Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2019 Winter 5th Sem New 2150501 Mass Transfer Operation I Previous Question Paper
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ? V (New) EXAMINATION ? WINTER 2019
Subject Code: 2150501 Date: 25/11/2019
Subject Name: Mass Transfer Operation - I
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) What are the effects of temperature and pressure on diffusivity of gases and
liquids? Justify your answer with suitable equations.
03
(b) Compare Penetration theory with Film theory with reference to molecular
diffusion.
04
(c) A service attendant accidently spills 50 liters of gasoline, which quickly
spreads over a level surface of area 8 m
2
. Estimate the time required for the
gasoline to evaporate into the stagnant air above the surface of the liquid. The
diffusivity of gasoline in air is 0.65 m
2
h
-1
. The air temperature is 298 K.
Evaporation may be assumed to take place through a film of air of 2 m
thickness. Vapour pressure of gasoline at 298 K is 76 mmHg. The density of
gasoline is 720 kg m
-3
and the molecular weight of gasoline is 200. The
operation takes place at 1 atm pressure.
07
Q.2 (a) Classify the mass transfer operations based on direct contact of two
immiscible phases with examples.
03
(b) With the help of Fick?s law of diffusion prove that D AB = DBA. 04
(c) Oxygen (A) is diffusing through carbon monoxide (B) under steady state
condition with carbon monoxide non-diffusing. The total pressure is 1?10
5
N/m
2
and temperature is 0
o
C. The partial pressure of oxygen at two planes 2.0
mm apart is respectively 13000 and 6500 N/m
2
. The diffusivity for the
mixture is 1.87?10
-5
m
2
/s. Calculate the rate of diffusion of oxygen in kmol/s
through each square meter of the two planes.
07
OR
(c) Oxygen is diffusing through a stagnant layer of methane 5 mm thick. The
temperature is 20?C and the pressure 100 kN/m
2
. The concentrations of
oxygen on the two sides of the film are 15% and 5% by volume. The
diffusivity of oxygen in methane at 20?C and 100 kN/m
2
is 2.046 x 10
-5
m
2
/s.
Calculate: (a) Rate of diffusion of oxygen in kmol/ m
2
s. (b) What will be the
rate of diffusion if total pressure is raised to 200 kN/m
2
, other conditions
remaining unaltered?
07
Q.3 (a) Compare distillation and liquid-liquid extraction operation. 03
(b) Establish any two analogies between Mass transfer and Heat transfer
operations using dimensionless numbers.
04
(c) During absorption of carbon tetrachloride from a mixture of air-CCl4 by an
organic oil, the gas and liquid phase mass transfer coefficients have been
estimated to be 0.32 and 5.26 kmol/(hr)(m
2
)(mol fraction), respectively. The
equilibrium relation under the operating conditions is given by y
*
= 20 x,
where y and x are mole fractions of CCl4 in gas and liquid phases respectively.
Estimate the overall mass transfer coefficients, Ky, and Kx.
07
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ? V (New) EXAMINATION ? WINTER 2019
Subject Code: 2150501 Date: 25/11/2019
Subject Name: Mass Transfer Operation - I
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) What are the effects of temperature and pressure on diffusivity of gases and
liquids? Justify your answer with suitable equations.
03
(b) Compare Penetration theory with Film theory with reference to molecular
diffusion.
04
(c) A service attendant accidently spills 50 liters of gasoline, which quickly
spreads over a level surface of area 8 m
2
. Estimate the time required for the
gasoline to evaporate into the stagnant air above the surface of the liquid. The
diffusivity of gasoline in air is 0.65 m
2
h
-1
. The air temperature is 298 K.
Evaporation may be assumed to take place through a film of air of 2 m
thickness. Vapour pressure of gasoline at 298 K is 76 mmHg. The density of
gasoline is 720 kg m
-3
and the molecular weight of gasoline is 200. The
operation takes place at 1 atm pressure.
07
Q.2 (a) Classify the mass transfer operations based on direct contact of two
immiscible phases with examples.
