Rr221403-thermal-engineering-and-heat-transfer

Set No. 1

Code No: RR221403

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 THERMAL ENGINEERING AND HEAT TRANSFER ( Common to Mechatronics and Production Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Derive an expression for the mean effective pressure of diesel cycle. (b) The ideal Otto engine working on the air standard cycle has a temperature and pressure at the beginning is 250 C and 1 bar respectively and a thermal efficiency of 48%. Determine the pressure and temperature at the end of compression. [8+8] 2. What is the effect of high sulphur content on the performance of S1 and C1 engine? Discuss. [16] 3. (a) What are the various characteristics of an efficient cooling systems? (b) Explain with the help of sketches i. Thermosyphon cooling system: ii. Pressure cooling system.

[6+10]

4. (a) List the types of exhaust temperature measurement. (b) Explain an automatic fuel flow meter.

[4+12]

5. (a) Sketch a line diagram of a semi-closed gas turbine cycle. Indicate its place of operation. (b) Discuss the relative advantages and disadvantages of reciprocating I.C.engines and gas turbines. [8+8] 6. (a) Derive an expression for the overall coefficient of heat transfer based on the inside area for the composite cylinder having two layers with fluid boundaries. (b) A brick wall 25 cm thick is faced with concrete of 5 cm thick. The thermal conductivity of the brick is 0.7 W/mK while that of the concrete is 0.9 W/mK. If the temperature of the exposed brick face is 300 C and that of the concrete is 50 C, find the heat loss per hour through a wall of 10 × 5m. [8+8] 7. The parallel outer and inner walls of a building are 4m high and 5m long. The walls are 10 cm apart. The inner surface of the inner wall is at 250 C and the inner surface of the outer wall is at 50 C. (a) Calculate the total heat loss per hour. (b) If the air space is divided in half by a sheet of aluminium foil 0.025 mm thick parallel to the walls, what would be the heat loss per hour. [16] 8. (a) When a body is said to be black? What is the range of wave lengths it absorbs? 1 of 2

Set No. 1

Code No: RR221403

(b) Compute the radiant energy loss from 1 cm diameter opening in a thin walled furnace located in a large enclosure, if the temperature with in the furnace is 9000 C and the surroundings are at 200 C. [6+10] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: RR221403

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 THERMAL ENGINEERING AND HEAT TRANSFER ( Common to Mechatronics and Production Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Derive an expression for the mean effective pressure of diesel cycle. (b) The ideal Otto engine working on the air standard cycle has a temperature and pressure at the beginning is 250 C and 1 bar respectively and a thermal efficiency of 48%. Determine the pressure and temperature at the end of compression. [8+8] 2. (a) Describe the important qualities of a CI engine fuel. (b) Briefly describe the rating of CI engine fuel.

[8+8]

3. (a) Why is over-cooling in an engine harmful? (b) What are the two main types of cooling systems? Where these system are used? (c) Describe Miller super charging.

[4+4+8]

4. (a) Define mean effective pressure and distinguish between brake mean effective pressure and indicated mean effective pressure. (b) How smoke density can be measured? Describe with sketch the principle of Bosch or Hartridge smoke meter. [6+10] 5. (a) What are the desirable properties of fluid suitable for closed cycle operation? Also explain the disadvantages of a closed cycle gas turbine over open cycle gas turbine. (b) Air enters the compressor of an open cycle constant pressure gas turbine at 1 bar and 300 C. The pressure of air after the compression is 4 bar. The isoentropic efficiencies of compressor and turbine are 75% and 80% respectively. The air fuel ratio used is 75%. Find the I.P and thermal efficiency of the cycle if the flow rate of the air is 2.5kg/sec. Take Cp =1 kJ/kg and γ=1.4 for air and gases. C.V of fuel used is 42000 kJ/kg. [8+8] 6. (a) What is the basic difference between conduction and radiation heat transfer processes? (b) Identify the modes of heat transfer in the following examples. i. ii. iii. iv.

A car disc brake during braking A domestic boiler Heating a room using an electric fan heater Soldering an electric circuit board 1 of 2

Set No. 2

Code No: RR221403 v. Gas welding two sheets of steel plate.

