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Posted By: murali Member Level: Silver Posted Date: 01 May 2008
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2007 Jawaharlal Nehru Technological University B.E Chemical PROCESS HEAT TRANSFER SET NO 1 Question paper
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Code No: R05220801 Set No. 1
II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2007
PROCESS HEAT TRANSFER
(Chemical Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. Explain the following:
(a) Conduction
(b) Free Convection
(c) Forced convection
(d) Radiation. [16]
2. (a) Explain with a neat labeled sketch the single pass tubular condenser.
(b) Draw the temperature length curves for the condenser and explain. [10+6]
3. Lubricating oil is flowing through a tube having 12.5 mm inside diameter. Oil enters
at 75 0C and leaves at 50 0C. Tube surface is maintained at 45 0C. The velocity of
oil through the tube is 2.4 m/s. Calculate the length of the tube required for the
cooling operation. Properties of oil : Density = 860 kg/m3; thermal conductivity
= 0.14 w/ m 0K; Specific heat = 1780 J/kg 0K. Assume that flow is fully developed
laminar. Average Nusselt number is 3.66 [16]
4. (a) Determine the hydraulic radius for the following cross sections
i. Circular tube of diameter D and
ii. Square tube of dimensions, SxS.
(b) A steam pipe 0.05m diameter and 2.5m long has been placed horizontally
and exposed to still air at 25 0C. If the pipe wall temperature is 295 0C,
determine the rate of heat loss. At the mean temperature of 160 0C, the
thermo physical properties of air are: Thermal conductivity is 0.036 w/m 0K;
Kinematic viscosity is 30.09 × 10-6m2/s; Pr = 0.682; For laminar flow over
horizontal cylinders within the range, 103 < (Gr Pr) < 109; Use Nu = 0.53
(Gr Pr)0.25. [16]
5. (a) Write a note on radiation in film boiling
(b) Explain drop wise and film condensation [16]
6. Cold water enters a counter flow heat exchanger at 10 0C at a rate of 8 kg/s, where
it is heated by a hot water stream that enters the heat exchanger at 70 0C at a rate
of 2 kg/s. Assuming the specific heat of water to remain constant at Cp = 4.18
kJ/kg 0C, determine the maximum heat transfer rate and the outlet temperatures
of the cold and the hot water streams for this limiting case. [16]
1 of 2
Code No: R05220801 Set No. 1
7. 0.15 kg/s of a 10% caustic soda liquor is to be concentrated to 20% strength in a
single effect evaporator. The unit is a forced circulation type in which the liquor
is pumped through the vertical tubes of the calendria. Tubes are of 35mm outside
diameter, 30 mm inside diameter and 1.5 m in length. Steam supplied for heating
is a saturated one having saturation temperature of 110 0C. Boiling point rise of
the solution is 3 0C.The unit operates under vacuum at 13 kN/m2 (52 0C). The
overall heat transfer coefficient is 1750 W/m2 0K. Suggest a suitable thermal design
of the evaporator. [16]
8. A radiation shield that has the same emissivity on both sides is placed between two
large parallel plates, which are maintained at uniform temperatures of 6500K and
4000K and have emissivities of 0.6 and 0.9 respectively. Determine the emissivity
of the radiation shield if the radiation heat transfer between the plates is to be
reduced to 15 % of that without the radiation shield. [16]
? ? ? ? ?
2 of 2
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