university question

1. Reg. No. :
B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2010
Fifth Semester
Chemical Engineering
CH 2304 — HEAT TRANSFER
(Regulation 2008)
Time : Three hours Maximum : 100 Marks
(Steam Table is permitted)
Answer ALL questions
PART A — (10 × 2 = 20 Marks)
1. State three modes of heat transfer.
2. What is thermal conductivity?
3. What is Natural convection? Explain.
4. What is overall and individual heat transfer coefficient? Explain.
5. What is Forced convection?
6. Give the application of conduction heat transfer?
7. What is the range of dimension for baffle distance in heat exchanger?
8. Why LMTD correction factor adopted in heat exchanger?
9. State the difference between thermal radiation and light radiation.
10. What is Economy in evaporator? Explain.
PART B — (5 × 16 = 80 Marks)
11. (a) (i) Discuss the analogy between flow of heat and electricity. (8)
(ii) A wall of a furnace 0.244 m thick is constructed of material having
thermal conductivity 1.30 w/m°K. The wall will be insulated on the
outer side with the material having average thermal conductivity
0.346 w/m°K so that the heat loss from the furnace will be equal to
or less than 1830 w/m2. The inner surface of the wall is at 1588°K,
while the outer surface is at 299°K. Calculate the thickness of
insulation required. (8)
Or
(b) (i) Derive the steady state heat conduction equation in a rectangular
composite wall comprising three layers. (8)
(ii) What is critical thickness of insulation? And derive the related
equation for cylinder. (8)
12. (a) (i) Derive unsteady state heat conduction equation. (8)
(ii) Discuss graphical method of solving two dimensional steady state
heat conduction. (8)
Or
Question Paper Code : 53093

2. 53093
2
(b) (i) Derive the relevant equation for heat transfer in conduction with
any heat source? (8)
(ii) Discuss the analytical method of solving two dimensional steady
state heat conduction. (8)
13. (a) (i) Steam at pressure of 1.2 atm absolute is condensed in a vertical
condenser at the rate of 6100 kg/hr using water at 33°C. The out let
temperature of water is 80°C. Find out heat load, and cooling water
requirement. (8)
(ii) Discuss the heat transfer to molten metal. (8)
Or
(b) Explain
(i) Pool boiling (5)
(ii) Film type condensation (5)
(iii) Drop wise condensation with a diagram. (6)
14. (a) (i) Explain parallel flow and counter flow heat exchanger. (8)
(ii) A reaction mixture having CP = 2.85 KJ/kg °K is flowing at a rate of
7260 kg/hr is to be cooled from 377.6 to 344.3 °K. Cooling water at
288.8 °K is available and the flow rate is 4536 kg/hr. The over-all
Uo = 653 W/m2°K.
(1) For counter flow, calculate the outlet water temperature and
area of heat exchanger
(2) For co-current flow calculate the area of heat exchanger.
(8)
Or
(b) (i) Differentiate single pass exchanger from multi-pass heat
exchanger. (5)
(ii) What is plate type heat exchanger and explain with a diagram. (5)
(iii) What is fouling and how it can be prevented in heat exchanger? (6)
15. (a) (i) Derive the equation for radiation exchange between large grey
concentric cylinders. (10)
(ii) Two parallel gray planes which are having emissivities of
Є1 = 0.8, Є2 = 0.7. The surface is at 866.5 °K and surface 2 is at
588.8 °K.
(1) What net radiation from 1 to 2?
(2) If both surfaces are black, what net radiation from 1 to 2? (6)
Or
(b) (i) A feed of 4535 kg/hr of a 2% by weight salt solution at 311 °K enters
continuously a single effect evaporator and being concentrated to
3% by weight. The evaporation is at atmospheric pressure and the
area of the evaporator is 69.7 m2. Saturated steam at 383.2 °K is
supplied for heating. Since the solution is dilute, it can be assumed
to have same boiling point of water. Cp, of feed is 4.10 KJ/kg °K.
Calculate the overall heat transfer coefficient. (8)
(ii) Explain various types of feeding in multiple effect evaporators.
(8)
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