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03000ME302052002

PART B
Answer any three full questions, each carries 10 marks.
What is lumped system analysis? Derive an expression for temperature
distribution in a lumped system in terms of initial temperature and ambient
temperature.
A metallic sphere of 25 mm diameter (k = 40 W/m°C, p = 7900 kg/m’, c = 480
J/kg°C) is cooled by exposing air at 25°C with a convective heat transfer
coefficient of 125 W/m? °C. Find the time required to cool the sphere from 650°C
to 150°C.
Derive the governing differential equation for a rectangular fin of constant area of
cross-section. Find the expression for temperature distribution for an infinitely
long case.
Mention the important classifications in heat exchangers with examples for each
one.
With the aid of a temperature distribution curve, derive the expression for the
logarithmic mean temperature difference of a parallel flow heat exchanger.
In a shell and tube type counter flow heat exchanger, water flows through a copper
tube 20 mm LD. and 22 mm O.D., while oil flows through the shell. Water enters
at 20°C and comes out at 30°C, while oil enters at 80°C and comes out at 60°C.
The water and oil side film coefficients are 4400 and 1250 W/m?°C respectively.
The thermal conductivity of the tube wall is 350W/m°C. If the length of the tube
is 2.5 m, calculate the overall heat transfer coefficient and the heat transfer rate.
PART C
Answer any four full questions, each carries 10 marks.
What is a black body? What are its properties?
Explain Planck’s Law and Wein’s displacement law of radiation.
Define shape factor. What is reciprocity theorem?
The radiation shape factor of one circular surface of a thin hollow cylinder, 10 cm
diameter and 10 cm long, to the other circular surface is 0.2. What is the shape
factor of the curved surface of the cylinder with respect to itself?
Two large parallel plates are kept at 500°C and 30°C. Calculate the net radiation

exchange per unit area between the plates. The emissivities of the plates are 0.8

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