Download Hydraulic Machines Question Bank PDF

TitleHydraulic Machines Question Bank
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Page 1

Question Bank on Hydraulic Machines (AM601)

ON DIAMENSIONAL SIMILARITY & MODEL ANALYSIS:

1. A radial flow hydraulic turbine is required to be designed to produce 30MW under a head
of 14m at a speed of 95 rpm. A geometrically similar model with an output of 40KW and
a head of 5m is to be tested under dynamically similar conditions. At what speed, must
the model be run? What is the required impeller diameter ratio between the model and
prototype and what is the volume flow rate through the model if its efficiency can be
assumed to be 90%?

[Ans. 721.4 rpm, 0.079, 0.906m3/s]


2. Specification for an axial flow coolant pump for one loop of a pressurized water nuclear
reactor:
Head=85m. Flow rate=20,000m3/hr., Speed= 1490 rpm, Diameter=1.2m, Water
density=714 kg/m3, Power=4MW (electrical).
The manufacture plants to build up a model of the above. Test conditions limit the
available electrical power to 500kW and flow to 1.5m3/s of cold water. If the model and
prototype efficiencies are assumed equal, find the head (H2/H1), Speed (N2/N1) and scale
ratio (D2/D1) of the model. Calculate the ‘dimensionless specific speed’ of the prototype
and confirm that it is identical with the model.

[Ans. 1.0, 3.3, 0.3, 2.35 radian]


3. A projected low head hydro-electric scheme is to be set up, where 283.17 m3/s of water
are available under a head of 3.66 m. Alternative schemes to use Francis turbines having
a specific speed of 467.5 or Kaplan turbines with a specific speed of 804.1 rpm(Metric
HP)0.5/m5/4 are investigated. The normal running speed is to be 50 rpm. In both the cases.
Determine the dimensionless specific speeds and compare the two proposals in so far as
the numbers of the machines are concerned. Estimate the power developed by each
machine. The units in either installation are to be of equal power and the efficiency of
each type may be assumed to be 0.9.

[Ans. 2.5 radian for Francis, 4.3 radian for Kaplan, 1716
kW per Francis turbine, 5209 kW per Kaplan turbine, 6
Francis machines, 2 Kaplan machines]

ON PELTON TURBINE:

1. A generator is to be driven by a small Pelton wheel with a head of 91.5m at inlet to the
nozzle and discharge of 0.04m3/s. The wheel rotates at 720 rpm. And the velocity co-
efficient of the nozzle is 0.98. If the efficiency of the wheel (based on the energy
available at the nozzle is 80% and the ration of bucket speed to jet speed is 0.46,

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determine the wheel –to jet- diameter ratio at the centre-line of the buckets, and the speed
of the wheel. What is the dimensionless power specific speed of the wheel?

[Ans. 14.5, 19.1 m/s, 0.082 radian]


2. A reservoir with a height of 280m. is connected to the power house of a hydroelectric
plant through three pipes each 2.5 kg long and with friction factor (f)= 0.006, in which
the head loss is not exceed 34m. it is a requirement that a total shaft output of 18MW be
developed, and to achieve this, it is decided to install a number of single-jet Pelton
wheels, each with a dimensionless specific speed not exceeding 0.23 radian. The ratio of
bucket speed to jet speed is 0.46, while the wheel speed is to be 650 rpm. If the nozzle
have a discharge coefficient (Ku1) of 0.49 and the velocity co-efficient (Kv1) of 0.96and
assuming that each wheel has an overall efficiency of 87%, find: (a) the no. of Pelton
wheels required, (b) the wheel diameter, (c) the jet nozzle diameter and (d) the diameter
of supply pipes.

[Ans. 6, 0.901m., 0.174m., 1.07m]


3. The buckets of a Pelton wheel deflect the jet through an angle of 1700, while the relative
velocity of the water is reduced by 12% due to bucket friction. Calculate the theoretical
hydraulic efficiency from the velocity triangles for a bucket to jet speed ratio of 0.47.
Under a gross head of 600m the wheel develops 1250 kW, when the loss of head due to
pipe friction between the reservoir and nozzle is 48m. The bucket-circle diameter of the
wheel is 900mm and there are two jets. The nozzle velocity coefficient is 0.98. Find the
speed of rotation of the wheel and the diameter of the nozzles if the actual hydraulic
efficiency is 0.9 times that calculated above.

[Ans. 93%, 1017 rpm, 42.3mm]


4. A twin-jet Pelton turbine has a mean bucket-circle diameter of 1.68 m. and runs at
500rpm. When the jets are 152.5 mm diameter, the available head at the nozzle is 488m.
Assuming coefficient of velocity for the nozzle as 0.98, outlet angle of bucket 150,
relative velocity for water leaving the bucket 0.88 of that of inlet; and windage and
mechanical losses 3% of the water horse-power supplied, find: (a) the water horsepower
supplied and break horsepower: (b) the force of one jet on the bucket: (c) the overall
efficiency.
Note: 1HP = 0.746 kW, 1 kgf = 9.81 N. Students may convert answers in SI units
accordingly.

