GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- V (New) EXAMINATION - WINTER 2019
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Subject Code: 2150102 Date: 02/12/2019Subject Name: Fundamentals of Turbo Machines
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
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2. Make suitable assumptions wherever necessary.3. Figures to the right indicate full marks.
Q.1 (a) Enlist classification of turbomachines. 03
(b) Discuss choking in turbomachines. 04
(c) Draw velocity triangle for an axial turbine stage. 07
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Q.2 (a) Define Degree of reaction, flow coefficient and loading coefficient. 03
(b) Define: design condition, off design condition, matching point and 04
equilibrium running point w.r.t. turbomachines.
(c) Explain the need of multistaging of turbomachines in jet engines. Draw 07
velocity triangle for pressure compounded turbines.
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OR(c) Draw h-s diagram for an axial turbine stage. 07
Q.3 (a) Differentiate an impulse stage and a reaction stage. 03
(b) Prove that Cyz + Cy3 = Wy2 + Wy3 for axial turbine. 04
(c) Air at the rate of 2Kg/s enters the impeller of a centrifugal compressor in 07
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axial direction. The stagnation temperature and stagnation pressure at inletare 300K and 1bar. The rotor has 20 radial vanes and rotates at 15000rpm.
The stagnation pressure ratio between diffuser outlet and impeller inlet is 4.2
and the overall efficiency is 83%. Mechanical efficiency is 96%, density at
impeller outlet is 2Kg/m?, calculate power required to drive the compressor
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and the impeller tip radius. Width at impeller exit is 12mm. determineabsolute Mach number at that point. Slip factor is 0.88.
OR
Q.3 (a) Which are the different impellers used in centrifugal compressor stage. 03
(b) Draw velocity triangle for centrifugal compressor stage. 04
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(c) Draw h-s diagram for centrifugal compressor stage. 07 Q.4 (a) Enlist losses occurs in turbomachines. 03
(b) Draw and explain the velocity triangle for stage of axial compressor. 04
(c) Following data refers to mean section of free vortex axial turbine stage hub 07
diameter 460mm, tip diameter 780mm, rotational speed 6000rpm, absolute
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velocity at rotor entry is 267 m/s, air angles at rotor entry and exit 75° and45° respectively, axial velocity is constant and is 70m/s, calculate followings
for the hub section.
1. Air angles and blade angles,
2. Degree of reaction,
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3. Flow coefficient,4. Loading coefficient and Work done by the turbine
OR
Q.4 (a) Enlist benefits of axial machines over radial machines. 03
Q.4 (b) Draw schematic of centrifugal compressor used in jet engines. 04
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Q.5 (a) For an axial flow compressor stage, the mean diameter of the stage is 03
25cm, the pressure ratio developed by the machine is 1.3. Determine the blade and
air angle if the mean flow velocity was 200m/s. condition at inlet are 1bar
and 300K.
(b) Discuss surge in a compressor stage. 04
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(c) What is degree of reaction? Derive its expression for axial turbine stage. 07OR
Q.5 (a) A multistage gas turbine is to be designed with impulse stages, and is to 03
operate with an inlet pressure and temperature of 6 bar and 900 K and at
outlet pressure of 1 bar. The isentropic efficiency of the turbine is 85%. All
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the stages are to have a nozzle outlet angle of 75° and equal outlet and inletblade angles. Mean blade speed of 250 m/s and equal inlet and outlet gas
velocities. Estimate the number of stages required considering optimum
blade to gas speed ratio.
(b) Define utilization factor, wok done factor and slip factor. 04
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(c) Draw velocity triangle for ninety degree IFR turbine. 07The flow of air at 20m/s enters to the nozzle with pressure 6bar and
temperature 900K. The mass flow rate of air is 10Kg/s, find inlet Mach
number, the stagnation and static pressure and temperature at nozzle exit if
mach number at the exit is limited to 0.7.
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