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1 | P a g e
FLUID MECHANICS AND HYDRAULIC MACHINES
LABORATORY MANUAL
Subject Code : 15A01511
Regulations : JNTUA – R15
Class : V Semester (MECH)
CHADALAWADA RAMANAMMA ENGINEERING COLLEGE (AUTONOMOUS)
Chadalawada Nagar, Renigunta Road, Tirupati – 517 506
Department of Mechanical Engineering
2 | P a g e
CHADALAWADA RAMANAMMA ENGINEERING COLLEGE (AUTONOMOUS)
Chadalawada Nagar, Renigunta Road, Tirupati – 517 506
Department of Mechanical Engineering
INDEX
S. No Name of the Experiment Page No
1 CALIBRATION OF VENTURIMETER 1-5
2 CALIBRATION OF ORIFICE METER 6-10
3 VERIFICATION OF BERNOULLI‟S EQUATION 11-13
4 PERFORMANCE TEST ON PELTON WHEEL 14-17
5 IMPACT OF JETS ON VANES 18-20
6 FRICTION FACTOR OF G.I PIPE LINES
21-23
7 CALIBRATION OF A TRIANGULAR AND RECTANGULAR
NOTCH 24-26
8 PERFORMANCE TEST ON CENTRIFUGAL PUMP 27-29
9 LOSS OF HEAD DUE TO SUDDEN CONTRACTION 30-31
1 | P a g e
EXPERIMENT – 1
CALIBRATION OF VENTURIMETER
1.1 AIM:
To determine the co-efficient of discharge of a given venturimeter.
1.2 APPARATUS:
S. No Equipment
1 Differential U-tube manometer
2 Venturimeter
3 Collecting tank
4 Stopwatch
1.3 THEORY:
Fig – 1.1 Venturimeter
Venturimeter is used to measure the rate of flow through a pipe. Venturimeter consists of a
converging portion, throat and a diverging portion. The function of the converging portion is to
increase the velocity of the fluid and temporarily lower its static pressure. The pressure
difference between inlet and throat is developed. This pressure difference is correlated to the
rate of flow. The expression for theoretical flow rate is obtained by applying the continuity
equation and energy equation at inlet and throat section, and assuming the fluid to be ideal is
given by:
Theoretical discharge, Qth =
√ √
Where,
a1 and a2 = Areas at inlet and throat respectively.
h = Difference in Pressure head
Actual Discharge, Qact =
Where,
A = Cross-section area of collecting tank
2 | P a g e
R = Rise of water level
t = Time taken to rise of water level
Coefficient of discharge, Cd = Qact/Qth
1.4 PROCEDURE:
1. Open the valve of test venturimeter and keep other closed so that water flows from only
venturimeter.
2. Start the pump and adjust the gate valve for steady flow through the venturimeter.
3. Open both the manometer knobs of venturimeter simultaneously.
4. Measure the difference of mercury level in the U-tube manometer (Δ h).
5. Note down the time required for the rise of water level in the measuring tank (t).
6. Conduct this experiment for different gate valve opening and note down the corresponding
flow and manometer readings 1.5 PRECAUTIONS:
1. Remove air from manometer before taking the readings
2. Operate the manometer knobs carefully, so that mercury in manometer does not run away
with water.
1.6 OBSERVATION & TABULAR COLUMN:
Diameter of pipe at inlet (d1) = 25mm = 0.025m.
Diameter of pipe at throat (d2) = 12.5mm = 0.0125m.
Area of inlet (a1) = π d12/4 = _____________ m
2.
Area of throat (a2) = π d22/4 = _____________ m
2.
Rise of water level (R) = _______m
Area of collecting tank (A) = 0.25m X 0.25m = __________m2
S.No.
Difference in
Hg level
Δ h (m)
Pressure head
h = 12.6 x Δ h
(m)
Time taken
for rise of
water level
t (sec)
Qact =AR/t
(m3/s)
Qthe
(m3/s)
Cd =
Qact/Qth
4 | P a g e
1.8 MODEL GRAPH:
Qact
h
Fig - 1.2 (a) Actual discharge Vs Pressure head
Qact
𝒉
Fig - 1.2 (b) Actual discharge Vs 𝐡
Qact
Qth
Fig - 1.2 (c) Actual discharge Vs Theoretical discharge
6 | P a g e
EXPERIMENT – 2
CALIBRATION OF ORIFICE METER
2.1 AIM:
To determine the coefficient of discharge of a given orifice meter.
