Con. 3271-11. 7RK-1185

[Total Marks : 100(3 Hours)

N .S. • .Questton No !i compulsory.• Answer any 'four out oC remaining six questions.• Assu~ptions made should be clearly stated.• Assume suitable data wherever required, but justify the same.• Use of ~ Table,GasTable and Mollier Chart permitted.

\1, (a) Prove that internal energy is a property of the system.

(b) Explain how heat pump is more efficient for heating application than electricalheating.

'O'rDetermine the maximum work obtainable from a Heat Engine exchanging heatwith two finite bodies of equal heat capacities at temperatures T\ and T2 (T 1 > T2)

(c) Explain with examples the limitations of First Law of'Therrmodynamics. (5)Or

Discuss the differences between Carnot and Rankine Cycle(d) What is cut off ratio. Discuss its effect on the thermal efficiency of Diesel Engine. (5)

OrDerive an expression for decrease in availability due to heat transfer with finitetemperature difference.

(5)(5)

2.(a) State and explain the equivalence of Kelvin Planck and Clausius statements of (6)Second Law of Thermodynarncs.

(b) Define C.O.P of Heat Pump and Refrigerator and derive the relationship between (4)the two. '

(c) A turbocompressor delivers 2.33 1113 Is of air at 0.276 MPa, 430 C which is (10). heated at this pressure to 430 0 C and finally expanded in a turbine which delivers860 kW.During expansion there is a heat transfer of 0.09 MJ/s to the surroundings.Calculate the turbine exhaust temperature if changes in kinetic and potential energyare negligible.

3.(a) A heat engine operating between two reservoirs at 1000 K and 300 K is used to (10)drive a heat pump which extracts heat from the reservoir at 300 Kat a rate twicethat at which the engine rejects heat to it. lfthe efficiency of the engine is 40%of the maximum possible and the COP of the heat pump is 50% of themaximum possible what is the temperature of the reservoir to which the heatpump rejects heat? What is the rate of heat rejection from the heat pump ifthe rateof heat supply to the engine is 50 kW .

(b) Derive expression for work done in a reversible polytropic process executed by (4)a closed system. .

(c) Explain in brief Joule Thompson Porous Plug Experiment. Draw an inversion curve (6)and explain the significance of Joule Thompson Coefficient.

4.(a) State the principle of increase of entropy of the universe and discuss anyone (4)application.

(b) 0.5 kg of air initially at 25 0 C is heated reversibly at constant.pressure till.the (8)volume is doubled and is then heated reversibly at constant volume till the pressure'is doubled. For the total path find the change in entropy.

(c) In an air standard cycle pressure at the beginning of compression is 1 bar, while (8)temperature is 310 K. Compression ratio is 10:1. Heat added is 2800 kJ/kg of charge.The maximum pressure limit is 70 bar. If heat is added partially at constant volumeand partially at constant pressure find (i) Air standard efficiency Ii) Mean effectivepressure.

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Con. 3271-RK-1185-11. 2

5.(a) Two kg of air at 500 kPa , 80° C expands adiabatically in a closed system until its (10)volume is doubled and its temperature becomes equal to that ofthe surroundingswhich is at 100 kPa ,5° C . for this process determine (i) the maximum work(ii) the available energy (iii) the irreversibility.

(b) A cyclic steam power plant is to be designed for steam temperature at inlet of (10)3600 C and an exhaust pressure of 0.08 bar. After isentropic expansion of steamin the turbine, the moisture content at the 'turbine exhaust is not to exceed 15%.

Determine the greatest allowable steam pressure at the turbine inlet and calculatethe Rankine cycle efficiency for these steam conditions. Estimate also the meantemperature of heat addition.

dA/A = dV/V * (l - M2).Explain the significance of the above relationship,

6,(a) Define Dryness fraction, Critical Point, Triple Point and Degree of Superheat (4)(b) Water at 40 0 C is continuously sprayed into a pipeline carrying 5 tons of steam (6)

per hour at 5 bar, 300 0 C .At a section downstream where the pressure is 3 bar,the. quality is to be 95 %. Find the rate of water spray in kg/hr.

(c) A gas initially at 14.4 bar and 360°C is expanded isothermally to a (10)pressure of2.24 bar.It is-then cooled at constant volume till the pressure falls to1.02 bar.Finally an adiabatic compression brings the gas back to the initialstate. The mass of the gas is 0.23 kg and Cp= 1 KJ/kg K. Draw the p-v diagramand determine:

i) The value of theadiabatic index. of compression, .Li)The change in internal energy of the gas during the adiabatic process.

7. (a) Derive with usual notations the relation for one dimensional isentropic flow (8)of gas,

(b) A conical air diffuser has an intake area of 0.11 m2 and an exit area of 0.44 m2. (8)Air enters the diffuser with a static pressure of 0.18 MPa, static temperature of

370 C and velocity of267 m/s. Calculate (i) The mass flow rate of air through

the diffuser

(ii) The Mach Number, static temperature arid static pressure of air leaving the diffuser

and (iii) the net thrust acting upon the diffuser assuming that its outer surfaces are

wetted by atmospheric pressure at 0.1 MPa :

(c) Derive an expression for optimum pressure ratio in a Brayton Cycle in terms of (4)maximum and minimum cycle temperatures.

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