Jawaharlal Nehru Technological University Hyderabad 2007 B.E Chemical Engineering PROCESS HEAT TRANSFER SET NO 2 - Question Paper

Code No: R05220801 Set No. 2
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) Derive an formula for the temperature distribution in a hollow sphere.
(b) Hot gas at a constant temperature of 400 0C is contained in a spherical shell
(200 mm ID, 50 mm thick) made of steel. Mineral wool insulation (k = 0.06
w/m 0k) of thickness 100 mm is wrapped all around it . compute the steady
rate at which heat will flow out if the outside air is at a temperature of 30
0C. Heat transfer coefficient on the inner surface of the steel shell and on the
outer surface of the insulation is 15 w/ m2 0K. [8+8]
3. Liquid mercury at the rate of 1.5 kg/s, flows through a copper tube having inside
diameter 25mm. Mercury enters the tube at 20 0C and leaves at 30 0C. The tube
surface is maintained at a uniform temperature of 50 0C. Properties of mercury
at avg. temperature are: Density = 13582 kg/m3; thermal conductivity = 8.69
w/m 0K; specific heat = 140 J/kg 0K; compute the tube length needed for the
operation. Use Nu = seven + 0.025 (Re Pr)0.3. [16]
4. What electric power is needed to maintain a 0.076 mm diameter 0.6 m long vertical
wire at 400 0K in an atmosphere of quiescent air at 300 0K. The wire’s resistance
is 0.0118 ohms per meter. Nu = 0.37. thermal conductivity = 0.03003 W/m 0K;
Kinematic viscosity = 20.76 × 10-6m2/s; Pr = 0.697 [16]
5. Water is boiled at a atmospheric pressure by a horizontal polished copper heating
element of diameter D = 5mm and emissivity = 0.05 immersed in water. If the
surface temperature of the heating wire is 350 0C, determine the rate of heat transfer
from the wire to the water per unit length of the wire. Properties of water are :
hfg = 2257 × 103J/kg; density = 957.9 kg/m3; Properties of vapor are: Density of
vapor = 0.441 kg/m3; Cp = 1977 J/kg 0C; Viscosity = 1.73×10-5 kg/m.s.; thermal
conductivity = 0.0357 w/m 0C. [16]
6. What is a regenerative heat exchanger. How does a static kind of regenerative heat
exchanger differ from a dynamic kind. [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. 2
8. Determine the 4 view factors associated with an enclosure formed by 2 very
long concentric cylinders of radii r1 and r2. Neglect the end effects. [16]
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Earning:   Approval pending.