Hydraulic Machinery - May 2013

Mechanical Engineering (Semester 6)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.

Write notes on:-

1 (a) Slip and on classification of reciprocating pumps.(5 marks) 1 (b) Degree of reaction in turbines.(5 marks) 1 (c) Causes, Effects and remedies of cavitation in turbines.(5 marks) 1 (d) Self priming pumps.(5 marks) 2 (a) A single jet pelton turbine is required to generate 2000KW. The total head from the reservoir to the entry of nozzle is 250m. The blade angle at outlet is 15°, and the reduction in the relative velocity while passing over the blade is 5%. The coefficient of velocity is 0.98, speed ratio 0.46 and mechanical efficiency 95%. The head loss in the penstock is 10m.
i) Determine the overall efficiency
ii) Draw the velocity triangles at the inlet and outlet of the bucket
iii) Find the force exerted by the jet on the buckets
iv) Determine the energy lost due to the jet at bucket exit
v) Determine the jet diameter(15 marks) 2 (b) Write a note on determination of the operating points for series and parallel operation of centrifugal pumps.(5 marks) 3 (a) In a inward flow vertical shaft turbine the inlet blade angle is 115°, velocities of flow at inlet and outlet are 6.5m/s and 6m/s respectively, discharge is 10m³/s, losses in the runner 0.9m, hydraulic efficiency 90%, speed is 225rpm and net head 24m. For radial discharge determine:
i) Diameter of runner at inlet
ii) Degree of reaction if loss in casing and guide vanes is 5m(15 marks) 3 (b) Write a note on affinity laws for a pump.(5 marks) 4 (a) A Kaplan turbine is filled aerofoil blades and has a speed of 120rpm. The mean radius of the blade circle is 1.5m and the length in the radial direction is 0.5m. The inlet and outlet blade angle are 113° and 63° respectively and the chord length is 2.5m. The values of C_L and C_D are 0.7 and 0.04 respectively.The turbine is supplied with water under a head of 10m. If the flow ratio is 0.357. Determine:
i) Overall efficiency
ii) Drag(15 marks) 4 (b) Write a note on the different types of casing used in centrifugal pumps.(5 marks) 5 (a) A one tenth scale model is tested under a head of 7m. The actual turbine will work under a head of 12m with a speed of 120rpm and will develop 1015KW. The efficiency of the prototype is 92%. Neglecting scale effect determine:
i)The flow rate of the model and prototype
ii)Speed and power output of the model
If the difference in efficiencies between model and prototype is three percent determine:
iii)Speed and power output of the model(14 marks) 5 (b) Why are Pelton turbines not suitable for low heads and high discharges.(6 marks) 6 (a) A centrifugal pump has outlet diameter 175mm, outlet width 50mm and outlet angle 29°. The head characteristics are given by H=43.5+258Q-3770Q² where Q is in m³/s and H in m. The mechanical efficiency of the pump is 0.96. The pump is used to deliver water through a pipe of diameter 300mm, 800m long the static lift being 24.5m. The friction coefficient 4f=0.03. The speed is 2880rpm. Do not neglect velocity head.
Determine:
i)Discharge
ii)Power input to pump(10 marks) 6 (b) A double acting reciprocating pump has a piston of diameter 220mm and a stroke of length 600mm. It sucks water from a sump. In which the level of water is 4m below the centre line of the pump. The length of the suction pipe is 6.5m with diameter 150mm. The friction factor 4f is 0.024 and separation occurs at 2.4m of water absolute. Determine the maximum speed of the pump when there is
i)No air vessel on the suction side
ii)A large air vessel on the suction side close to the cylinder(10 marks) 7 (a) The table below shows head, discharge and efficiency of a centrifugal pump running at constant speed of 800rpm. It delivers water through a static head of 16m. The total length of pipe is 1200m and the pipe diameter is 280mm.
i)Discharge
ii)Input power
When two such pumps are working in parallel. Take 4f=0.026