Other Bachelor Degree-Other Bachelors Degree HEAT AND MASS TRANSFER(Karunya University, Coimbatore-2012)
Saturday, 24 August 2013 10:32anudouglas
Karunya University
(Karunya Institute of Technology and Sciences)
(Declared as Deemed to be University under Sec.3 of the UGC Act, 1956)
Supplementary Examination – June 2012
Subject Title: HEAT AND MASS TRANSFER Time: 3 hours
Subject Code: 09ME204 Maximum Marks: 100
Answer ALL questions
(Use of approved HMT data books and steam tables are permitted)PART – A (10 x 1 = 10 MARKS)
1. Write the units of heat flux and heat transfer coefficient.
2. In practice, the thermal conductivity of most material is ______ dependent.
3. A solid body is said to be in a steady state if its temperature does not vary with ______.
4. What is the use of Heisler charts in transient heat conduction problems?
5. Write the name of the theorem used for dimensional analysis.
6. Distinguish between natural and forced convection.
7. When is NTU method used for heat exchanger design calculations?
8. What are all the non-dimensional numbers used in mass transfer analysis?
9. What is flow or forced convection boiling?
10. Define emissive power.
PART – B (5 x 3 = 15 MARKS)
11. Explain briefly the Fourier’s law of heat conduction.
12. Describe the concept of lumped heat capacity analysis.
13. Explain the concept of thermal boundary layer with a suitable diagram.
14. Define heat exchanger effectiveness and explain its significance.
15. What is the purpose of providing radiation shield between surfaces?
PART – C (5 x 15 = 75 MARKS)
16. Derive three dimensional heat conduction equation in Cartesian coordinates and deduce it to Poisson and Laplace equations.
(OR)
17. A cold storage room has walls made of 220 mm of brick on the outside, 90 mm of plastic foam, and finally 16 mm of wool on the inside. The outside and inside air temperatures are 250 C and – 30 C respectively. If the inside and outside heat transfer coefficients are respectively 30 and 11 W/m2 K, and the thermal conductivities of brick, foam and wool are 1.02, 0.025 and 0.18 W/m K, respectively, Determine : (a) the rate of heat transfer by refrigeration if the total area is 85 m2, and (b) the interface temperatures of layers.
18. a. Explain the physical significance of Biot and Fourier numbers. (5)
b. An aluminum sphere of radius 9 cm initially at a temperature of 3200C is suddenly immersed in a fluid at 200C. The convective heat transfer coefficient is 58 W/m2 K. Estimate (i) the temperature after 300 seconds and (ii) the time required to cool the sphere to 1000 C, using lumped heat capacity method of analysis. (10)
(OR)
[P.T.O]
19. A slab of aluminum 10 cm thick is originally at a temperature of 5000C. It is suddenly immersed in a liquid at 1000C resulting in a heat transfer coefficient of 1200 W /m2 K. Determine the centerline and the surface temperatures two minutes after the immersion. Also calculate the total thermal energy removed per unit area of the slab during this period. The properties of aluminium for the given conditions are a = 8.4 x 10 -5 m2 /sec, k = 215 W/m K, r = 2700 kg/m3, c = 0.9 kJ/kg K. Use Heisler charts.
20. Air flows over a flat plate at a velocity of 3.2 m/sec and ambient conditions are, pressure is 1 atm and temperature is 150 C. The plate is maintained at 950 C. If the length of the plate is 100 cm along the flow of the air and width is 40 cm, find the heat lost from (a) 50 cm length of the plate and (b) whole length of the plate.
(OR)
21. a. Write short notes on classification and applications of fins. (5)
b. Find the convective heat loss from a radiator 0.5 m wide and 1.0 m high maintained at a temperature of 850 C in a room at 250 C. Consider the radiator as a vertical plate. (10)
22. In a counter flow double pipe heat exchanger; water is heated from 280 C to 800C by oil with a specific heat of 1.45 kJ/kg K and mass flow rate of 1.0 kg/sec. The oil is cooled from 2400 C to 1550 C. If the overall heat transfer coefficient is 420 W/m2 K, calculate the following: (a) the rate of heat transfer, (b) the mass flow rate of water and (c) the surface area of the heat exchanger.
(OR)
23. a. Explain the Fick’s law of diffusion. (5)
b. Ammonia and air are in equimolal diffusion in a cylindrical tube of 3 cm diameter and 1.8 m length. The total pressure is one atmosphere, and the temperature is 280 C. One end of the tube is connected to large reservoir of ammonia and the other end of the tube is open to the atmosphere. If the mass diffusivity for the mixture is 0.3 x 10-4 m2/sec, calculate the mass transfer rates of ammonia and air through the tube. (10)
24. a. Describe the various regimes of pool boiling with a suitable sketch. (10)
b. Explain the concept of black and gray bodies. (5)
(OR)
25. a. Write a note on radiation shape factors. (5)
b. Two large parallel plans of emissivities e1 =0.4 (T = 3370C) and e2 =0.8 (T = 5370 C) exchange heat. Find the net heat radiated by them and percentage reduction in heat transfer when a polished aluminum shield (e= 0.06) is placed between them. (10)
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