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Posted Date: 01 Dec 2008 Posted By: Sunil Reddy Member Level: Platinum
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2005 Jawaharlal Nehru Technological University Mechanical Engineering III B.Tech. I Semester Supplementary Examinations, May -2005 THERMAL ENGINEERING-II Question paper
Code No: RR310303 Set No.3
III B.Tech. I Semester Supplementary Examinations, May -2005
THERMAL ENGINEERING-II
(Mechanical Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. (a) A steam turbine is supplied with steam having an enthalpy of 3000 kJ/kg. It
moves out of the turbine with an enthalpy of 2100 kJ/kg. Feed water heating
is done at a pressure of 3.2 bar with steam enthalpy of 2500 kJ/kg. The
condensate with an enthalpy of 125 kJ/kg enters into the feed water heater.
The quantity of bled steam is 11200 kg/hr. Find the power developed by the
turbine. Assume the water leaving the feed water heater is saturated at 3.2
bar and the heater is direct mixing type.
(b) Write down the advantages of high pressure boilers.
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.
3. (a) With the help of neat sketch explain the working of a surface condenser.
(b) Explain the need of an air pump during the working of surface condenser
4. In an impulse turbine the steam issues from the nozzle with speed of 600 m/s and
blade speed is 120 m/s. the velocity is compounded by passing the steam through
a ring of moving blades; through a ring of fixed blades and finally through a ring
of moving blades.
The nozzle angle is 180 ad the blade exit angles and relative velocity coefficients
are:
1st row moving: 20o & 0.8
fixed row : 25o & 0.85
2nd row moving: 30o & 0.9
find the diagram efficiency under these conditions and the power output for steam
flow rate of 5 kg/sec.
5. (a) What do you mean by compounding of steam turbines? Discuss various meth-
ods of compounding steam turbines?
(b) Explain the difference between an impulse turbine and a reaction turbine?
6. In a gas turbine plant, the air at 2830K and 1 bar is compressed to 4 bar with
Isentropic compressions efficiency of 80% . The air is heated in the regenerator
and in the combustion chamber till its temperature is raised to 9730 K and during
the Process pressure falls by 0.1 bar. The air is then expended in the expander
isentropically and passes through the regenerator which has 0.75 effectiveness and
cause a pressure drop of 0.12 bar. Determine thermal efficiency of the plant if the
isentropic efficiency of expander is 0.85
7. (a) Differentiate between a jet propulsion unit and a gas turbine unit.
(b) Define and derive an expression for the thermal efficiency of turbojet engine.
8. (a) Describe nuclear rocket engine with a neat sketch.
(b) What are the other kinds of rocket propulsion? Mention some of them.
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