Page 1 of 3
Name
Reg No
C
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
07 THRISSUR CLUSTER
SECOND SEMESTER M.TECH. DEGREE EXAMINATION APRIL 2018
Chemical Engineering
Process Control
07CH6106 ADVANCED HEAT AND MASS TRANSFER
Time:3 hours Max.Marks: 60
Answer all six questions. Part of each question is compulsory.
Answer either part or part of each question
(Use of standard heat and mass transfer data book may be permitted)
Q.no. Module 1 Marks
1a Explain thermal conductivity. Comment on the variation of thermal conductivity
of solids, liquids and gases with temperature.
4
Answer b or c
b Obtain the expression for temperature distribution and rate of heat transferred
for radial conduction in a hollow cylinder of length L and having inner and outer
radii ri and ro respectively. Let the temperatures at the inner and outer surfaces
of the cylinder be Ti and To respectively. Assume steady state conduction
without generation of heat.
5
c A furnace wall is composed of three layers, 10cm of firebrick (k=1.560
followed by 23 cm of kaolin insulating brick 0.073W/mK), and finally 5 cm
of masonry brick 1.0 W/mK). The temperature at the inner wall surface is
1370 K and the outer surface is at 360 K. What are the temperatures at the
contacting surfaces?
5
Q.no. Module 2 Marks
2a Describe the use of Heisler Charts 4
Answer b or c
b Derive the expressions for temperature distribution and rate of heat flow in a
rectangular long fin of uniform cross section
5
c It is known that oranges can be exposed to freezing temperatures for short
periods of time without sustaining serious damage. Consider a 0.10 m
diameter orange, originally at a uniform temperature of 5 0C, suddenly
exposed to surrounding air at 0C. For a surface coefficient between the air
and orange surface, of 15 W/m2 how long will it take for the surface of the
5
Page 2 of 3
orange to reach 0 0C?
Properties of orange are the following
Density 940 kg/m3
Thermal conductivity 0.47 W/mK
Specific heat 3.8 kJ/kg.K
Q.no. Module 3 Marks
3a Explain thermal boundary layer. 4
Answer b or c
b Discuss the exact analysis of laminar boundary layer over a flat plate 5
c
The velocity and temperature distributions in a pipeline are known to be of the
form
u C1 r C2 r2
C3 C4 r +C5 r2
where C1, C2, C3, C4 and C5 are constants. Obtain an expression for bulk
mean temperature.
5
Q.no. Module 4 Marks
4a Compare the effect of temperature and pressure on diffusivity of gases and
liquids citing appropriate equations.
4
Answer b or c
b Derive expressions for flux in unimolecular diffusion and equimolal counter
diffusion for a binary system.
5
c Derive species continuity equation for a binary system with constant ρDAB. 5
Q.no. Module 5 Marks
5a Define the following dimensionless parameters and discuss their physical
significance
i. Reynolds number ii. Shmidt number iii. Sherwood number
iv. Lewis number v. Stanton Number for mass transfer
5
Answer b or c
b A gas stream at 98 kPa and 300 K is flowing with a velocity of 18 m/sec on the
top surface of a thin flat sheet of volatile solid of length 0.5 whose mass
diffusivity in the gas is 5.98 x 10-6 m2/s. Kinematic diffusivity of the gas is
3 x 10-5 m2/s. If concentration of the diffusing species at the gas-solid interface
is 9 x10-6 kmol/m3, calculate the mass transfer coefficient over the flat plate.
7
Page 3 of 3
c Obtain rate equation for diffusion and reaction taking place in a spherical
pellet.
7
Q.no. Module 6 Marks
6a Explain the boundary layer theory of mass transfer 5
Answer b or c
b State the two resistance theory of interphase mass transfer. Obtain the relation
between overall gas phase mass transfer coefficient and individual film mass
transfer coefficients.
7
c A packed tower has been designed to strip component A from an aqueous
stream into a counter-flowing air stream. At a given plane in the tower, the
concentrations of the two adjacent streams are pA,G 4 x 103 Pa and
4 kgmol/m3 of solution. Under the given flow conditions, the overall gas
mass-transfer coefficient, KG is equal to 2.46 x 10-8 kgmol/m2.s.Pa and 60% of
the resistance to mass transfer is encountered in the gas phase. At the tower's
operating condition of 290 K and 101.3 kPa, the system satisfies Henry's law
with a Henry's law constant of 1400 Pa/(kgmol/m3). Determine the individual
gas-film coefficient kG; the individual liquid-film coefficient kL; the
interfacial gas concentration pAL and the overall liquid mass-transfer
coefficient KL.
7