Mass Transfer Operations I Jntu Model Paper{Www.Studentyogi.Com}

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Code No: R05310804
Set No. 1
III B.Tech I Semester Regular Examinations, November 2007
MASS TRANSFER OPERATIONS-I
(Chemical Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks

1. Explain in detail the classi cation of mass transfer operations based on the phases
involved. [16]

2. Ammonia is di using through a stagnant mixture containing 1/3 N2 and 2/3 H2 by
volume. The total pressure is 206kN/m2 and temperature of 55 0C. Calculate the
rate of di usion of ammonia through a lm of 0.5 mm thick when the concentrations
of ammonia on either side of the lm are 10% and 5% by volume.
Di usivity of NH3 in N2 at 25 0C is 1.32×10-5 m2 /sec
Di usivity of NH3 in H2 at 250C is 4.1×10-5 m2 /sec.
[16]

3. Discuss the correlation between Sherwood, Schmidt and Reynolds for ow insides
pipes, ow outside tubes parallel to axis, ow normal to cylinders, ow normal to
tube bundle and ow past single spheres. [16]

4. (a) With the help of gure explain what do you mean gas phase controlled mass
transfer coe cient and liquid phase mass transfer coe cient. What is their
relation to local overall mass transfer coe cient? Further, what is the signi -
cance of overall mass transfer coe cient?
(b) Explain the terms operating line, driving force line and equilibrium curve.
[10+6]

5. (a) How is a tall tower supported? What problems may occur if a tall tray or
packed tower has tilted by 5 degrees, say?
(b) Explain how to liquid misdistribution in a packed bed a ects its performance.
Can liquid misdistribution lead to misdistribution of gas too? [8+8]

6. (a) A mixture of benzene and p-xylene is batch distilled at atmospheric pressure.
The rate of heat input to the still is 4000 kcal/h. Individual heats of vapor-
ization are: benzene = 100 kcal/kg, p-xylene = 85 kcal /kg, and the relative
volatility of benzene in the mixture is 5.6. Calculate the instantaneous rate of
vaporization of p-xylene when the liquid in the still has 40 mole% benzene in
it.
(b) Derive Rayleigh’s equation and mention assumptions made. [6+10]

7. A continuous fractionating column operates with re ux ratio 3.5 to separate equimo-
lar mixture of feed of 13600 kg/hr. to get a distillate containing 97% Benzene and
bottoms containing 2% benzene (all wt%). Calculate moles of distillate and residue


Code No: R05310804
Set No. 1
if feed is at its boiling point and number of ideal stages required. The equilibrium
data is as follows. [16]
Mol. Fraction of benzene x 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Mol. Fraction of benzene y 0.21 0.35 0.51 0.64 0.72 0.79 0.86 0.91 0.96

8. (a) Explain brie y choice of the solvent in extractive distillation.
(b) How operating and initial costs changes as re ux ratio increase? Explain.[8+8]


Code No: R05310804
Set No. 2

1. (a) Explain brie y various pressure driven membrane separation process.
(b) Explain brie y separation process where surface phenomena is important with
suitable examples. [10+6]

2. Ammonia gas (A) di uses through nitrogen gas (B) under steady state conditions
with nitrogen non di using. The total pressure is 1.013×105 pa and the temperature
is 298 K the di usion path (z2-z1) is 0.15 m the partial pressure of NH3 at one point
is 1.5×104 Pa the DAB of the mixture at 1.013×105 pa and 298 K is 2.3×10-5 m2
/sec. Calculate

(a) the ux of NH3 and
(b) the equimolar counter di usion ux, assuming that N2 also di uses. [8+8]

3. (a) Describe the basic di erences between Film Theory, Penetration Theory and
Film-surface renewal theory.
(b) Write short notes on analogies between heat and mass transfer. [10+6]

4. Absorption of oxygen from an air bubble o ccurs in ‘pure’ water. Calculate the
overall coe cients Ky and Kx for the following cases:

