B.Tech V (Fifth) Semester Examination 2012-13

Course Code: EME505 Paper ID: 0965220

Heat and Mass Transfer

Time: 3 Hours Max. Marks: 70 Max Marks: 75

Note: Attempt six questions in all. Q. No. 1 is compulsory.

1. Answer any five of the following (limit your answer in 50 words). (4x5=20)

a) How is thermal conductivity of a material defined? What are its units?

b) Differentiate between pool boiling and forced convection boiling.

c) Explain the term thermal capacity and thermal diffusivity of a material.

d) What are the assumptions for lumped capacity analysis?

e) Define the momentum thickness and displacement thickness.

f) Discuss various rules used in determination of radiation shape factor.

g) Discuss Flick’s law of diffusion.

h) What is the effectiveness of fin?

2. a) Define thermal conductivity. How do thermal conductivities of gases and liquids vary with temperature? (5)

b) What do you under stand by combined heat transfer mechanism? Explain. (5)

3. A very long fin is exposed to air at 400°C. The temperature at location 25 mm and 120 mm from the base of fin are 325°C and 375°C respectively. Find the box temperature of fin. (10)

4. Differentiate between: (5+5)

a) Reynold’s number and Grashoff’s number.

b) Hydrodynamic and thermal boundary layer thickness

5. Two large plates maintained at 800°C and 300°C have emissivities as 0.3 and 0.5 respectively. Find the net radiant heat exchange per square meter for these plates. Value of Stefan-Boltzmann constant is 5.669x10-8 W/m2k4. (10)

6. The flow rates of hot and cold water steams running through a parallel flow heat exchanger are 0.2 kg/s and 0.5 kg/s respectively. The inlet temperatures on the hot and cold sides are 70°C and 15°C respectively. The exit temperature of hot water is 40°C. If the individual heat transfer coefficients on both sides are 630 W/m20C, calculate the area of the heat exchanger. (10)

7. Derive expression for effectiveness of parallel flow heat exchanger in terms of NTU. (10)

8. Calculate the rate of heat transfer per unit area through a copper plate 45 mm thick, whose one face is maintained at 350°C and the other face at 50°C. Take thermal conductivity of copper as 370 W/m°C. (10)