2019 May CH303-D

B E1128 Pages: 3
Reg No.:_______________ Name:__________________________

APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
FIFTH SEMESTER B.TECH DEGREE EXAMINATION(S), MAY 2019
Course Code: CH303
Course Name: MASS TRANSFER OPERATIONS -I
Max. Marks: 100 Duration: 3 Hours
(Use of heat and mass transfer data book to be permitted. Graph sheet may be provided)
PART A
Answer any two full questions, each carries 20 marks. Marks
1 a) Explain flooding and entrainment in a tray column. (4)

b) i. List and explain 2 dimensionless numbers in mass transfer and its (3)
corresponding numbers in heat transfer
ii. List out the conditions favouring high efficiency in a tray column and mention (3)
the operational difficulties associated with them.
c) In the process of absorption of ammonia in air by water, at certain point in the (10)
absorption tower, the mole fraction of ammonia at the gas liquid interface and in
then bulk liquid were measured to be 5.0 x 10-3 and 8.0 x 10-4 respectively. The
molar flux at this point was 0.035 kmol/m2h. If the diffusivity of ammonia in
water is 2.2 x 10-9 m2/s, determine the mass transfer coefficient kx and the film
thickness, neglecting bulk flow effect. Density of solution may be considered
approximately equal to the density of water.
2 a) Compare plate and packed column performance based on any seven features of (7)
the two.
b) Differentiate between random and regular packing materials in a packed column. (8)
c) A solute is being transferred from gas phase to liquid phase. If the gas film (5)
resistance is double the liquid film resistance, determine the effect of the
following on the rate of mass transfer
i. doubling the gas film mass transfer coefficient
ii. reducing the liquid film mass transfer coefficient to half of its original value
3 a) Explain the film theory of mass transfer (4)
b) Derive expression for the molar flux due to equimolar counter current diffusion of (6)
A and B. Sketch and explain the concentration profile.
c) With the help of a neat diagram explain the general constructional details of a tray (10)
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column.
PART B
Answer any two full questions, each carries 15 marks.
4 a) Derive the equation for operating curve for a counter current absorption tower (4)
b) Define absorption factor and mention its significance (3)
c) i. Illustrate with a neat sketch, the concept of adsorption wave. (4)
ii. Differentiate between wet bulb temperature and adiabatic saturation (4)
temperature. Under what conditions, both become equal?
5 a) Compare the characteristics of physisorption and chemisorption. (4)
b) Write down the classification of cooling towers. (4)
c) Wash oil containing 0.007 kg hexane/kg oil is used in a counter current packed (7)
column absorber to scrub a feed gas stream containing 0.09 kg hexane/kg hexane
free gas mixture. The outlet gas stream contains 0.001 kg hexane/kg hexane free
gas mixture. Determine the height of packed section required to treat 1000
kg/(hr)(m2 of empty tower cross section) of hexane free gas mixture. The
equilibrium relation may be taken as Y=1.5 X where Y and X are solute/non-
solute mole ratio in gas phase and liquid phase respectively. The overall
coefficient Kya may be taken as 350 kg/(hr) (m3) (unit gradient of y). The feed
rate of hexane free wash oil is 5000 kg/(hr)(m2).
6 a) Define overall efficiency, Murphree stage efficiency and Point efficiency of a tray (3)
column
b) Explain four important properties of a good solvent. (4)
c) With the help of a neat diagram describe the working of a spray chamber for (8)
humidification.
PART C
Answer any two full questions,each carries 15 marks.
7 a) Explain the advantages of freeze drying (5)
b) Define critical moisture content (2)
c) Describe the construction and working of a Draft Tube Baffle Crystalliser with a (8)
neat diagram.
8 a) List the assumptions applicable to an MSMPR crystalliser. (5)
b) Define purity and yield with respect to crystallisation. (2)
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c) With the help of a neat diagram, explain the working of a spray drier. (8)
9 a) In the falling rate period, if the rate of drying varies as R = aX + bX2, show that (8)
the time of drying in the falling rate period is given by
b) 1200 kg of a 30%(wt) solution of sodium carbonate in water is cooled slowly to (7)

300K so that 800 kg Na2CO3.10H2O crystallises and a portion of water evaporate
during the process. If solubility of anhydrous sodium carbonate is 25 kg/100 kg
water at 300K, calculate the percentage of water in the feed evaporated.
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Reg No.:_ Name:____________

1 a) Explain flooding and entrainment in a tray column. (4)

the time of drying in the falling rate period is given by

b) 1200 kg of a 30%(wt) solution of sodium carbonate in water is cooled slowly to (7)

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