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Posted By: Sra1 Member Level: Diamond 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
Set No 3
---------------
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1. (a) Write the differences between system and control volume.
(b) A gas undergoes a reversible non-flow process according to the relation P =
(-3V+15)where V is the volume in m3 and P is the pressure in bar. Determine
the work done when the volume changes from 3 to 6 m3. [6+10]
2. (a) A domestic refrigerator is loaded with food and the door closed. During a
certain period the machine consumes 1 KW-hour of energy and the internal
energy of the system drops by 5000 KJ. Find the net heat transfer for the
system.
(b) 1.5 kg of liquid having a constant specific heat of 2.5 KJ/kg-k is stirred in
a well insulated chamber causing the temperature to rise by 150C. Find E
and W for the process. [8+8]
3. In a steam boiler, hot gases from a fire transfer heat to water which vaporizes
at constant temperature. In a certain case, the gases are cooled from 11000C to
5500C while the water evaporates at 2200C. The specific heat of gases is 1.005
KJ/Kg-K, and the latent heat of water at 2200C, is 1858.5 KJ/Kg. All the heat
transferred from the gases goes to the water. How much does the total entropy
of the combined system of gas and water increase as a result of the irreversible
heat transfer? Obtain the result on the basis of 1 kg of water evaporated. If the
temperature of the surroundings is 300C, find the increase in unavailable energy
due to irreversible heat transfer. [16]
4. (a) Explain the following terms related to steam.
i. External work of evaporation
ii. Entropy of evaporation
(b) The following observations wave taken with a separating and throttling col-
orimeter arranged in series. Water separated = 2kg , steam discharged from
the throttling colorimeter =20.5kg ,temperature of steam after throttling =
1100C , initial pressure = 12 bar( absolute), barometer =760 mm of Hg, final
pressure =5mm of Hg. Estimate the quality of steam supplied. [6+10]
5. (a) Express the Vander waal’s constant in terms of critical properties.
(b) Atmospheric air is sucked in an internal combustion engine cylinder. The pres-
sure, temperature and volume of air after suction are 1bar, 750Cand800cm3
respectively. The air is then reversibly compressed to 15bar and 1/8th of its
volume. Heat of combustion of fuel is then added to air at constant volume
until its pressure is 50bar
i. Determine the index of compression process
ii. Calculate the change in entropy of air during each process.
iii. Determine if there is any heat exchange between air and cylinder walls
during compression. state the direction of heat flow. [7+9]
6. A 1.8 kg mole of Carbon dioxide at a presser of 1.8 bar, 750C is mixed in a thermally
insulated vessel with 2.8 kg-mol of Nitrogen is at equilibrium; Determine the final
temperature and pressure and the change in entropy of the mixture. [16]
7. (a) Discuss the use of air standard cycle analysis for the study of internal com-
bustion engines.
(b) An engine of 250 mm bore and 375 mm stroke works on Otto cycle. The
clearance volume is 0.00263m3. The initial pressure is limited to 25 bar, find
the following:
i. The air standard efficiency of the cycle.
ii. The mean effective pressure for the cycle. [6+10]
8. (a) State the merits & demerits of regenerative cycle and reheat Rankine cycle.
(b) Find the C.O.P of a refrigeration system if the work input is 75kJ/kg and
refrigeration effect produced id 160kJ/kg [10+6]
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