8/12/2019 ME132 Thermodynamics Nov Dec 2007

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Reg. No. :

q%e4B.E./8.TECh.DEGREE EXAMINATION, NOVEMBER/DECEMBER 2OO.

SecondSemesterMechanical Engineering

ME 132_ THERMODYNAMICSfime : Three hours Maximum: 100marks

Answer ALL questions.PARTA- (10 x2=20 marks)

1. State the first law for a closedsystem undergoing a changeofstate.

2. What are point functions and path functions and give examples for each.

3. What are the limitations of the first law of thermodynamics?

4. State the Kelvin - Planck and Clausius statements.

5. What are reduced properties? Give their signifrcance.

6. Define Joule - Thomson coefficient.

7. Define wetness fraction of steam.

8. Define dew point temPerature.

9. Why excessair is supplied in the combustionof solid fuels?' L0. Indicate the methods to analyze the flue gas composition?

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PARTB- (5x16=80marks )11. (a) A piston and cylinder machine contains a fluid system which passes

through a completecycle of four processes.During a cycle, he sum of ailhe'at transfers is -170 kJ. The system completes 100 cycles per min.Complete the following table showing the method for each item, andcompute he net rate of work output in kW.

Process Q (kJ/min) W (kJ/min) AE (kJ/min)a -b 0b - c 21000c - d -2100

21700

-36000d - a

Or(b) Air flows steadily at the rate of 0.5 kgls through an air compressor,

entering at7 lrr,Jselocity. 100 kPa pressule, and 0.95 m3/hgvolume andleaving at 5 m/s, 700 kPa and 0.19 m3/hg.The internal energy of the airIeaving is 90 kJ/kg greater than that of the air entering. Coolingwater inthe compressorackets absorbsheat from the air at the rate of 58 kW.

Compute the rate of shaft work input to the air in kW

Find the ratio of the inlet pipe diameter to outlet pipe diameter.72. (a) A closed system consists of 1 kg of air which is initially at 1.5 bar

and 67'C. The volume doubles as the system undergoes a processaccording to the law PV12= C . Find the work done, heat transfer andthe change n entropy during this process.For air R = 0.287/kJ/kg k andT = L'4 '

Or(b) A gas is flowing through a pipe at the rate of 2 kgls' Because ofinadequate insulation the gas temperature decreases rom 800 to 790 C

between two sections n the pipe. Neglecting pressure losses,calculatethe irreversibility rate (or rate of energ:ydegradation) due to this heatloss. Take To = 300 K and a constant Cp = 1.1kJnrgK. For the sametemperature drop of 10'C when the gas cools rom 80'C to 70'C due toheat loss, what is the rate of energy degradation?Take the same valuesof To and C,. What is the inferenceyou can draw from this example?

(i)(ii)

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13. (a) Calculate he pressureof steamat a temperatureof 500'C and a densityof 24kg/m3using(i) the ideal - gas equation(ii) the Van der Waalsequation(iii) the Redlich - Kwong equation(iv) the compressibility factor, and(v) the steam able.

Or(b) Prove hat Co - C, = -T (aV/aT)i GP/AV)r. 'vVhatare the factsonecan

infer from the aboveequation?L4. (a) (i) Explain with a neat sketch the construction of the Mollier diagramand give its use n thermodynamic process epresentation. (g)

(ii) Determine the volume change when I kg of saturated water iscompletely vaporized at a pressure of (1) 1 kpa (2) 100 kpa and(3) 10,000 Pa. (8)Or

(b) Atmospheric air at 1.0132bar has a DBT of B2 c and a wBT of 26 C.Compute(i) the partial pressureof water vapour(ii) the specifichumidity(iii) the dew point temperature(iv) the relative humidity(v) the degreeofsaturation(vi) the densiiy of the air in the mixture(vii) the density of tire vapour in the mixtnre and(viii) the enthalpy of the mixture.

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15. (a) (i ) Hexane (CoHr,) is burnt wlth 80Voheoretical air. The incomplete,combustion produces co2, co, Hro and N, in products. calculatethe air fuel ratio by mass and also the mass fraction of theconstituents of the dry combustionproducts- (10)

(ii) Briefly explain the properties of solid, liquid and gaseous ue}.Or

(b) Briefly explain how the adiabatic flame temperature for a given fuel - airmixture gets affectedwith equivalenceratio'

(6)

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