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Posted Date: 08 Feb 2009 Posted By: ram Member Level: Diamond
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2008 Jawaharlal Nehru Technological University Mechanical Engineering Code No: R05 III B.Tech I Semester Regular Examinations, November 2008 THERMAL ENGINEERING-II Question paper
Code No: R05310306 Set No. 4
III B.Tech I Semester Regular Examinations, November 2008
THERMAL ENGINEERING-II
( Common to Mechanical Engineering and Automobile Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. (a) Draw the T-S and H-S diagrams of reheat cycle representing all the salient
points.
(b) In a steam power plant the condition of steam at inlet to the turbine is 20
bar, 300 0C and the condenser pressure is 0.1 bar. Two feed-water heaters
operate at optimum temperatures of 1500C and 1000C. Determine the quality
of steam at turbine exhaust, cycle efficiency and fraction of steam bleed into
heaters.
[6+10]
2. (a) Derive an expression connecting the height of a chimney and the draught it
produces in terms of temperature of outside air and the mean temperature of
the flue gases.
(b) How much air is used per kg of coal burnt in a boiler having a chimney of 35
m height to create draft of 20 mm of water, when the temperature of the flue
gases in the chimney is 370 0C and the temperature of the boiler house is 34
0C. Take volume of 1 kg of air at NTP as 0.7734 m3. [8+8]
3. A steam turbine develops 160 kW of power with a specific steam consumption
of 19.4 kg/kWh. The steam enters the nozzle at 12 bar, 220 0C and leaves at
1.2 bar. If the diameter of the nozzle at the throat is 7 mm, find the number of
nozzles required. If 8% of the total enthalpy drop is used to overcome friction in
the divergent part of the nozzle, determine the exit diameter of the nozzle and the
condition of the steam leaving the nozzle. [16]
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 and the blade exit angles and relative
velocity coefficients are
1st row moving: 200 and 0.8 ; Fixed row: 250 and 0.85 ; 2nd row moving 300 and
0.9 Find the diagram efficiency under these conditions and the power output for
steam flow rate of 5 kg/s. [16]
5. (a) What are the differences between impulse and reaction turbines? Explain.
(b) A reaction turbine has a speed of 3000 rpm and the mean diameter of blading
at a certain pair is 750 mm. The exit angle of the blade is 200, both fixed
and moving blades being identical. The steam flow rate is 810 kg/min. If the
power developed per pair is 220 kW and the steam pressure is 2.74 bar and
saturated, calculate the inlet blade angle and blade height. [8+8]
6. (a) Differentiate between wet air pump and dry air pump and also derive the
equation for volumetric efficiencies for both the cases.
(b) A surface condenser deals with 2100 kg of steam per hour and the air leakage
amounts to 0.8 kg per hour. The temperature of air pump suction is 35 0C
and the vacuum is 680 mm of Hg when the barometer reads 760 mm of Hg.
Determine the capacity of wet air pump which has a volumetric efficiency of
75%. [8+8]
7. (a) What are essential components required for the operation of gas turbine cycle
and explain their functionality.
(b) What are the advantages and limitations of gas turbine power generation units
in comparison with other power generating units. [8+8]
8. (a) Define and explain the terms:
i. Thrust
ii. Thrust power,
iii. Effective jet exit velocity,
iv. Propulsive efficiency related to turbojet engines.
(b) Describe the nuclear rocket engine with a neat sketch and explain its merits
and demerits.
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