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7/21/2019 Mass Transfer Design question paper
1/11
UNIVERSITI
TEKNOLOG
P
ETRONAS
FINAL
EXAMINATION
SEPTEM
BER
2012
SEM
ESTER
COURSE
:
CCB2053
MASS
TRANSFER
DESIGN
DATE
: 29th DECEMBER
2012
(SATURDAY)
TIME
:
9.00 AM
-
12.00
NOON
(3
HOURS)
INSTRUCTIONS
TO
CANDIDATES
1.
Answer
ALL
questions from the Questions
Booklet.
2. Begin
EACH
answer
on a new
page
in the Answer
Booklet.
3.
lndicate
clearly answers
that are
cancelled,
if any.
4. Where applicable,
show clearly steps
taken in arriving at the
solutions and indicate
ALL assumptions.
5. Do not
open
this
Question
Booklet
until instructed.
6.
Engineering
Data Formulae
Booklet
is
provided.
Note
:
There
are
ELEVEN
(11)
pages
in this
Question
Booklet
including
the
cover
page
and
Appendix.
Universiti
Teknologi
PETRONAS
7/21/2019 Mass Transfer Design question paper
2/11
1.
CCB 2053
a.
Explain
TWO
(2')
types of
mass transfer
and
gives
TWO
(2)
examples
for each
type of
mass
transfer.
[4
marks]
b.
Ammonia
(NHs)
gas
is diffused
through a layer
of nitrogen
(N2) gas
at
298
K and 1 atm
pressure.
The
partial pressure
of ammonia
at
one
point
is 0.133
atm
and
at the
other
point
20
mm
away
it
is
0.066 atm. The
diffusivity
of the
mixture
is
2.30
x 10-5
m2ls.
.
Calculate
the flux
of
NH3
in
kgmol/s,m2
with
non-diffusing
Nz
at
one boundary.
[4
marks]
ii.
Repeat
part
(i)
assuming
Nz
also diffuses
and the
flux
is
eq uimolar
cou
nterdiffusion.
[3
marks]
iii.
Based
on the mass flux
obtained
in
part
(i)
and
(ii),
which
conditions
give
the
highest
flux? Explain
your
answer.
[3
marks]
7/21/2019 Mass Transfer Design question paper
3/11
c.
CCB
2053
flash separator
which
IGURE
Q1
shows
an
adiabatic
equilibrium
indicates
all
variables
in
each stream.
F
zi
TF
Pf
L
xi
il
TL
P,
FIGURE
Q1:
Adibatic
Equilibrium
Flash
Separator
Compute
the degrees
of
freedom
using
the Gibbs
phase
rule.
[3
marks]
might
be
specified
to
solve
the
above
[3
marks]
What
variables
problem?
7/21/2019 Mass Transfer Design question paper
4/11
ccB2053
a.
Give
THREE
(3)
reasons
why
an
economic
tradeoff
exists
between the
number
of trays
and
the reflux
ratio.
[3
marks]
b.
A continuous
distillation
column
operating
at
1
atm
is
to be
designed
for
separating
an ethanol-water
mixture.
The feed
is 20
mol%
ethanol
and
the
feed
flow
rate
is
1000
kgmol/h
of
saturated liquid.
A
distillate
composition
of
80
mol% ethanol
and
bottoms
composition
of not
more
than
2
mol%
ethanol
is desired.
The
reflux ratio
is
5/3. Equilibrium
data for ethanol-
water
system
at
1
atm are
given
in
TABLE
e3.
TABLE
Q3:
Equilibrium
data
of
ethanol
in
ethanol-water
system
Temperature
("c)
Molpercent
of
ethanol
in the liquid
phase,
x
Molpercent
of
ethanol
in
the
gas
phase,
y
100.0
0.00
0,00
95,5
1.90
17.00
89.0
7.21
38,91
86.7
9.66
43.75
84 1
16.6't
50.89
82.7
23.37
54.45
82.3
26.08
55.80
80.7
39.65
61.22
79.7
51.98
65.99
78.7
67.63
73.85
78.1
89.43 89.43
78.3
100.00
100.00
7/21/2019 Mass Transfer Design question paper
5/11
ccB2053
i.
calculate
the amount
of
distillate
and bottom
products
in
kgmol/h.
[4
marks]
ii.
By
using
the
graphical
McCab-e-Thiele
method,
determinethe
number
of
theoretical
stages
required.
[6
marks]
iii. Estimate
the
minimum
reflux
ratio.
[3
marks]
iv.
lf the
feed
condition changes
to saturated vapour
condition, discuss
the differences
in
the
number
of theoretical
stages.
[4
marks]
7/21/2019 Mass Transfer Design question paper
6/11
a.
b.
CCB
2053
Using
a
suitable diagram,
show
the
operating line for
minimum
liquid
flow
of absorption
process
and
the operating line
for minimum
gas
flow of a stripping process.
Justify
your
answers.
[4
marks]
A
packed
tower 4,0
m
tall
is
used
to
absorb
ethyl
alcohol
from
an
inert
gas
by
90 kgmol/h
of
pure
water
at
303K
and 101.3 kPa.
The
total
gas
stream
flowrate
of
100
kgmol/h
contains 2.a
moP/o
alcohot
and the
exit
concentration
is 0.20
mol%.
The
equilibrium
relation is
y
:
mx
:
0.68x for this dilute
stream.
i. Calculate
the mol
fraction
of
ethyl
alcohol in
the ext liquid.
