BBA Iind SEMESTER EXAMINATION 2008-09 s22

M.Tech III (Third) Semester Examination 2013-14

Course Code: MME303 Paper ID: 0973203

Heat Exchangers

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) What do you mean by fouling in heat exchanger? b) What causes tube vibration in heat exchanger and why is it detrimental? c) What problem may arise in the condenser if it is not provided with vent? d) What safety measures are required if the shell side pressure is high? e) What factors are responsible for deterioration of performance of heat exchanger? f) What type of problem may occur if shell liquid has suspended solid particles?. g) Mention two symptoms that indicate underdesign of condenser. h) What is the simplest practical solution for heat exchanger having leaking tube?

2. Define effectiveness and NTU of heat exchanger. Discuss the advantage of NTU method of heat exchanger design over LMTD method. (10) 3. A heat exchanger contains 4500 tubes, each having a diameter of 2.54 cm, through which 11.3 kg/s air to be cooled from 538 oC to 148 oC. Water passes in counter flow over the tubes, rising in temperature from 38 oC to 85 oC. Determine the tube length required for this duty, if the waterside resistance to heat flow is negligible. The physical properties of air at average temperature are as under: ρ = 1.009 kg/ m3 μ = 2.075 x 10-5 kg/ms -5 k = 3.003 x 10 kW/m K cp = 1.0082 kJ/kg K For turbulent flow inside tubes, use relation Nu = 0.023 Re0.8 Pr0.3 . (10)

4. A double pipe parallel flow heat exchanger uses oil (cp = 1.8 kJ/kg K) flowing at 0.75 kg/s with an initial temperature of 200 oC to heat water flowing at 0.0625 kg/s from 15.55 oC. Calculate the final temperature of oil and water if U= 205 W/m2K and A = 0.15 m2. (10)

5. Hot oil (cp = 2.09 kJ/kg-K) flows through a counter flow heat exchanger at the rate of 0.63 kg/s. It enters at 193 oC and o o leaves at 65 C. Cold oil ( cp = 1.67 kJ/kg K) exits at 149 C at the rate of 1.0 kg/s. What area is required to handle the load if the overall heat transfer coefficient based on the inside area is 0.7 kW/m2 K. (10)

6. What is meant by fouling factor? How does it affect the performance of a heat exchanger? (10)

7. Explain briefly the design procedure for a shell and tube heat exchanger. (10)

8. Write short notes on any four of the following: (2.5x4=10) a) Shell and tube condensers b) Flow Mal distribution in heat exchanger c) Rating of air cooled heat exchangers d) Pressure drop and pumping cost in heat exchanger e) Organization of input data in design of heat exchanger