[Ans. 22.740 HP; 19.300 HP; 17,000kgf; 84.7%]


5. A Pelton wheel is working under a gross head of 400m. The water is supplied the
penstock of diameter 1m. and length 4 km, from reservoir to the Pelton wheel. The co-
efficient of friction for the penstock is given as 0.008. The jet of water of diameter

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[Ans. 81.54%]

6. An inward flow radial turbine has an overall efficiency of 74%.the net head across the
turbine is 5.5mand the required power output is 125kw.the runner tangential velocity is
0.97(2gh)1/2,while the flow velocity is 0.42(2gh)1/2.if the speed of the runner is 230rpm ,
with hydraulic loss accounting for 18%of the energy available ,calculate the inlet guide
vane exit angle ,the inlet angle of the runner vane, the runner diameter at the inlet and the
height of the runner at the inlet . Assume that the discharge is radial.

[Ans. 43.40, 143.80, 0.836m, 0.287m]

7. A Francis turbine has a diameter of 1.4m,and rotates at speed 430rpm.water enter the runner
without shock with a flow velocity of 9.5m/s and leave the runner without whirl with an
absolute velocity of 79 m/s and leaves the runner without whirl with an absolute velocity of
7 m/s. the difference between the sum of the static and potential heads at entrance to the
runner and the exit from the runner is 62m. If the turbine develop 12.25 MW and has a flow
rate of 12m3/s of the water then the net head is 115m., find (a)the absolute velocity of water
at entry to the runner and the angle of inlet guide vanes ,(b)the entry angle of the runner
blade and (c)the head lost in the runner .

[Ans. 33.8m/s, 16.30, 84.60, 13.7m]

8. An inward flow reaction turbine runs at speed of 375rpm. Under an available net total head
from inlet flange to tailrace of 62m.the external diameter of the runner is 1.5m.and the
dimensionless power specific speed based on the power transfer to the runner is
0.14rev.water enter the runner without shock with a flow velocity of 7m/s. it discharge to
the tailrace with a velocity of 2m/s. the static pressure head is 2.2m.below atmospheric
pressure .assuming a hydraulic efficiency of 90%,find (a)the runner blade entry angle
,(b)the head lost in the absolute casing and guide vanes ,in the runner and in the draft tube
and (c)the draft tube entry diameter.

[Ans. 140.40, 3.27m, 0.92m, 1.8m of water , 0.88mm]

9. (a) Show that the hydraulic efficiency h for a Francis turbine having velocity of flow
through runner as constant, is given by the equation


2

1

0.5 tan
1

tan
1

tan

h






 
 

  
 
 



where, α =guide blade angle & θ =runner vane angle at inlet .the turbine is having radial
discharge at outlet.

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(b) If vanes are radial at inlet, show that 2
2

2 tanh








10. The following data is given for a Francis turbine: net head=70m, speed=600rpm, shaft
power=367.875 kW, overall efficiency =85%, hydraulic efficiency 95%, flow ratio=0.25,
breadth ratio=0.1, outer diameter of the runner =2×inner diameter of the runner. The
thickness of the vanes occupy10%of the circumferential area of the runner. Velocity of flow
is constant at inlet and the outlet and discharge is radial at outlet. Determine (a) guide blade
angle (b) runner vane angle at inlet and outlet (c) diameter of runner at inlet and outlet (d)
width of wheel at inlet.

[Ans. 12020’, 18057’, 0.49m, 0.245m, 49mm]

11. A reaction turbine work at 500rpm.under a head of 100m.the diameter of turbine at inlet is
100cm.and the flow area is 0.35m2.the angle made by absolute and relative velocity at inlet
are 150 and 600 with the tangential velocity .determine (a)the volume flow rate (b)the power
developed (c)efficiency ,assume whirl at outlet to be zero.

[Ans. 2.90m3/s, 2355.4kw, 82.6%]

12. A conical draft tube having inlet and outlet diameters 1m and 1.5m.discharges water at
outlet with a velocity of 2.5m/s. the total length of the draft tube is 6m.and 1.2m.of the
length of the draft tube is immersed in water .if the atmospheric draft tube is equal to 0.2into
velocity head at the outlet of the tube, find (a) pressure head at the inlet and (b) efficiency of
the draft tube.

[Ans. 4.27m. absolute, 76.3%]

ON KAPLAN TURBINE:

1. An axial flow hydraulic turbine has a net head of 23 m. across it, and, when running at a
speed of 150 rpm, develops 23MW. The blade tip and hub diameter are 4.75 m. and 2.0
m. respectively. If the hydraulic efficiency is93%and the overall efficiency85%, calculate
the inlet and outlet blade angle at the mean radius assuming axial flow at outlet.

[Ans. 156.20, 17.20]


2. A Kaplan turbines operating under a net head of 20 m. develop 16MW with an overall
efficiency of 80%. The diameter of the runner is 4.2 m. while the hub diameter is 2 m.
and the ‘dimensionless power specific speed’ is 3 radian. If the hydraulic efficiency is
90% calculate the inlet and exit angles of the runner blades at the tip and at the hub if the
flow leaving the runner is purely axial.

[Ans. 163.40, 14.50; 127.60, 28.60]

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