Mechanical Engineering (Semester 3)
TOTAL MARKS: 80
TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks.
Answer any Five of the following:
1 (a) State the first law of thermodynamics for the Closed system undergoing a cycle.(4 marks)
1 (b) Explain Zeroth Law of Thermodynamics.(4 marks)
1 (c) Show that entropy is property of system.(4 marks)
1 (d) Define Availability and Unavailability.(4 marks)
1 (e) Define COP for refrigerator and heat pump. Derive relation between them.(4 marks)
1 (f) Define:
i) Dryness Fraction
ii) Sensible heat of water
iii) Latent heat of vaporisation
iv) Superheated Steam.(4 marks)
2 (a) State the Kelvin Planck and Clausius statement and establish the equivalence of both for Second law of Thermodynamics.(8 marks)
2 (b) One kg of dry saturated steam undergoes an isentropic expansion process from 10 bar to
i) In a cylinder fitted with a piston
In a turbine.(12 marks)
3 (a) State and derive Steady flow energy equation and apply it to a boiler, condenser, nozzle and turbine.(8 marks)
3 (b) Liquid Octane C8 H18 at 25°C is used as fuel. Air used is 150% of theoretical air and is supplied at 25°C. Assume a complete combustion and the product leaves the combustion chamber at 1600K. Calculate heat transfer per kg mole of fuel. Use the following data
|
Substance |
h°f (MJ/Kmole) |
h298K (MJ/Kmole) |
h1600K (MJ/Kmole) |
|
C8H18 |
-250 |
- |
- |
|
O2 |
- |
8.68 |
52.96 |
|
N2 |
- |
8.67 |
50.57 |
|
H2O (gas) |
-241.8 |
9.9 |
62.75 |
|
CO2 |
-393.5 |
9.36 |
76.95 |
(12 marks)
4 (a) Derive an expression for efficiency of Diesel cycle.(8 marks)
4 (b) A mass of air initially at 206°C is at a pressure of 7bar and has a volume of 0.03m3. The air is expanded at constant pressure to 0.09m3, a polytrophic process with n=1.5 is then carried out, followed by a constant temperature process which completes the cycle. All the processes are reversible. Sketch the cycle on pressure-volume diagram and find the heat received and heat rejected in the cycle.
Take R=0.287 KJ/KgK, Cv=0.713 KJ/KgK.(12 marks)
5 (a) Explain Maxwell relations.(4 marks)
5 (b) Explain Clausius-Clapyeron Equation.(4 marks)
5 (c) An engine working on the Otto Cycle is supplied with air at 0.1 MPa and 35°C. The compression ratio is 8. Heat supplied is 2100 KJ/kg. Calculate the maximum pressure and temperature of the cycle, the cycle efficiency and mean effective pressure.(12 marks)
6 (a) Explain
i) Combustion
ii) Enthalpy of Formation
iii) Enthalpy of Combustion
iv) Adiabatic flame temperature(8 marks)
6 (b) A reversible engine receives heat from two thermal reservoir maintained at constant temperature of 750K and 500K. The engine develops 100KW and rejects 3600 KJ/min of heat to a heat sink at 250K. Determine the heat supplied by each thermal reservoir and thermal efficiency of the engine.(12 marks)
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