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Reg No.: Name:
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY

Sixth semester B.Tech examinations (S), September 2020

Course Code: ME302
Course Name: Heat and Mass Transfer

Use of heat and mass transfer data book permitted

Max. Marks: 100 Duration: 3 Hours
PARTA
Answer any three full questions, each carries 10 marks. Marks

1 ஐ Derive the expression for critical thickness of a cylinder. What isthe importance (4)
of critical thickness of insulation?

b) A hollow sphere of inner radius 30 mm and outside radius 50 mm is electrically (6)
heated at its inner surface at a constant rate of 10° W/m*. The outer surface is
exposed to a fluid at 30 °C with h = 170 W/m’K. Thermal conductivity of the
material is 20 W/m K. Calculate the inner and outer surface temperatures.

2 a) Air at velocity of 3m/s and at 20°C flows over a flat plate along the length. The (5)
length, width and thickness of the plate are 100cm, 50cm, 2cm respectively. The
top surface of the plate is maintained at 100°C. Calculate the heat lost by the
plate and temperature at bottom surface of the plate for steady state conditions.
Thermal conductivity of plate material is 23 W/mK

b) A vertical plate 15cm high and 10cm wide is maintained at 140°C. Calculate the (5)
maximum heat dissipation rate from both sides of the plate in ambient air at 20°C
by free convection

3 a) Derive the general heat conduction equation in Cartesian coordinates, state the (8)
assumptions.

b) Good electrical conductors usually have the property of high thermal (2)
conductivity. Why?

4 a) Using Buckingham pi theorem derive the expression for flow through a tube (7)
under forced convection . Make suitable assumptions

b) Explain the importance of hydrodynamic and thermal boundary layers in heat (3)

transfer.

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