[4
marks]
I
ill
Using
the
analytical
equations,
calculate
the
theoretical
trays,
y'/.
tv.
Determine
the HETP
for
the
above absorption
proess.
[4
marks]
Show
the
relationship
between
the number
of
theoretical
trays
obtained
n
part
(ii)
and
the number
of
transfer unit
obtained
in
part
(iii)
by
using suitable
graphical
explanation.
[4
marks]
7/21/2019 Mass Transfer Design question paper
7/11
a
.
CCB 2053
distillation
for
certain
n
general,
extraction
applications.
I
0
0.69
1.41
2.89
6.42
13.30
25.50
36.70
45.30
46.40
s
preferred
over
Define
the
liquid-liquid
extraction
process
and
over
distillation,
b.
i.
state
TWo
(2)
requirements
for liquid-liquid
extraction
to
be
feasible.
[2 marks]
An
aqueous
feed
of
200
kg/h
containing
25
wt% acetic
acid is
being
extracted
by
pure
isopropyl
ether
at
the
rate of
600 kg/h
in a
counter-current
multistage
system.
The
exit
acid concentration
in
the
aqueous
phase
is to
contain
3 wt%
acetic acid.
The
riquid-riquid
equilibrium
data at 25oC
and
1 atm
are
presented
in TABLE
e4.
TABLE
Q4: Liquid-liquid equilibrium
data
for
acetic
acid
(A)-
water
(W)-
isoproppyl
ether
(E)
system
at2SoC
and
1
atm.
Water
layer
lsopropyl
ether layer
wt%(A)
wt%(W)
wt%(E)
wt%(A)
wt%(W)
wt%(E)
0
0.6
99.4
0.18
0.5
99.3
0.37
its
importance
[2
marks]
98.9
98.4
97.1
84.7
71.5
98.9
98.1
97.1
95.5
91.7
84.4
71.1
58.9
45.1
37.1
1.2
1.2
1.5
1.6
1,9
2.3
3.4
4.4
9.6
16.5
0.7
0.79
0.8
1.93
1.0
11.40
3.9
21.60
6.9
4.82
1.9
93.3
31.10
10.8
58.1
36.20
15.1
48.7
7/21/2019 Mass Transfer Design question paper
8/11
&
7/21/2019 Mass Transfer Design question paper
9/11
5.
CCB 2053
A
continuous
countercurrent
multistage
system
is
to be
used
to leach
oil
from
a
meal
by
benzene
solvent.
The
process
is
to
treat
2000 kg/h
of
an
inert
solid meal (B)
containing
800
kg
oil (A) and
also
50
kg
benzene
(c),
The
inert flow
per
hour
in
the fresh
solvent
mixture
contains
1310
kg
benzene
and 20
kg
oil. The
leached
solids
are
to contain
ea
kg oil.
The
leaching
process
is in
the
condition
of constant
underflow
of
N
=
1.85
kg
solid/kg
solution.
a.
Plot
the
equilibrium
data on
a Ponchon-savarit
diagram
using
the
graph paper
provided.
[4
marks]
b.
usng
the
graph
in
part
(a),
determine
the
weight
fraction
of or,
yy
leaving
the
stream.
[4
marks]
c.
calculate
the
amount
of
underflow
slurry,
L,
trd in
the ovelow,
v,
leaving
the
stream.
d.
Determine
the number
of
stages
required
for
the
process.
-END
OF
PAPER-
I
7/21/2019 Mass Transfer Design question paper
10/11
Constants
Gas
constants,
R;
=
8314
m3Pa /kg
'K'mol
=
83.145 cm3
barlK.mol
=
82.055 cm3
atm/K.mol
CCB
2053
Conversion
factors
T(K)
=
tf
C)
+
Zts
1
atm
=
760
torr
=
101325
Pa
l
bar
=
1OsPa
=
0.9869 atm
1 liter
=
1
dm3=
1O0O cm3
APPENDIX
Equatons:
1.
General
diffusion
and convection
No:
-cD*+.9o(*^+trr)
azc
J
o
=
D
ulP
n' -
p
'l)
Flux
for
equimolarcounter
diffusion
"
RT(r,
-
,,)
2.
Stagnant,
non-diffusing
B
(total
pressure
constant)
:
r
DnuP
tY
.,
-
--ln
RT(2,-Zt)
P-p,qt
3. Rectifying
operating
line:
.R
xD
l'-_-r+_
'
R+l
R+l
5. Absorption
material
balance:
(constant
molar
flow)
{
+-)*
v
(
-z'):
t(
-.,-l
.'
l+,-l
f
l-
r,0, (l- o,)
-
[l-r,,J lt-
y,,)
6. KremserEquation
:
nl
lt
t-
"?u--)r-
)lwhere
ris
Absorption
ractor
i
A,
:
:t-
:
I
Y,
-
ntr,
-'re
ls
ADSorPIlon
ffi
V
r,,
InA
4. Rayleigh:
'idL:
ln
L'
-
f'
d*
Jr
r
J,
,-_t-
L2
^=y-x
10
7/21/2019 Mass Transfer Design question paper
11/11
CCB 2053
^/
_
ln{l(t
-l)
t
All0,,,
-
kx,,y(y,,,,
-
kxi,)l+
(t
l)}
t'oc
-
7. Extraction:
Fraction
of a solute,
i,
absorb
"O:
ffi
8.
Fuller
equation:
/r
_
lo'r'trs(l
lMrrllM)'')
u..18-ffi
11
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