(a) The two- lm model is applicable. The air- lm thickness is 2 mm, and the
water- lm thickness is 0.02 mm.
(b) The lm model is applicable for the gas-phase. The contact time of a liquid
element with the gas is 1 s. Given: di usivity of O2 in air = 0.176×10-4 m2/s,
in water = 2.1×10-9 m2/s; the equilibrium relation is p = 4.36×104x, p =
partial pressure of O2 in atm; temperature = 298 K; total pressure = 1 atm.
[16]

5. (a) State the various characteristics of tower packings.
(b) What are the two ma jor types of packings? Explain each with neat diagram.
[8+8]

6. Ethanol forms a nearly ideal solution with iso-butanol and has a relative volatility
2.2. A heated feed containing 40 mole% ethanol and 60 mole% iso-butanol enters
a ash drum at rate of 50 kmol/h. prepare the plot of the fractional yield of the
distillate versus its composition. What fraction of the feed should be vaporized in
order to have a bottom product containing not more than 10% ethanol? [16]


Code No: R05310804
Set No. 2
7. An equimolar binary mixture of saturated liquid is to be separated in a packed
distillation column operated at atmospheric pressure. The relative volatility is
1.2. The distillate product to be obtained should contain 95 mole% of the more
volatile component bottom product contains 5 mole% of the more volatile compo-
nent. Compute for this case, the number of transfer units required if the column is
operated at total re ux. [16]

8. (a) In extractive distillation, why is a large concentration of solvent required in
the liquid phase? Why doesn’t the solvent enter the column at the top tray?
In azeotropic distillation, what is the entrainer?
(b) Can a distillation column be operated at total re ux? Explain
(c) Under what conditions should extractive distillation be considered? [8+4+4]


Code No: R05310804
Set No. 3

1. (a) Mention minimum 4 examples for separation processes where mass in sepa-
rating agent.
(b) Explain brie y the Separation process where contact of solid-liquid is involved
with suitable examples.
(c) Explain brie y the Thermal di usion. [4+8+4]

2. Estimate the di usivity of n-Butanol vapor (A) (C2H5CH2CH2OH) through air at 1
atm. Pressure and 59 0C. Data: Molecular weight n-butanol=74; Molecular weight
of air=29. For air B/ =97, rB = 0.3617 nm. Group contribution of atomic volume
(m3/K.atom) C=0.0148 O=0.0074 H=0.0037 and rA = 1.18 1/3. Normal boiling
point of n-butanol=117 0C. Collision function data:
[16]
KT/ f(KT/ )
1 0.72
1.5 0.6
2 0.54

3. Discuss the following Mass Transfer Theories:

(a) Penetration Theory
(b) Film-surface renewal theory.
[16]

4. (a) Jasmone is a high-value product used in perfumery and cosmetic industries.
A suspension of jasmine owers in water is contacted with an organic solvent
to recover the compound. During extraction, the compound di uses from the
aqueous phase to the dispersed organic phase. The individual mass transfer
coe cients are 3.5×10-6 cm/s (organic phase) and 2.7×10-5 cm/s (aqueous
phase). The solute is 175 times more soluble in the organic phase (y = 175x;
y = mole fraction of the solute in the organic phase). The aqueous solution is
dilute and the total molar concentration of the organic phase is 10 kmol/m3.
Calculate the overall mass transfer coe cient Ky. Which phase resistance
controls?

(b) Explain brie y two lm theory with neat sketch. [8+8]

5. Brie y explain the design and importance of tray spacing, tower diameter, down
spot, weirs in tray tower. [16]

6. (a) An ethanol-water mixture containing 36% by weight of ethanol is di erentially


Code No: R05310804
Set No. 3
concentration of 6 mole%. Determine the quantity and composition of the
distillate. Molecular weight of ethanol = 46. The VLE data are:
Mole frac.of Ethanol in Liquid(x) 0.18 0.16 0.14 0.12 0.10 0.08 0.06
Mole frac. of Ethanol in Vapour(y) 0.517 0.502 0.485 0.464 0.438 0.405 0.353

(b) Write short notes on applications of distillation. [12+4]

7. A mixture of 60 mole%A and 40 mole% B is separated in a column to yield 96
mole% A as the top product. Also, 97% of A entering the tower must be recovered
in the distillate. The feed is a saturated vapour. The following concentrations have
been measured by analyzing the liquid and vapour samples around the 6 th tray x6
= 0.55, y6 = 0.72, y7 = 0.63.