2.2 APPARATUS:
S. No Equipment
1 Differential U-tube manometer
2 Orifice meter
3 Collecting tank
4 Stopwatch
5 Experiment setup
2.3 THEORY:
It is a device used for measuring the rate of flow of a fluid through a pipe. It is a cheaper
device as compared to venturimeter. It also works on the same principle as that of venturimeter.
It consists of a flat circular plate which has a circular sharp edged hole called orifice, which is
concentric with the pipe. The orifice diameter is kept generally 0.5 times the diameter of the
pipe, though it may vary from 0.4 to 0.8 times the pipe diameter. A differential manometer is
connected at a point, which is at a distance of about 1.5 to 2.0 times the pipe diameter upstream
from the orifice plate and at vena-contracta, which is at a distance of about half the diameter of
the orifice on the downstream side from the orifice plate.
Theoretical Discharge, Qth =
√ √
Where a1 and a2 = Areas at inlet and throat respectively.
h = Difference of Pressure head
Actual Discharge, Qact =
Where,
A = Cross-section area of collecting tank
R = Rise of water level
t = Time taken to rise of water level
Co-efficient of Discharge Cd = Qact/Qth
Fig – 2.1 Orifice Meter
7 | P a g e
2.4 PROCEDURE:
1. Open the valve of test orifice meter and keep other closed so that water flows from single
orifice meter.
2. Start the pump and adjust the gate valve for steady flow through the orifice meter.
3. Open both the manometer knobs of orifice meter simultaneously.
4. Measure the difference of mercury level in the U-tube manometer (Δ h).
5. Note down the time required for the rise of water level in the measuring tank (t).
6. Conduct this experiment for different gate valve opening and note down the corresponding
flow and manometer readings.
2.5 PRECAUTIONS:
1. Remove air from manometer before taking the readings.
2. Operate the manometer knobs carefully, so that mercury in manometer does not run away
with water.
2.6 OBSERVATION & TABULAR COLUMN:
Diameter of pipe at inlet (d1) = 25mm = 0.025m.
Diameter of pipe at throat (d2) = 12.5mm = 0.0125m.
Area of inlet (a1) = π d12/4 = _____________ m
2.
Area of throat (a2) = π d22/4 = _____________ m
2.
Rise of water level (R) = _______m.
Area of collecting tank (A) = 0.25m X 0.25m = __________m2.
S.No.
Difference in
Hg level
Δ h (m)
Pressure head
h = 12.6 x Δ h
(m)
Time taken
for rise of
water level
t (sec)
Qact =AR/t
(m3/s)
Qthe
(m3/s)
Cd =
Qact/Qth
9 | P a g e
2.8 MODEL GRAPHS:
Qact
h
Fig. - 2.1(a) Actual discharge Vs Pressure head
Qact
𝒉
Fig. - 2.1(b) Actual discharge Vs Pressure head
Qact
Qth
Fig. - 2.1(c)Actual discharge Vs Theoretical
discharge
11 | P a g e
EXPERIMENT – 3
VERIFICATION OF BERNOULLI‟S EQUATION
3.1 AIM:
To study and verify Bernoulli‟s equation
3.2 APPARATUS:
S. No Equipment
1 Venturimeter
2 Piezometer
3 Overhead Tank
4 Sump Tank
5 Centrifugal Pump
3.3 THEORY:
Bernoulli‟s theorem states that in a steady ideal flow of an incompressible fluid, the total
energy at any point of the fluid is constant. The Total energy is the sum of Pressure energy,
Kinetic energy and Datum energy. This energy per unit weight of the fluid is called head.
Pressure head = P/ρg
Velocity head = V2/2g
Datum head = z
Thus, mathematically Bernoulli‟s theorem is written as
P/ρg + V2/2g + z = Constant.
3.4 PROCEDURE:
1. Start the pump and open the inlet valve and close the outlet valve.
2. Allow the water to fill in the tank and open the outlet valve so that constant head is
maintained in the tank.
