Hydraulic Machinery - May 2012

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.

Answer any four of the following questions:-

1 (a) Explain the difference between impulse and reaction turbines.(5 marks) 1 (b) What is the importance of the governing of the turbine? How is it done in Kaplan turbine?(5 marks) 1 (c) What is the function of air vessel in reciprocating pump?(5 marks) 1 (d) What are the advantages and disadvantages of hydroelectric power plant over other types of power plant?(5 marks) 1 (e) What is priming in centrifugal pump? Why is it necessary?(5 marks) 2 (a) A single jet Pelton wheel turbine is required to drive a generator to develop 10000kW. The available head at the nozzle is 760m. Assume the following: Electric generation efficiency 95%. Pelton wheel efficiency is 87%, coefficient of velocity for nozzle is 0.97, mean bucket velocity 0.46 of jet velocity, outlet angle of bucket 15° and the relative velocity of water leaving the bucket 0.85 of that of inlet. Find:-
i) Diameter of jet
ii) Flow in m³/s
iii) Force exerted by jet on the buckets(14 marks) 2 (b) Why are Pelton turbines not suitable for low heads and high discharges.(6 marks) 3 (a) Calculate the leading dimensions of the runner of an inward flow reaction turbine to develop 750KW under a head of 100m assuming the following data:
Guide vane angle=18°
Axial length of blade at inlet=0.1 times outer diameter
Outlet diameter=0.6 time the inlet diameter
Radial velocity of flow=constant
Final discharge=Radial
Hydraulic efficiency=0.88
Overall efficiency=0.86
Allowance for blade thickness=5%
Speed in rpm=1000(16 marks) 3 (b) Explain the function of guide vanes in reaction turbine.(4 marks) 4 (a) The following data refer to an elbow type draft tube:
Area of circular inlet=25m²
Area of rectangular outlet=116m²
Velocity of water at inlet to draft tube=10m/s
Efficiency of draft tube=70%
Height of draft tube inlet above tail race=0.6m
Calculate:
i) Vacuum at inlet to draft tube
ii) Power wasted in the draft tube
iii) Power lost to tail race(12 marks) 4 (b) What is meant by cavitation? What is Thoma's cavitation factor, what is its significance for water turbines?(8 marks) 5 (a) A centrifugal pump is required to discharge 0.2m³ of water against a head of 22m when the impeller rotates at a speed of 1500rpm. The manometric efficiency is 75%. The loss of head in pump in meters due to fluid resistance is 0.03V₂² where V₂ is the velocity of water leaving the impeller in m/s. The area of the impeller outlet surface is 1.2D₂² in m², where D₂ is the impeller diameter in m.
Determine:
i) The impeller diameter
ii) Outlet vane angle
Assume that the water enters the impeller without whirl.(14 marks) 5 (b) What is NPSH? What is the difference between NPSH available and NPSH required?(6 marks) 6 (a) A single acting reciprocating pump has a plunger of 80mm diameter and a stroke is 150mm. It takes its supply of water from a sump 3m below the pump through a pipe 4.5m long and 30mm diameter. It delivers water to a tank 12m above the pump through a pipe of 25mm diameter and 15m long. If separation occurs at 78.48KN/m² below atmospheric pressure, find the maximum speed at which the pump may be operated without separation, assume the plunger to have simple harmonic motion.(12 marks) 6 (b) Write short note on performance characteristic of reciprocating pump.(8 marks) 7 (a) A centrifugal pump runs at 1440rpm. The impeller is 40cm in diameter and 2.5cm wide at outlet. The pump lifts water through height of 30m of which suction lift is 2.5m. The suction and delivery pipes are 30cm in diameter. The losses due to friction in suction and delivery pipes are 1.5m and 5.5m respectively. The exit blade angle is 25°. Assume the flow to be radial at inlet and manometric efficiency of 84%.
Calculate:
i) Quantity of water flowing
ii) Pressure at suction and delivery end of pump if atmospheric pressure is 10.35m of water.(14 marks) 7 (b) What is a multistage pump? Discuss the variation of pressure head and velocity in the successive stages in multistage pumps.(6 marks)