(a) What is the local value of the relative volatility of A with respect to B?
(b) How many ideal trays do es the column have? Assume that the relative volatil-
ity remains constant. [16]

8. A feed containing 40 mole percent n-hexane and 60 percent n-octane is fed to a
distillation column as saturated liquid. A re ux ratio of 1.2 is maintained. The
overhead product is 95 percent hexane and the bottoms 10 percent hexane. Draw
H-X-Y diagram from the given data. Also calculate the number of stages if re ux
ratio of 1.4 times minimum is used Equilibrium data is given below. [16]
VLE Data, Mole Fraction Hexane, 1 atm
x (liquid) 0.0 0.1 0.3 0.5 0.55 0.7 1.0
y (vapor) 0.0 0.36 0.70 0.85 0.90 0.95 1.0
Enthalpy-Concentration Data
Mole Fraction Hexane Enthalpy cal/gmol
in the liquid
Sat. Liquid Sat. Vapor
0.0 7000 15,700
0.1 6300 15,400
0.3 5000 14,700
0.5 4100 13,900
0.7 3400 12,900
0.9 3100 11,600
1.0 3000 10,000


Code No: R05310804
Set No. 4

1. Explain brie y various factors that should be considered in the design of plant
involving the di usional operations. [16]

2. (a) A narrow tube is partially lled with a liquid and maintained at constant
temperature. A gentle stream of gas is passing across the open end of the
tube. As the liquid evaporates the level drops slowly. At a given time t, the
level is z from the top. Derive an expression to calculate the value of the
di usivity of the liquid vapor in the gas.

(b) An Arnold cell is used to measure the di usivity of acetone in air at 20 0C
and 100 kPa pressures. At time t=0, the liquid acetone surface is 11 mm from
the top of the tube and after 8 hours of operation the liquid surface drops to
20.5 mm. If the concentration of acetone in air that ows over the tube is
zero, what is the di usivity of acetone in air? At 20 0C the vapor pressure of
acetone is 24 kPa and the density of acetone is 790kg/m3. [8+8]

3. Water is being evaporated into a counter-current stream of air in a wetted-wall
column, 30 mm in diameter. Estimate the evaporative ux of water at a point in
the column where the water temperature is 305 k and the mole fraction of water
vapour in the bulk air is 0.0098. The following data and information are supplied:
air rate (dry basis) =1 Kg/min; air temperature at the lo cation =38 0c; air viscosity
(at 38 0c)=12×10-5 kg/m-s; total pressure =1atm. Vapour pressure of water at
the given temperature is 4.5 kN/m2 the gas phase mass transfer coe cient can be
calculated using the Gilliland and Sherwoo d correlation given by
Sh=0.023(Re)0.8 (Sc)0.33

The Reynolds number of air may be calculated at the bulk condition. [16]

4. (a) Derive an expression to nd local overall gas phase mass transfer co e cient.
(b) What is the necessity of introducing the overall mass transfer coe cient?
[12+4]

5. (a) Explain the phenomena of liquid distribution and redistribution in packed
towers.
(b) What are the factors to be considered for choice between tray towers and
packed towers? [8+8]

6. (a) With the help of the boiling point diagrams explain what is a minimum boiling
azeotrope and maximum boiling azeotrope.


Code No: R05310804
Set No. 4
(b) What is the relative volatility? How is it computed for ideal systems? [10+6]

7. (a) For distillation of an equimolar binary mixture of A and B, the equations of
the operating lines are: Rectifying section: y = 0.663x + 0.32. Stripping
section: y = 1.329x - 0.01317. What is the condition of the feed?
(b) Write short notes on partial condensers. [8+8]

8. (a) Represent use of open steam in distillation graphically.
(b) Derive the equation to calculate the amount of liquid vaporized upon entering
of superheated steam. [8+8]

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Mass Transfer Operations I Jntu Model Paper{Www.Studentyogi.Com}