Download PTU (Punjab Technical University) B.Tech (Bachelor of Technology) / BE (Bachelor of Engineering) 2021 January ME 5th Sem 78247 Heat Transfer Previous Question Paper
Total No. of Pages : 03
Total No. of Questions : 18
B.T ech (Mechanical Engineering) (Se m.?5)
HEAT TRANSFER
Subject Code : BTME-501-18
M.Code : 78247
Time : 3 Hrs. Max. Marks : 60
INST RUCT ION TO CANDIDAT ES :
1 .
SECT ION-A is COMPULSORY cons is ting of TEN questions carrying TWO marks
each.
2 .
SECT ION-B c ontains F IVE questions c arrying FIVE marks eac h and s tud ents
have to atte mpt any FOUR q ues tions.
3 .
SECT ION-C contains THREE questions carrying T EN marks e ach and s tudents
have to atte mpt any T WO questio ns.
SECTION-A
Answer briefly :
1)
What will be your response to a person who states that heat cannot be transferred in
vacuum?
2)
Mention some of the cases where heat is generated internally at uniform rate in the
conducting medium itself.
3)
Enumerate the various assumptions made in the formation of energy equation for one
dimensional heat dissipation from an extended surface.
4)
What are Heisler charts?
5)
Define Nusselt number. How it is related to temperature gradient in the fluid immediately
in contact with the solid surface.
6)
What do you understand by hydrodynamic and thermal boundary layers?
7)
In the design of condensers, which of the two types of condensation is usually selected
and why?
8)
What do you understand by fouling of heat exchanger? How does it affect the
performance of heat exchanger?
9)
Define monochromatic and total emissive power.
10) Define radiosity and irradiation.
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SECTION-B
11) Starting from the differential element, establish the following expression for loss of heat
from a lagged pipe per m2 of metal surface per degree temperature difference between the
metal and lagging surfaces
k
q
r log
R / r
e
Where k is thermal conductivity of lagging material, R and r are the radii of lagging and
metal surfaces respectively. Neglect the thermal resistance of the metal surface.
12) A fin 30 cm long and 10 mm diameters throughout is made of steel alloy of thermal
conductivity 43 W/m ??C. The fin attached to a plane heated wall at 200?C, extends into
surroundings at 25?C and unit surface conductance of 120 W/m2 ? ?C. Workout the heat
flow rate from the fin to the surroundings. Presume that the tip of the fin is insulated and
thermal radiation effects are negligible.
13) What is the radiant energy flux from a steel product at 1000 K. The product may be
treated as grey body with constant emissivlty = 0.7. Also workout the wave length
corresponding to the maximum spectral intensity of radiation.
14) For a certain forced convection process, the following correlation applies:
Nu = 0.031(Re)0.75(Pr)0.30
Workout the percentage change in the rate of heat flow per degree temperature difference
when the original coolant is replaced by another fluid having viscosity equal to two third
that of the original coolant. Assume that other fluid variables and configuration remains
the same.
15) Explain the phenomenon of nucleate boiling. List the factors that affect nucleate boiling.
SECTION-C
16) Water enters a counter flow double pipe heat exchanger at 12?C temperature and flow
rate of 0.16 kg/s. The water is to cool alcohol (cp = 2520 kj/kg ? K) from 75?C to 35?C.
The convection coefficient between alcohol and the tube wall is 340 W/m2 ? K and that
between the tube wall and water is 225 W/m2 ? K. Presuming tube to be thin, make
calculations for the capacity ratio, the effectiveness and the heat transfer area required.
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17) Explain in detail the mechanism of forced convection. Show by dimensional analysis that
for problems in heat transfer involving forced convection only, the Nusselt number can
be expressed as a function of Prandtl number and the Reynolds number.
18) Write short notes on the following :
a) Heat transfer from piston crown
b) Radiation shields
c) Nusselt theory of condensation.
NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any
page of Answer Sheet will lead to UMC against the Student.
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This post was last modified on 26 June 2021