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Posted By: satish Member Level: Gold Posted Date: 11 Feb 2008
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2006 Jawaharlal Nehru Technological University Mechanical Engineering THERMAL ENGINEERINGII III B.Tech I Semester Regular Examinations, November 2006 set 3 Question paper
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Code No: RR310303 Set No. 3
THERMAL ENGINEERINGII
(Mechanical Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. (a) A steam turbine operating on the Rankin cycle receives steam from the boiler
at 3.5 MN/m 2 and 3500C and exhaust to the condenser at 10 kN/m 2 .The
condensate is then returned to the boiler by the feed pump. Determine the
following considering pump work also.
i. the energy supplied in the steam generator
ii. the dryness fraction of the steam entering the condenser,
iii. the Rankin efficiency.
(b) What is the difference between economizer and super heater? Why are they
used in a boiler? [12+4]
2. A convergent divergent nozzle is required to pass 1.8 kg of steam per second. At
inlet the steam pressure and actual temperature are 7 bar and 2000C respectively
and the speed is 75 m/s. Expansion is stable throughout to the exit pressure of
1.1bar. There is no loss by friction in the converging section of the section, but
loss by friction between throat and outlet is equivalent to 71 kJ/kg of steam.
Calculate
(a) the required area of throat in mm2,
(b) the required area of outlet in mm2and
(c) the overall efficiency of the nozzle, based on the heat drop between the actual
inlet pressure and temperature and the outlet pressure. [16]
3. (a) What are the main functions of air pump? Discuss the working of Edward air
pump with a neat diagram ?
(b) Discuss the differences between down flow and central flow condensers ?
[10+6]
4. (a) Define and derive an expression for stage efficiency incase of a steam turbine.
(b) In an impulse turbine the nozzles are inclined at 240 to the plane of rotation
of the blades. Steam speed is 1000 m/sec and blade speed is 400 m/sec.
Assuming equiangular blades, determine
i. blade angles,
ii. axial thrust,
iii. force on the blades in the direction of motion,
iv. power developed for a flow rate of 1000 kg/hr. [8+8]
5. (a) What do you mean by compounding of steam turbines? Discuss various
methods of compounding steam turbines?
(b) Explain the difference between an impulse turbine and a reaction turbine?
[10+6]
6. (a) How the gas turbine cycles classified?
(b) A Gas turbine plant works between the temperature limits of 1152 0 K and
288 0 K Isentropic efficiency for compressor and turbines are 0.85 and 0.8
respectively. Determine the optimum pressure ratio for maximum work output
and also for maximum Cycle thermal efficiency. [6+10]
7. A turbojet
engine consumes air at the rate of 60.2 kg/s when flying at a speed of
1000 km/hr. Calculate:
(a) Exit velocity of the jet when the enthalpy for the nozzle is 230 KJ/kg. and
velocity coefficient of the jet is 0.96
(b) Fuel flow rate in kg/s when airfuel
ratio is 70:1
(c) Thrust specific fuel consumption
(d) Thermal efficiency of the plant when the combustion efficiency is 92% and
the calorific value of the fuel is 42000 KJ/kg
(e) Propulsive power
(f) Propulsive efficiency
(g) Overall efficiency. [16]
8. (a) Where is rocket propulsion is used? What are the kinds of rocket propellants?
(b) Describe a liquid propellant rocket engine with a neat sketch. [12+4]
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