SPPU Mechanical Engineering (Semester 6)
Turbo Machines
December 2015
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary


Solve any one question from Q1 and Q2
1 (a) Derive an expression of maximum hydraulic efficiency of Pelton Wheel?
6 M
1 (b) Explain the following terms:
i) Specific speed
ii) Run - away speed.
4 M

2 (a) The inner and outer diameters of the wheel are 1.5 m and 2 m respectively. Water flows outwards over the series of moving vanes attached to the wheel . The wheel runs at 250 rpm. Water is discharged radially at the exit with a velocity of 5 m/s. Work done per kg of water is 250 N-m. The velocity of flow through the runner is constant. Determine:
i) The angles of the moving vane tips
ii) Guide vane angle at inlet
6 M
2 (b) Compare Francis Turbine and Kaplan Turbine.
4 M

Solve any one question from Q3 and Q4
3 (a) Explain the classification of water turbines with examples?
4 M
3 (b) Derive an expression for maximum utilization factor (Diagram efficiency) of Parson's reaction turbine in terms nozzle angle?
6 M

4 (a) Derive an expression of Unit Quantities.
6 M
4 (b) Explain with neat sketch throttle governing of steam turbines?
4 M

Solve any one question from Q5 and Q6
5 (a) Explain the Priming and Cavitation of Centrifugal pump?
8 M
5 (b) A centrifugal pump having outer diameter equal to two times the inner diameter and running at 1000 RPM work against total head of 40 m. The velocity of flow through the runner is constant and equal to 2.5 m/s. The vanes are set back at an angle of 40° at outlet. If the outer diameter of the impeller is 50 cm and width at outlet is 5 cm, Determine:
i) Vane angle at inlet
ii) Workdone by impeller on water per second
iii) Manometric efficiency
10 M

6 (a) Derive an expression of minimum starting speed of centrifugal pump?
8 M
6 (b) A centrifugal pump running at 900 rpm is working against a head 20 m. The external diameter of the impeller is 460 mm and outlet width is 50 mm. If the vanes angles at outlet is 40° and manometric efficiency is 70 % determine.
i) Flow velocity at outlet
ii) Absolute velocity of water leaving the vane
iii) Angle made by the absolute at outlet with the direction of motion at outlet
iv) Rate of flow through the pump
10 M

Solve any one question from Q7 and Q8
7 (a) Explain the terms Surging and Choking in a rotary compressor.
8 M
7 (b) Represent and explain the process involved in centrifugal compressor on (T-S) diagram and derive the expression for isentropic efficiency based on total values.
8 M

8 (a) Explain Slip coefficient and Pressure coefficient.
4 M
8 (b) A centrifugal compressor running at 9000 rpm delivers 600 m 3 /min of free air. The air is compressed from 1 bar and 20° C to a pressure ratio of 4 with an isentropic efficiency of 82%. Blades are radial at outlet of impeller and flow velocity of 62 m/s may be assumed throughout constant. The outer radius of impeller is twice the inner and slip factor may be assumed as 0.9. The blade area coefficient of 0.9 may be assumed at inlet.
Calculate:
i) Final temperature of air
ii) Theoretical power
iii) Impeller diameters at inlet and outlet
iv) Impeller blade angle at inlet
v) Diffuser blade angle at inlet
vi) Breadths of impeller at inlet
4 M

Solve any one question from Q9 and Q10
9 (a) Explain the construction and working of an axial flow compressor.
6 M
9 (b) An axial flow compressor is required to deliver air at the rate of 50 kg/s and provide a total pressure ratio of 5:1 , the inlet stagnation conditions being 288 K and 1 bar. The isentropic efficiency is 86%. The compressor shall have 10 stages with equal rise in total temperature in each stage. The axial velocity of flow is 150 m/s and the blade speed is kept at 200 m/s to minimize noise generation . The stage degree of reaction at mean blade height is 50%. Assuming work done factor as 0.86, calculate all the fluid angles of the first stage. Also calculate the tip and hub diameter if hub-tip diameter ratio is 0.8. Determine the speed in rpm. (R = 287 J/kg K, Cp = 1.005 kJ/kg K).
10 M

Explain the following terms:
10 (a) (i) Stalling in an axial flow compressor.
4 M
10 (a) (ii) Losses in axial flow compressor
4 M
10 (b) Represent and explain the process involved in axial flow compressor on (h-s) diagram and derive an expression for isentropic efficiency and stage pressure ratio.
8 M



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