Jawaharlal Nehru Technological University Hyderabad 2007 B.E Chemical Engineering PROCESS HEAT TRANSFER SET NO 4 - Question Paper

Code No: R05220801 Set No. 4
II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2007
PROCESS HEAT TRANSFER
(Chemical Engineering)
Time: three hours Max Marks: 80
ans any 5 ques.
All ques. carry equal marks
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1. A slab consists of 2 plates of various material joined together. The total Thick-
ness of the slab is known, but not the individual thickness of the plates. Assuming
that the properties of the materials are known, discuss how and experiment mea-
suring the total heat flux through the slab for a provided temperature difference across
it could be used to determine the unknown dimensions. [16]
2. (a) In a parallel flow double pipe heat exchanger, the hot fluid enters the heat
exchanger at 90 0C and leaves at 50 0C, while the cold fluid enters the heat
exchanger at 20 0C and leaves at 40 0C. compute the LMTD.
(b) In a counter current double pipe heat exchanger, the hot fluid enters at 200
0C and leaves at 100 0C, while the cold fluid enters the heat exchanger at 20
0C and leaves at 80 0C. compute the LMTD. [8+8]
3. Water at a rate of 0.015 kg/s is heated from 20 0C to 48 0C in a steel tube of 25
mm diameter. Steam is used for heating and it condenses on the outer surface of
the tube. Wall temperature is maintained at 108 0C. The flow is fully developed.
compute the value of heat transfer coefficient and the length of the tube needed.
[16]
4. (a) What is hydrodynamic and thermal boundary layers. Illustrate with reference
to flow over a heated flat plate. describe boundary layer thickness.
(b) Derive the formula for Reynold’s analogy. Write the formula for Colburn
analogy and Dittus Boelter formula. [16]
5. At a low overall
T the boiling heat flux for a tube bundle is about four times that
for a single tube, but at a high
T the flux is much lower than that for a single
tube. provide a logical explanation of the difference. [16]
6. Glycerine (Cp = 2400 J/kg 0C) at 20 0C and 0.3 kg/s is to be heated by ethylene
glycol (Cp = 2500 J/kg 0C) at 60 0C and the identical flow rate in a thin walled double
pipe parallel flow heat exchanger. If the overall heat transfer coefficient is 240 W/
m2 0C and the heat transfer surface area is 7.6 m2, determine
(a) the rate of heat transfer and
(b) the outlet temperature of the glycerine and the glycol. [16]
7. (a) Classify the kinds of evaporators with industrial application.
(b) discuss the long vertical tube evaporator with a neat sketch. [16]
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Code No: R05220801 Set No. 4
8. The temperature of the filament of an incandescent light bulb is 25000K. Assuming
the filament to be a black body, determine the fraction of the radiant energy emitted
by the filament that falls in the visible range. Also, determine the wave length at
which the emission of radiation from the filament peaks. [16]
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Earning:   Approval pending.