
throughout the column are valid. If the boil-up rate is 60 kmol/h, then the
relationship between the diameters of the rectifying section (dr)
and the stripping section (ds) is
GATE
2006
Answer: (A)
Experiments conducted with a sparingly
dissolving cylinder wall in a flowing liquid yielded the following correlation
for the Sherwood number
Sh
= 0.023(Re)0.83(Sc)1/3
Assuming the applicability of the
Chilton-Colburn analogy, the corresponding correlation for heat transfer is
(A)
St = 0.023(Gr)0.83(Pr)1/3
(B)
Sh = 0.023(Re)0.83(Pr)1/3
(C)
Jh = 0.023(Re)0.83(Pr)2/3
(D)
Nu = 0.069(We)0.5(Pr)4/3
GATE
2006
Answer: (B)
A drug tablet of mass M0
administered orally at time t = 0 reaches the intestine at time t = τ without
losing any mass. From the intestine, the drug is absorbed into blood. The rate
of absorption is found to be proportional to the mass of the drug in the
intestine with the proportional constant k. Assuming no drug is lost from the
blood, the total mass of the drug in the blood Mb at time t ≥ τ is
given by
(A)
Mb = M0[1-exp{-k(t-τ)}]
(B)
Mb = M0[1-exp{-kτ)}]
(C)
Mb = M0[exp{-k(t-τ)}]
(D)
Mb = M0[1-exp{-k(t+τ)}]
GATE
2006
Answer: (C)
100
mol of a binary mixture F containing 60 mol% A (more volatile) and 40% B is
treated in a batch distillation still. After 1 h, 70 mol of the distillate are
collected leaving behind the residue W. Relative volatility α is 2. The
governing equation is
Log(FxF/WxW)
= α log[{F(1-xF)}/{W(1-xW)}]
The average mole fraction of A in the
distillate is
(A)
0.43
(B)
0.61
(C)
0.69
(D)
0.73
GATE
2006
Answer: (C)
In a multistage counter current
isothermal stripping column, the feed containing 0.05 mol of solute/mol solute
free oil is treated with steam. The absorption factor A = 0.65. The equilibrium
relation is given by Y* = 2X, where Y* and X refer to the
equilibrium mole ratio in the steam and oil phases respectively. The Kremsen
equation is given as follows (‘0’ refers liquid inlet at the top, NP
refers to the last stage at the bottom).
If the steam is initially free of solute
and its exit molar ratio (mol solute/mol steam) is 0.0624, then the number of
equilibrium stages required is
(A)
4.2
(B)
5.2
(C)
7.2
(D)
8.2
GATE
2006
Answer: (B)
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