VIGNAN’S ENGINEERING COLLEGE::VADLAMUDI
Exp No:
Date:
FRANCIS TURBINE
AIM:
a) To study the constant head characteristics of Francis turbine.
b) To study the operating characteristics of Francis turbine.
c) To determine the specific speed.
DESCRIPTION:
Francis turbine is a radial inward flow reaction turbine. This has the advantage
of centrifugal force acting against the flow.
The turbine consists of (1) Runner (2) A ring of adjustable guide vane (3) An in
volute casing (4) Draft tube.
The runner consists of two rings with a number of curved vanes in between
them. The guide vanes can be rotated about their axis by means of a hand wheel and
their position is indicated by a pair of dummy guide vanes fixed outside the turbine
casing.
A 15 HP centrifugal pump supplies water under pressure to the turbine. The
flow from the pump can be controlled by means of gate valve fitted in the pipeline.
The pressure water from the pump enters through the guide vanes and then to the
runner, while passing through the spiral casing and guide vanes. The position of the
pressure head is converted into velocity head in the pipeline.
When the water passes through the valves of the runner, remaining head is
converted into the velocity head. Due to the proper curvature of the vanes, velocity
energy is transformed into mechanical energy and hence the runner is rotated.
The water through the runner is discharged into the draft tube thereby to the
tailrace. The discharge through the runner can be regulated by operating the guide
vanes.
Francis turbine is best suited for medium head say 30m to 40m. The specific
speed ranges room 55 to 300.
The discharge in pipe lines and hence through turbines can be measured with
venturimeter fitted in the pipeline. A mercury differential manometer accompanies the
venturimeter.
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VIGNAN’S ENGINEERING COLLEGE::VADLAMUDI
Output of the turbine is determined by means of the rope brake. The head of
water is measured by pressure on vacuum gauge.
TECHNICAL SPECIFICATIONS:
I. Francis turbine
1. Rated supply head
15.0 meters.
2. Discharge
2000 lpm.
3. Rated speed
1250 rpm.
4. Unit speed
51.5 rpm.
5. Specific speed
95.5 rpm.
6. Runner diameter
150 mm.
7. No. of guide vanes
8
8. P.C.D. of guide vanes
220 mm.
9. Brake rope diameter
16 mm or (12mm).
10. Brake drum diameter
300 mm.
II. Supply Pumpset:
1. Rated head
20.0 meters.
2. Discharge
2000 rpm
3. Normal speed
1440 rpm
4. Power required
15 hp. (11.2 KW)
5. Size of pump
100 x 100 mm
6. Type
Centrifugal medium Single suction volt
7. Impeller diameter
280 mm.
III. Flow measuring unit:
1. Size of venturimeter
…
100 mm
2. venturimeter area ratio …
0.35
…
0.55
venturimeter
…
59.16 mm
For Orificemeter
…
74.16 mm
…
200 (210)
orificemeter area ratio
1. Throat diameter for
4. Inlet cone angle for
venturimeter
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VIGNAN’S ENGINEERING COLLEGE::VADLAMUDI
5. Diverging cone angle
…
100 (140)
6. Manometer
…
Double column, differential type.
7. Flow recording range
…
upto 2,500 lpm.
Venturimeter
…
k= 0.0131(Qa = kh)
For Orificemeter
…
k= 93.0
8. Meter constant for
(Qa = kh)
THEORY:
a) Discharge formula for venturimeter Q = 0.0131 h
h - - difference in the levels of manometer in terms of water head
b) total head = H = G + V + Z
where G = pressure head
V = vacuum head
Z = Height of pressure gauge over vacuum gauge.
c) Input to the turbine
IP =
gQH
1000
KW.
d) Output
Brake drum diameter
= 0.3m
Rope diameter
= 0.01m
Equivalent drum diameter = 0.31m
Load weight
= W1 kg
Spring weight
= W2 kg
Resultant load = W1 - W2
=W kg
Speed of turbine
=N rpm
2NT
KW
60,000
output BP
e) Efficiency (o) =

input
IP
BP =
f) Specific speed: it can be defined as the speed in rpm of a turbine which will
develop 1 hp under unit head
Ns =
N P
H 5/4
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VIGNAN’S ENGINEERING COLLEGE::VADLAMUDI
PROCEDURE: (for constant head)
1. Prime the pump with water and start the pump.
2. Gradually open the delivery valve of the pump
3. Adjust the guide vane opening at 1/5 of the opening by operating the hand wheel.
4. The head should be made constant by operating the delivery valve and the head
should be maintained at a constant value.
5. Observe the speed of the wheel using the tachometer.
6. Observe the reading h1 and h2 corresponding to the fluid level in the two
manometer limbs which is connected to the venturimeter.
7. Adjust the load on the brake drum to vary the speed of the drum and record the
readings from the tachometer, weight added and spring balance.
8. Repeat step 7 for getting at least six sets of reading
9. Repeat the experiment for
2 3 4
, , and full opening of the nozzle.
5 5 5
Experimental procedure (constant speed method)
1. Close the delivery valve of the pump.
2. Prime the pump with water and start the motor.
3. Gradually open the delivery valve of the pump and adjust the guide vane position
at
1
of the opening.
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4. Read the pressure gauge and note down the value.
5. Apply the load on the brake drum so that the speed shown by the tachometer
comes to the rated speed and note this rated speed. Note down the tension W1 and
W2 indicated by the spring balances attached to the brake drum.
6. Observe and note the readings of the manometer limbs.
7. Manipulate the discharge through pressure valve and control the speed at the rated
valve through hanger weights and note the reading of the spring balance.
8. Observe and note down the manometer reading h1 & h2.
9. Repeat the experiment for
2 3 4
, , and full opening of the nozzle.
5 5 5
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VIGNAN’S ENGINEERING COLLEGE::VADLAMUDI
OBSERVATION TABLE:
S.No
Gate
opening
Manometer
readings in
m of
Mercury
h1
h2
5
Speed
N, rpm
Spring balance
reading in kg
W1 W2 W1-W2
VIGNAN’S ENGINEERING COLLEGE::VADLAMUDI
CALCULATION TABLE:
S.No
Gate
opening
H in m
of
water
Q=KH
m3/s
6
BP
IP

NS
NU
PU
QU
VIGNAN’S ENGINEERING COLLEGE::VADLAMUDI
PRECAUTIONS:
1. Prime the centrifugal pump before starting
2. Set the gate opening carefully.
3. Never try to throttle the suction side of the pump to control discharge as it
would seriously affect the performance of the pump.
GRAPHS: Nu Vs Qu,
Nu Vs Pu, Nu Vs o
RESULT:
QUESTIONS & DISCUSSION:
1. What way is Francis turbine different from pelton wheel and Kaplan turbine?
2. What is specific speed? How does the knowledge of the value of Ns for turbine
help in selection of the type of turbine?
3. What is the function of spiral casing of turbine.
4. What is the purpose of draft tube? Why should it be divergent? Why cannot we
have a greater angle of divergence? Why cannot we extend the length of the tube
more and more? What will happen if some air leaks in the entrance of the draft
tube?
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