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Posted By: Sra1 Member Level: Gold Posted Date: 27 May 2008
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2007 Jawaharlal Nehru Technological University B.Tech Aeronautical THERMODYNAMICS (Supplimentary Examinations, Aug/Sep 2007) Question paper
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Set No 4
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Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1. A fluid contained in a horizontal cylinder fitted with a frictionless leak proof piston, is continuously agitated by means of a stirrer passing through the cylinder cover. The cylinder diameter is 0.4 m. During the stirring process lasting 10 minutes, the piston slowly moves out a distance of 0.485 m against the atmosphere. The net work done by the fluid during the process is 2 kJ. The speed of the electric motor driving the stirrer is 840 rpm. Determine torque in the shaft and power output of the motor. [16]
2. A turbo compressor delivers 2.33 m3/s of air at 0.276 MPa, 430C which is heated at
this pressure to 4300C and finally expanded in a turbine which delivers 1860 KW.
During the expansion, there is a heat transfer of 0.09 MJ/sec to the surroundings.
Calculate the turbine exhaust temperature if changes in kinetic and potential energy
are negligible. Take Cp = 1.005 KJ/kg-k and R = 0.287 KJ/Kg-K for air. [16]
3. (a) There exists a property of a closed system such that a change in its value is
equal to dQ/T for any process undergone by the system. Prove this statement.
(b) 5 Kg of water at 300C is mixed with 1 kg of ice at 00C. The process of mixing
is adiabatic. Calculate the temperature of mixture and the change of entropy
for the mixing process. Take specific heat of water = 4.187 KJ/Kg-K and
latent heat of ice = 335 KJ/Kg. [8+8]
4. (a) Steam initially at a pressure of 10.5 bar 0.96 dry throttled to a pressure of 1
bar. Find the final condition of steam. Also calculate the change of entropy
per kg of steam. Assume Cp for super heated steam = 2.1 KJ/kg. k
(b) Find the entropy of 1 kg of super heated steam at a pressure of 12 bar and a
Temperature of 2500C. Take specific of super heated steam as 2.1 kJ/ kg. k
[8+8]
5. (a) Derive an expression for heat transfer in a non-flow constant volume process.
(b) A spherical shaped of 14 M diameter contain ’H2’ at 330C and 1.3 bar. Find
the mass of ’H2’ in the balloon using real gas equation. [7+9]
6. A 2.2 kg mole of Carbon dioxide at a presser of 2 bar, 800C is mixed in a thermally
insulated vessel with 3.2 kg-mol of Nitrogen is at equilibrium; Determine the final
temperature and pressure and the change in entropy of the mixture. [16]
7. In a gas turbine plant working on Brayton cycle, the air at inlet is 27C,0.1 MPa. The pressure ratio is 6.25 and the maximum temperature is 800C. The turbine and compressor efficiencies are each 80%. Find compressor work, turbine work, heat supplied, cycle efficiency and turbine exhaust temperature. Mass of air may be considered as 1 kg. Draw T-s diagram. [16]
8. (a) Explain about the re-heating and refrigeration of a steam cycle with help of neat diagrams?
(b) Obtain an expression for Joule’s cycle in terms of pressure ratio. [8+8]
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