B.TECH,2014
HEAT TRANSFER
PAPER CODE:BTME-602
PAPER IF:[A-2362]
Time Allowed: 3 Hours
Max, Marks: 60
Section A
Q1.
a) What is the effect of temperature on thermal conductivity of solids, liquids and
gases? Justify your answer.
b) What is meant by critical thickness of insulation?
c) Define Kirchoff`s law.
d) Write down Fourier, Laplace & Poisson equations of heat transfer.
e) Define thermal diffusivity. What is its physical significance?
f) Define Shape factor.
g) What is critical Reynolds number? State its approximate values for flow over flat
plate and a circulat tube.
h) Define effectiveness and NTU of a heat exchanger.
i) Define hydrodynamic boundary layer. Which non dimentional number governs
the relative magnitude of hydrodynamic and thermal boundary layers?
j) State Buckingham pi theorem. What are repeating variables, how they are
selected?
Section B
[Marks: 5 each]
Q2. Explain different types of condensation.
Q3. Derive three dimensional heat conduction equation in cylindrical coordinates.
Reduce the equation to one dimentional, steady state without internal heat generation.
Q4. Define emissive power and intensity of radiation. Using the concept of solid angle
find relation between the two.
Q5. Prove by dimentional analysis for natural convection, Nu= Φ (Gr, Pr).
Q6. What is the criterion for selection of heat exchangers?
Section C
[Marks: 10 each]
Q7. Derive relation of temperature distribution and heat transfer for thin fin insulated at
the tip.
Q8. Air at 200C and at atmospheric pressure flows at a velocity of 5.5 m/s past a flat
plate with a sharp leading edge. The entire plate surface is maintained at a temperature
of 700C. Assuming that the transition occurs at a critical Reynolds No. of 5x10 5, find the
distance from the leading edge at which the boundary layer changes from laminar to
turbulent. At the location, calculate the following:
i.
ii.
iii.
iv.
Thickness of hydrodynamic boundary layer.
Thickness of thermal boundary layer.
Local & average convective heat transfer coefficients.
Heat transfer rate from both sides per unit width of plate.
Q9. Three hollow thin walled cylinders having diameters 10cm, 20cm, 30 cm are
arranged concentrically. The temperatures of the innermost & outermost cylindrical
surfaces are 150K & 350K respectively. Assuming vacuum between annular spaces,
find the steady state temperature attained by the cylindrical surface having diameter of
20cm. Take ε1= ε2= ε3=0.04.
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