03
(b) With the help of Fick?s law of diffusion prove that D AB = DBA. 04
(c) Oxygen (A) is diffusing through carbon monoxide (B) under steady state
condition with carbon monoxide non-diffusing. The total pressure is 1?10
5
N/m
2
and temperature is 0
o
C. The partial pressure of oxygen at two planes 2.0
mm apart is respectively 13000 and 6500 N/m
2
. The diffusivity for the
mixture is 1.87?10
-5
m
2
/s. Calculate the rate of diffusion of oxygen in kmol/s
through each square meter of the two planes.
07
OR
(c) Oxygen is diffusing through a stagnant layer of methane 5 mm thick. The
temperature is 20?C and the pressure 100 kN/m
2
. The concentrations of
oxygen on the two sides of the film are 15% and 5% by volume. The
diffusivity of oxygen in methane at 20?C and 100 kN/m
2
is 2.046 x 10
-5
m
2
/s.
Calculate: (a) Rate of diffusion of oxygen in kmol/ m
2
s. (b) What will be the
rate of diffusion if total pressure is raised to 200 kN/m
2
, other conditions
remaining unaltered?
07
Q.3 (a) Compare distillation and liquid-liquid extraction operation. 03
(b) Establish any two analogies between Mass transfer and Heat transfer
operations using dimensionless numbers.
04
(c) During absorption of carbon tetrachloride from a mixture of air-CCl4 by an
organic oil, the gas and liquid phase mass transfer coefficients have been
estimated to be 0.32 and 5.26 kmol/(hr)(m
2
)(mol fraction), respectively. The
equilibrium relation under the operating conditions is given by y
*
= 20 x,
where y and x are mole fractions of CCl4 in gas and liquid phases respectively.
Estimate the overall mass transfer coefficients, Ky, and Kx.
07
2
OR
Q.3 (a) Define the terms : Conning, Weeping and Dumping 03
(b) Name the equipments used in Leaching operation. Discuss any one in brief. 04
(c) 5000 kg/hr of a SO2-air mixture containing 5% by volume of SO2 is to be
scrubbed with 2,00,000 kg/hr of water in a packed tower. The exit
concentration of SO2 is reduced to 0.15%. The tower operates at 1 atm. The
equilibrium relation is given by: Y = 30 X
Y = Mole SO2 / Mole air; X = Mole SO2 / Mole water If the packed height
of tower (Z) is 0.42 m, Calculate the height of transfer unit (HTU).
07
Q.4 (a) Mention different types of packings for gas absorption operation and their
selection criterion.
03
(b) Acetic acid can be recovered from its aqueous solution by extraction using
suitable organic solvent. Various organic solvents are available in market.
Discuss significant criteria for solvent selection.
04
(c) Deduce the following relationships between overall mass transfer coefficients
(represented by
y
K and
x
K ) and individual mass transfer coefficients
(represented by
y
k and
x
k ).
x y y
k
m
k K
'
1 1
? ? and
x y x
k k m K
1
"
1 1
? ?
07
OR
Q.4 (a) With respect to tray tower discuss the function of following parts. 1)
Downspout 2) Weir 3) Demister pad
03
(b) Deduce equitation of solvent to feed ratio for single stage liquid-liquid
extraction.
04
(c) Explain Meir?s super saturation theory of crystallization with neat sketch. 07
Q.5 (a) If 100 kg of a solution of acetic acid (C) and water (A) containing 30% acid
is to be extracted three times with isopropyl ether (B) at 20?C, using 40 kg of
solvent in each stage, determine the quantities and compositions of the various
streams. How much solvent would be required if same final raffinate
concentration were to be obtained with one stage? Use following equilibrium
data.
Water layer Isopropyl ether layer
wt fraction C wt fraction B wt fraction C wt fraction B
0.0069 0.012 0.0018 0.993
0.0289 0.016 0.0079 0.984
0.1330 0.023 0.0482 0.933
0.3670 0.044 0.2160 0.715
0.4640 0.165 0.3620 0.487
14
OR
Q.5 (a) Outline the industrial applications of leaching. 03
(b) List and discuss the factors that affect leaching operation. 04
(c) With a neat sketch explain the working of Swenson Walker Crystallizer. 07
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This post was last modified on 20 February 2020