3. Note down the readings in Piezometer at each cross section, which is equal to pressure head.
4. Note down the time required for the rise of water level in the measuring tank (t).
5. Find the velocity at each cross section by using V=Q/a. where, a = area of cross section. And
find velocity head V2/2g.
6. Find out the total head by adding pressure head and velocity head. 3.5 PRECAUTIONS:
1. Ensure that there are no air bubbles in the Piezometers.
2. Perfectly maintain constant head in the tank.
3. Take readings without parallax error.
4. Do not close the outlet and bypass valve completely to avoid strain on the pump.
5. Take rise of water level from the middle of the measuring tank to avoid distortions.
3.6 OBSERVATION & TABULAR COLUMN:
Rise of water level (R) = _______m.
Time take for rise of water level (t) = ___________ s.
Discharge Q = AR/t = ____________ m3/s.
12 | P a g e
S.No Cross section
size
(mm)
Area of Section
a
(m2)
Pressure
Head
X
(m)
Velocity
V = Q/a
(m/s)
Velocity
Head
Y = V2/2g
(m)
Total Head
(X+Y)
(m)
1. 45 X 46
2. 41 X 42
3. 37 X 38
4. 33 X 34
5. 29 X 30
6. 25 X 26
7. 29 X 30
8. 33 X 34
9. 37 X 38
10. 41 X 42
11. 45 X 46
3.7 CALCULATIONS:
13 | P a g e
3.8 MODEL GRAPHS:
Fig. – 3.1(a) Pressure Head Vs Cross section Fig. – 3.1(b) Velocity head Vs Cross section
Fig. – 3.1(c) Total head Vs Cross section
3.9 RESULTS:
Cross section
Pre
ssu
re H
ead
Cross section
Vel
oci
ty h
ead
Cross section
Tota
l h
ead
14 | P a g e
EXPERIMENT – 4
PERFORMANCE TEST ON PELTON WHEEL
4.1 AIM:
To conduct the performance test on Pelton Wheel.
4.2 APPARATUS:
S. No Equipment
1 Pump
2 Pen stock
3 Nozzle and Flow regulating arrangement
4 Runner and buckets
5 Breaking jet and casing
4.3 THEORY:
The Pelton wheel or turbine wheel is a tangential flow impulse turbine. The water strikes the
buckets along the tangent of the runner. The energy available at the inlet of the turbine is only
kinetic energy. The pressure at the inlet and outlet of the turbine is atmospheric pressure.
This turbine is named after L.A. Pelton is an American Engineer. The water form reservoir
flows through the Penstocks at the outlet of which a nozzle is fitted. The nozzle increases the
kinetic energy of the water comes out in the form of a jet and strikes the buckets of runner.
The main parts of the Pelton Wheel are-
i. Nozzle and Flow regulating arrangement
ii. Runner and buckets
iii. Casing and
iv. Breaking jet
Fig. – 4.1 PELTON TURBINE
15 | P a g e
4.4 PROCEDURE:
1. Switch on the pump and adjust the flow valve to maintain the desired pressure at inlet of
nozzle.
2. Now apply the load and note down spring balance readings as W1 and W2 and then note
down the pressure P1 and P2, and the speed (N).
3. Now calculate the discharge (Q) using formula
Q =
√ √
Where Cd = 0.98
a1, a2 are areas of pipe, throat in venturimeter
h is pressure head in meters (P1 – P2)/ρg
4. Calculate the input power using
kW
Where W = 9810 N/m3
Q = Discharge m3/s
H = Pressure head (m)
5. Calculate the output power using
Kw
Where, N is speed in rpm.
T is Torque = W x R N-m.
Where, R = radius of brake drum
W = W1 + W2
Now calculate the efficiency
Output Power / Input Power X 100 %
4.5 PRECAUTIONS:
1. Before starting the experiment, make sure that load is removed at the brake drum.
2. Venturimeter readings should be taken without parallax error.
3. Braking load should be added gradually.
4.6 OBSERVATION & TABULAR COLUMN:
Diameter of inlet for venturimeter (d1) =
Diameter of throat for venturimeter (d2) =
Area of inlet for venturimeter (a1) =
Area of throat for venturimeter (a2) =
Diameter of Jet (d) = 26 mm
Diameter of wheel (D) = 195 mm
Width of bucket = 130 mm
Depth of bucket = 31.2 mm
Radius of brake drum =100 mm
16 | P a g e
S.
