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Name:
Reg No: C
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
07 THRISSUR CLUSTER
SECOND SEMESTER M.TECH. DEGREE EXAMINATION APRIL 2017
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 Derive the expression for the temperature profile and heat flux for a cylindrical
shell with and without internal generation of heat
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Answer b or c
b A 150 mm thick rectangular concrete roof of a room is made up of concrete
(k=0.68W/moC) and horizontal steel rods of 20mm diameter spaced 100mm
between centres (k=24W/moC). The outer and inner roof surface temperatures are
5oC and 23oC respectively. Find the overall thermal resistance heat flux through
the roof.
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c An orange of 60mm diameter produces heat at the rate of 32 W/m3 while ripening.
Estimate the maximum temperature at the core of orange if the skin is at 20oC.
Thermal conductivity of orange is 0.48W/mK
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Q.no. Module 2 Marks
2a Derive the expression for the temperature profile and heat flux for a fin of uniform
cross sectional area insulated at the end.
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Answer b or c
b A cylindrical horizontal electric heater rod dissipating heat is used to heat water at
25oC in a water bath. The diameter of the rod is 5mm and length is 60cm. Find out the
maximum heat dissipation rate from the heater, if the heater surface temperature is not
to exceed 95oC. Properties of water at 60oC are:
Thermal conductivity 0.72W/m.K
Density 972 kg/m3
Specific heat capacity 4170J/kg.K
Viscosity 0.48x10-3 kg/m.s
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c Calculate the percentage increase in heat transfer, when straight rectangular fins are 5
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added to steam contact surface of a plate in a plate exchanger used for heating water.
The fins are 1.2 mm thick, 10 mm long and spaced 5 mm apart. The convective
coefficients for steam and water are 32 W/m2K and 260 W/m2K respectively. Fin
efficiency for steam side is 0.87
Q.no. Module 3 Marks
3a Discuss the heat transfer phenomena in packed and fluidised beds 4
Answer b or c
b Derive the correlation for convective heat transfer coefficient by approximate integral
analysis of boundary layer
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c Air at 20oC with a uniform free stream velocity of 12m/s is moving parallel to a
smooth flat plate heated to a uniform surface temperature of 100oC. Find the length of
laminar boundary layer on the plate (critical Reynolds number is 5x105), the thickness
of the hydrodynamic and thermal boundary layers at the critical length and the mean
heat transfer coefficient over the portion of the plate covered by the laminar boundary
layer. Properties of air at average temperature 60oC are:
Thermal conductivity 0.03W/m.K
Density 1.07 kg/m3
Specific heat capacity 1.01J/kg.K
Viscosity 18x10-6 kg/m.s
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Q.no. Module 4 Marks
4a Write down the characteristics of diffusivity of solids. 4
Answer b or c
b State and explain different types of mass transfer fluxes. Derive the relation between
NA and JA in a binary mixture of A and B.
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c Derive species continuity equation for a binary System. State the assumptions clearly.
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Q.no. Module 5 Marks
5a Define Thiele modulus and discuss its significance. 5
Answer b or c
b Derive Chilton and Colburn analogy of heat and mass transfer. 7
c Derive rate expression for diffusion with simultaneous first-order irreversible
homogeneous reaction.
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Q.no. Module 6 Marks
6a Obtain the relation between overall mass transfer coefficient KG and the individual
film mass transfer coefficients in case of mass transfer between gas and liquid phases.
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Answer b or c
b Explain the boundary layer theory of mass transfer. 7
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c Dry Air is passed across a flat surface at 300K and 100 kPa. The surface is covered
with a thin film of an organic liquid which gets evaporated into the air stream. The
mass transfer coefficient is estimated to be 1.2 x 10-5 kmol/m2s. Assuming
unidiffusion, determine
a. The mass transfer coefficient ky.
b. The rate of vapourisation of the liquid if the vapour pressure is 10 kPa at 300 K.
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