Jawaharlal Nehru Technological University Hyderabad 2007 B.E Chemical Engineering PROCESS HEAT TRANSFER SET NO 3 - Question Paper

Code No: R05220801 Set No. 3
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 wall has 2 layers of insulation on it. The layers are of equal thickness but
the thermal conductivity of layer one is twice that of the layer 2. How much more
thicker should layer two be if the heat flow is to be decreased by 20%, the total wall
thickness and the driving force remaining un changed. What would be the fractional
reduction in heat flow if the material of layer one is changed by the material of layer
2. [16]
2. Write short notes on:
(a) Log mean temperature difference
(b) Fouling factors
(c) Parallel flow heat exchangers
(d) Counter flow heat exchangers. [16]
3. (a) What do you mean by hydrodynamic and thermal boundary layers? discuss
with reference to flow over a flat heated plate.
(b) Derive an expression for the avg. Nusselt number for turbulent flow over
a flat plate where the transition occurs abruptly when the local Reynolds
number is four × 105. [16]
4. The core of a nuclear reactor consists of parallel vertical plates 2.5m in height
and 1.6 m in width. The reactor is designed on free convection heating of liquid
Bismuth. The maximum surface temperature of the plate can be 990 0C and the
least allowable temperature of bismuth is 336 0C. compute the maximum heat
dissipation rate from the both sides of every plate. Properties of liquid bismuth:
Density = 10005 kg/m3; Specific heat = 148 J/kg 0K; thermal conductivity = 13.1
W/m 0K; Viscosity = 0.865 × 10-3 N-s/m2. [16]
5. (a) In condensate flow, how is the wetted perimeter defined? How does the wet-
ted perimeter various from ordinary perimeter. What is the significance of
calculating wetted perimeter.
(b) How does the presence of a non condensable gas in a vapor influence the
condensation heat transfer. [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) Write briefly the methods of feeding in multiple effect evaporators.
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Code No: R05220801 Set No. 3
(b) Write on the capacity, economy, effect of liquid head and boiling point elevation
with respect to multiple effect evaporators. [16]
8. Consider a 20 cm diameter spherical ball at 8000K suspended in the air. Assuming
that the ball closely approximates black body, determine
(a) the total black body emissive power
(b) the total amount of radiation emitted by the ball in five min and
(c) the spectral black body emissive power at a wavelength of three µm. [16]
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Earning:   Approval pending.