No.
Supply
Head
H
Speed
N
(rpm)
Pressure Gauges Readings
(N/m2)
Discharge
Q
(m³/s)
Brake load
W1+W2
Input
Power
(kW)
Output
Power
(kW)
η
(%) P1 P2 h = P1–P2
4.7 CALCULATIONS:
17 | P a g e
4.8 MODEL GRAPHS:
4.9 RESULTS:
N
η
Fig. 4.2(a)Speed Vs Efficiency
Q N
Fig.4.1(b)Discharge Vs Speed
18 | P a g e
EXPERIMENT – 5
IMPACT OF JETS ON VANES
5.1 AIM:
To determine the coefficient of impact of jet vane combination by comparing the actual force
with the theoretical force for stationary vanes of different shapes. They are hemispherical, flat
and inclined vanes.
5.2 APPARATUS:
S. No Equipment
1 Nozzle and flow arrangement.
2 Flat vane, inclined vane and hemispherical vane.
3 Different known masses.
5.3 THEORY:
The liquid comes out in the form of a jet form the outlet of a nozzle which is fitted to a pipe
through which the liquid is flowing under pressure. If some plate, which may be fixed or
moving is placed in the path of the jet on the plate a force is exerted. This force is obtained
from impulse momentum equation. The impact of jet means the force exerted by the jet on the
plate which may be stationary or moving the following cases of the impact of jet i.e. the
force exerted by the jet on the plate will be considered.
a. Force exerted by the jet on a stationary plate when
b. Plate is vertical to the jet.
c. Plate is inclined to the jet
d. Plate is curved.
Force exerted by a jet on fixed flat vertical plate is (Ft) = ρaV2
For inclined plate, the force is (Ft) = ρaV2 sin
2 θ
Plate is curved then the force (Ft) = ρaV2 (1+cosθ)
5.4 PROCEDURE:
1. Connect the required type of the vane and the nozzle.
2. Check whether the nozzle is fixed tightly and balance the vane by adjusting counter weight.
3. Apply some weight (w) to the vane and balance the vane by adjusting pressure and note
down the actual force Fa = w x g.
4. Note down the time required for rise of water level in the measuring tank.
5. Repeat the above steps for different weights and different vanes.
6. Determine co-efficient of impact (or) vane efficiency Ci = Fa / ft
19 | P a g e
5.5 PRECAUTIONS:
1. Before starting the experiment vane should be balanced to zero.
2. Take rise of water level from the middle of the measuring tank to avoid distortions.
3. Take pressure gauge readings without parallax error.
5.6 OBSERVATION & TABULAR COLUMN:
Diameter of nozzle (d) = ___________
Area of nozzle (a) = = __________
Rise of Water level (R) = ___________
Area of collecting tank (A) = 0.3 m X 0.3 m = __________
Co
-eff
icie
nt
of
imp
act
(CI)
= F
a/F
t
Th
eore
tica
l
Fo
rce
(Ft)
Vel
oci
ty V
=
Q /
a
Dis
char
ge
Q =
AR
/ t
Tim
e ta
ken
for
10
cm
Ris
e o
f w
ater
„t‟
(sec
)
Act
ual
Fo
rce
Fa
(N)
Pre
ssu
re g
aug
e
Rea
din
g
(Kg
/cm
2)
Dia
of
No
zzle
d
(m)
20 | P a g e
Ty
pe
of
van
e
Sl.
No
.
5.7 CALCULATIONS:
5.8 MODEL GRAPHS:
5.9 RESULTS:
Fa
Ft
Fig. – 5.1 Actual Force Vs Theoretical Force
21 | P a g e
EXPERIMENT – 6
FRICTION FACTOR OF G.I PIPE LINES
6.1 AIM:
To study the flow in pipes (G.I) and determine friction factor for a given pipes.
