FLUID MACHINERY,University Of Pune Question Paper,T.E. (Mechanical) (Semester – II),2010 Question Paper

University Of Pune Question Paper
T.E. (Mechanical) (Semester – II) Examination, 2010
FLUID MACHINERY (2003 Course)
Time : 3 Hours Max. Marks : 100
Instructions : 1) Answers to the two Sections should be written in separate
books.
2) Neat diagrams must be drawn wherever necessary.
3) Black figures to the right indicate full marks.
4) Use of logarithmic tables, slide rule, Mollier charts, electronic
pocket calculator and steam tables is allowed.
5) Assume suitable data, if necessary.
SECTION – I
Unit – I
1. a) What are hydrodynamic machines ? Explain different efficiencies of hydrodynamic
machines. 8
b) A jet of water coming out of 10 cm diameter nozzle strikes a moving blade
with a velocity of 15 m/s horizontally and tangentially. The blade is also moving
with a velocity of 5 m/s in same direction as that of jet. The blade is so shaped
that the jet is deflected through 145°. Neglecting the friction loss over the
surface of the blade, find the following :
i) Force exerted by the jet on the vane in the direction of its motion
ii) Power developed
iii) Efficiency of the blade. 8
OR
2. a) A jet of water coming out from a nozzle of 2.5 cm diameter with a velocity
7.5 m/s strikes to hinged rectangular plate of 20 cm height whose point of action
is 12 cm below the hinge.
i) Determine the horizontal force required to be applied at the C.G. of the
plate to maintain the plate in vertical position.
ii) Find the required velocity of the jet if the plate is deflected through 25° to
the vertical and the same force acts on the plate at its C.G. and along the
same direction of original. The C.G. of the plate is 10 cm below the hinge
and its weight is 60 N. 8
b) Show that when a jet of water impinges on a series of curved vanes, maximum
efficiency is obtained when the vane is semi-circular in section and the velocity
of the vane is half that at the jet. 8
Unit – II
3. a) With the help of neat sketch describe the main components of a pelton turbine.
What are the limitations of a pelton turbine ? 8
b) A pelton wheel is operated by supplying water through a gross head of 500 m.
The penstock carrying water from the dam to nozzle is 1m in diameter and
5 km long. The coefficient of friction for the penstock pipe is 0.008. The nozzle
diameter supplying the water is 15 cm and it is deflected through 165° by the
buckets. Because of friction, the velocity in the bucket passage is reduced by
15%. Find the power developed by the pelton wheel and brake power if the
mechanical efficiency is 90%. Also find the hydraulic efficiency and over all
efficiency. Take velocity ratio as 0.45. 8
OR
4. a) Prove that the maximum hydraulic efficiency of a pelton wheel is given by
Cv k1[ cos ] 2
1 2
hyd.max . =η θ+ where blade friction coefficient,
1
2
Vr
Vr K = and
Cv is the coefficient of velocity. 8
b) The following data refers to an outward flow impulse turbine
Inner diameter = 1.75 m
Outer diameter = 2 m
Speed = 300 rpm
No. of vanes = 30
Vane tip thickness = 2 cm at inlet, 3 cm at outlet
Width of runner = 25 cm at inlet, 20 cm at outlet
Flow rate = 6 m3/s
Calculate moving vane angles at inlet and exit for a radial discharge at exit, if
velocity of coefficient, Cv = 0.98. 8
Unit – III
5. a) Differentiate between inward radial flow and outward radial flow reaction
turbine. Why inward radial flow reaction turbines are preferred in practice ? 6
b) What is degree of reaction ? Explain its significance. 4
c) A reaction turbine works at 450 rpm under a head of 115 m. The diameter of
runner at inlet is 1.2 m and flow area of 0.4 m2
. At the inlet the absolute and
relative velocities make angle of 20° and 60° respectively with tangential velocity.
Determine runner power and hydraulic efficiency. Assume the velocity of whirl
at the outlet to be zero. 8
OR
6. a) What is cavitation ? On what factors does the cavitation in reaction turbines
depend ? Explain the methods to avoid cavitations in water turbines. 9
b) A conical draft tube attached to a francis turbine has an inlet diameter of 3 m
and its area at exit of 20 m2. Water enters the draft tube with a velocity of 5 m/s.
The inlet of draft tube is 5 m above the tail race level. If the frictional loss in
the draft tube is 5% of the velocity head at outlet, find :
ii) Total head at inlet considering tail race level as datum
iii) Power of water at exit of runner
iv) Power lost to tail race
v) Power lost in the draft tube. 9
SECTION – II
Unit – IV
7. a) What do you understand by characteristic curves of a turbine ? Discuss different
operating characteristic curves for reaction turbines. 8
b) The following data refers to a turbine at 200 rpm with full gate opening :
Head M 7.5 6.78 6.18 5.67 5.22 4.8
Power KW 266 231 201 176 153 131
Efficiency % 81.1 83.1 84.4 84.6 85.0 84.1
Draw graph of unit power and efficiency against unit speed. How much water
is required per second for maximum output under a head of 6.3 m ? 10
OR
8. a) A francis turbine of diameter 3 m develops 7000KW at 300rpm when the head
available is 50 m. A model of scale 1 : 8 is to be tested in the laboratory where
the head available is 10 m. Find the size, speed, discharge and power developed
by the model. Assume overall efficiency for both is 0.8. Also find
specific speed for both. 8
b) Derive on expression for specific speed of a water turbine. What is its effect
on the shape of runner in the water turbine ? 5
c) Define specific speed of a pump and explain its importance particularly for
model testing. 5
Unit – V
9. a) What is cavitation and causes for creating the cavitation in centrifugal pump ?
Explain the effects of cavitation and methods of its preventation. 8
b) A centrifugal pump is coupled with diesel engine and running at 1000 rpm.
The water enters the pump radially and the velocity of flow is constant through
the impeller. The inside and outside diameters of the pump are 20 cm and 40 cm
respectively. The inlet and exit blade angles are 20°C and 30°C. Width of the
vane at inlet is 2cm. Take overall efficiency as 70% and mechanical efficiency
as 90%. Neglecting losses and blade thickness, calculate discharge
through the pump and power input given by the diesel engine. 8
OR
10. a) The following table gives head discharge characteristics of a centrifugal pump
at constant speed.
'Q' lpm 0 200 400 600 800 1000 12000
'H' m 15 14.6 13.2 11.0 8.4 7.2 5.8
% 0 46 71 78 70 62 50
Two such pumps are connected in parallel with common suction and delivery
pipes to operate against a static lift of 7.5 m. The frictional external losses to
the pump are given by 2.05Q2
×10–6 m where ‘Q’ is the discharge in lpm.
Calculate the discharge, head and power required to drive the pumps when :
i) Only one pump is operated
ii) Two identical pumps are operated in parallel. 16
η
Unit – VI
11. a) Explain construction and working of a hydraulic torque converter with the
help of neat sketch. 8
b) A hydraulic ram delivers water at the rate of 5 litres/sec to a tank located at 40 m
from the ram. The water is supplied to the ram from a tank of 5 m height from
ram at a rate of 50 litres/sec. The length and diameter of the delivery pipe are
60 m and 6 cm respectively. Find the D’Aubuisson and Ronkine efficiencies
of the ram. Take F = 0.01 for delivery pipe. 8
OR
12. Write short notes on : 16
i) Airlift pump
ii) Regenerative pump
iii) Deep well pump
iv) Fluid coupling.
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