VASAVI COLLEGE OF ENGINEERING (Autonomous)

IBRAHIMBAGH, HYDERABAD – 500 031

DEPARTMENT OF MECHANICAL ENGINEERING

B.E. VI Semester (Main) Examinations, May-June 2023

Heat Transfer (PE-II)

Time: 3 hours Max. Marks: 60

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Note: Answer all questions from Part-A and any FIVE from Part-B

Part-A (10 x 2 = 20 Marks)

1. Define thermal conductivity and write its units.
2. What is meant by critical thickness of insulation?

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3. Define fin efficiency and fin effectiveness.
4. What is lumped system analysis?
5. What are the advantages of dimensional analysis?
6. What is the physical significance of Nusselt number?
7. Define condensation and boiling.

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8. State Stefan Boltzmann’s law of radiation.
9. What is a radiation shield?
10. Define shape factor.

Part-B (5 x 8 = 40 Marks)

1. a) Derive the general heat conduction equation in Cartesian coordinates.

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   b) A furnace wall is made up of three layers of thicknesses 25 cm, 10 cm and 15 cm with thermal conductivities of 1.65, K and 9.2 W/mK respectively. The inner surface is at 850°C and the outside surface is at 100°C. If the temperature at the interface of the first two layers is 550°C, determine the value of K and the percentage of total heat resistance.

2. a) Derive an expression for temperature distribution and heat dissipation in a straight fin of rectangular profile for the case when the fin is infinitely long.

   b) A steel rod (k = 32 W/mK), 12 mm in diameter and 60 mm long, with an insulated end is to be used as a spine. It is exposed to surroundings with a temperature of 60°C and a heat transfer coefficient of 55 W/m²K. Determine the fin effectiveness and the heat dissipation from the fin.

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3. a) Explain the significance of dimensionless numbers:

   i) Reynolds number ii) Prandtl number iii) Grashoff number iv) Stanton number

   b) A horizontal steam pipe of 50 mm diameter is placed in a room at 20°C. The outside surface temperature of the pipe is 134°C. Determine the heat loss per unit length of the pipe by free convection. Use the correlation: Nu = 0.53(Gr.Pr)^1/4

4. a) Differentiate between forced and free convection.

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   b) Air at 20°C flows over a flat plate at a velocity of 3 m/s. The plate is 2.8 m long and 1.5 m wide. Calculate the following: i) Boundary layer thickness at the trailing edge of the plate ii) Total drag force iii) Total heat transfer from the plate, if the plate is maintained at 60°C.

5. a) Differentiate between Film wise and Drop wise condensation.

   b) A vertical plate 400 mm high and 200 mm wide is to be used to condense saturated steam at atmospheric pressure. If the plate temperature is maintained at 80°C, calculate the condensation rate and the heat transfer rate.

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6. a) State and prove Kirchhoff’s law of radiation.

   b) Two large parallel plates with emissivities 0.5 and 0.8 exchange heat. Find the percentage reduction in heat transfer when a polished aluminum radiation shield of emissivity 0.04 is placed between them.

7. Write short notes on any two of the following:

   a) Fouling factor

   b) Shell and tube heat exchanger

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   c) Transient heat conduction

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