[6+10]

7. (a) Define Nusselt and Prandtl numbers. Explain their importance in convection heat transfer. (b) A vertical pipe 5 cm diameter carrying hot water is exposed to ambient air at 150 C. If the outer surface of the pipe is 650 C, find the heat loss from one metre height of the pipe per hour. [8+8] 8. (a) When a body is said to be black? What is the range of wave lengths it absorbs? (b) Compute the radiant energy loss from 1 cm diameter opening in a thin walled furnace located in a large enclosure, if the temperature with in the furnace is 9000 C and the surroundings are at 200 C. [6+10] ⋆⋆⋆⋆⋆

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Set No. 3

Code No: RR221403

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 THERMAL ENGINEERING AND HEAT TRANSFER ( Common to Mechatronics and Production Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define i. bore and stroke ii. displacement and clearance volume. (b) Discuss the merits and demerits of 2 stroke engines over 4 stroke engines.[8+8] 2. Explain why a rich minute is required for the following: (a) Idling (b) Maximum power (c) Sudden acceleration

[5+5+6]

3. (a) What are the limits of turbo charging? (b) What are the various components to be lubricated in an engine and explain how it is accomplished? [4+12] 4. (a) List the parameters by which performance of an engine is evaluated. (b) What are the various methods for measurement of brake house power?[6+10] 5. An open cycle gas turbine plant consists of compressor, combustion chamber and turbine. The pressure and temperature at the inlet of compressor are 1 bar and 150 C and at the inlet of the turbine are 5 bar and 6500 C. Assume ζe = 80%, ζt = 85%, ζm = 90% and ζcom =98%. Assuming Cpa = 1 KJ/kg K, Cpg = 1.2 kJ/kg K and ν (for air) = 1.4 and r(for gases) = 1.334. Find (a) the thermal efficiency (b) work ratio of the cycle. If a regenerator of 65% effectiveness in introduced in the cycle, with a pressure loss of 0.2 bar to air side as well as gas side, find the percentage increase in the thermal efficiency of the cycle. [16] 6. (a) What are different modes of heat transfer? Discuss the mechanism of conduction heat transfer in solids. (b) Identify the various modes of heat transfer in the following cases. i. Heat transfer from an auto radiator ii. Condensation of steam in condenser iii. Heat loss from a thermos flask 1 of 2

Set No. 3

Code No: RR221403

iv. Protection of human body with warm clothing in winter.

[8+8]

7. (a) Explain the difference between natural and forced convection. (b) State the Buckingham’s Π-theorem. Using dimensional analysis obtain an expression for Nusselt number in terms of Reynolds and Prandtl numbers. [4+12] 8. (a) What is the geometrical factor of radiation? Explain. (b) Estimate the heat loss by radiation from a high pressure steam pipe at a temperature of 1270 C situated in a large room whose walls are at 270C. Assume emissivity of pipe surface to be 0.8. [8+8] ⋆⋆⋆⋆⋆

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Set No. 4

Code No: RR221403

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 THERMAL ENGINEERING AND HEAT TRANSFER ( Common to Mechatronics and Production Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) What do you mean by air standard cycles? What are the assumptions for air standard cycles? (b) Derive an equation for the air standard efficiency of an engine working on the Otto cycle in terms of its compression ratio and ratio of specific heats of air. [6+10] 2. What are the different kinds of fuels used in an IC engine? Discuss them in detail. [16] 3. (a) What is the purpose of the fan radiator system? Is it required at all times? Why? (b) What is the effect of super charging on the following parameters: i. Power output ii. Mechanical efficiency iii. Fuel consumption

[4+12]

4. (a) Explain the functions of a nozzle. (b) Explain the working of a fuel injector with the help of a neat sketch. [4+12] 5. (a) Sketch a line diagram of a semi-closed gas turbine cycle. Indicate its place of operation. (b) Discuss the relative advantages and disadvantages of reciprocating I.C.engines and gas turbines. [8+8] 6. Prove that the heat loss per square metre of outside surface area of a hollow sphere heated from within is equal to q =

2k(T1 − T2 ) D2 (D2 − D1 ) D 1

where T1 and T2 are the temperatures and D1 and D2 are the diameters of the inner and outer surfaces respectively. [16] 7. The parallel outer and inner walls of a building are 4m high and 5m long. The walls are 10 cm apart. The inner surface of the inner wall is at 250 C and the inner surface of the outer wall is at 50 C. (a) Calculate the total heat loss per hour. 1 of 2

Set No. 4

Code No: RR221403

(b) If the air space is divided in half by a sheet of aluminium foil 0.025 mm thick parallel to the walls, what would be the heat loss per hour. [16] 8. (a) What do you mean by ‘total emissive power’ ? State Stefan-Boltzman Law and explain. (b) The concentric spheres, 20 cm and 30 cm in diameter are used to store liquid oxygen at -1530 C in a room at 3000 K. The space between spheres is evacuated. The surfaces of the spheres are highly polished as E = 0.04. Find the rate of evaporation of liquid oxygen per hour. Take latent heat of oxygen as 209 kJ/kg. [6+10] ⋆⋆⋆⋆⋆

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