6.2 APPARATUS:
S. No Equipment
1 Collecting tank
2 Differential U-tube manometer
3 Stopwatch
4 Experiment setup
6.3 THEORY:
When a fluid flows through pipes, it experiences some resistance due to which some of energy
of fluid is lost. This loss of energy is classified as
1. Major Energy losses
2. Minor Energy losses
Major losses are due to friction between fluid and pipe material.
Head lost due to friction is calculated by
Where, hf = head lost due to friction
4f = friction factor
L = Length of pipe
v = velocity of flow
d = diameter of pipe
The friction factor depends on the pipe material and the fluid flowing through the pipe
Fig. – 6.1 Losses due to Friction
22 | P a g e
6.4 PROCEDURE:
1. Switch on the pump and open the gate valve of pipe (say 1 inch pipe) and keep other valves
closed.
2. Open the corresponding manometer knobs and remove the entrapped air in the manometer
pipes.
3. Note down the difference in mercury level in the manometer.
4. Note down time for rise of water level in the collecting tank.
5. Repeat the same procedure for other pipes.
6.5 PRECAUTIONS:
1. All the entrapped air from manometer is driven out so that mercury in monometer does not
run away with water.
2. Don‟t close the bypass valve full or open it fully care should be taken while operating the
bypass valve.
3. Take the manometer readings after eliminating air bubbles.
4. Take rise of water level from the middle of the measuring tank to avoid distortions.
6.6 OBSERVATION & TABULAR COLUMN:
Rise of Water level (R) = ___________
Area of collecting tank (A) = 0.25 m X 0.25 m = __________
Discharge (Q) = AR/t
S. No.
Diameter of
pipe
d (m)
Area
a (m2)
Time for rise of
water level
t (s)
Discharge
(Q)
Velocity
v = Q/a
Loss of
Head
hf
Co-efficient
of friction
4f
23 | P a g e
6.7 CALCULATIONS:
6.8 MODEL GRAPHS:
6.9 RESULTS:
v2
hf
Fig. – 6.2(a) Head lost Vs Velocity2
v
hf
Fig. – 6.2(b) Head lost Vs Velocity
24 | P a g e
EXPERIMENT – 7
CALIBRATION OF A TRIANGULAR AND RECTANGULAR NOTCH
7.1 AIM:
To calculate the coefficient of discharge for rectangular and triangular notch.
7.2 APPARATUS:
S. No Equipment
1 Stopwatch
2 Experiment setup
7.3 THEORY:
A notch is a device used for measuring the rate of flow of liquid through a small channel or a
tank. It may be defined as an opening in the side of a tank or a small channel in such a way that
the liquid surface in the tank or channel is below the top edge of the opening.
Discharge through a rectangular notch is given by
√
Discharge through a triangular notch is given by
(
)√
Fig. – 7.1 Triangular Notch
7.4 PROCEDURE:
1. Start the system and arrange to flow some water in it.
2. By using vernier calipers calculate the head of water over crest (H2)
3. And the head of water over nappe called H1.
4. Total head H = H2 – H1.
25 | P a g e
5. Calculate the time taken for 10cm rise of water in tank.
6. Theoretical discharge is calculate by using Qt = 2/3 x L x √2g H3/2
7. Actual discharge is calculate by taking the formula Qa = (A x R)/t, where a = External Area
of tank
8. Coefficient of discharge is calculated by taking the ratio of Qact to Qthe.
7.5 PRECAUTIONS:
1. The vernier calipers tip is exactly on the top of the water surface.
2. Water from the measuring tank is allowed to discharge into the regenerating tank after
noting down the time taken for 10cm rise of water
7.6 OBSERVATION & TABULAR COLUMN:
Area of measuring tank (A) = 0.3 m X 0.3 m = _____________ m2
Rise of water level in collecting tank (R) = _____________ m2
Qact =
m
3/s
S.No.
Net Head
H = (H1 – H2)
Time taken
for Rise of
water
t (sec)
Theoretical Discharge
Qth (m3/s)
Actual Discharge
Qact (m3/s)
Cd =
Qact / Qth
H1 H2 H
7.7 CALCULATIONS:
26 | P a g e
7.8 MODEL GRAPHS:
7.9 RESULTS:
Qact
Qth
Fig. – 7.2 Actual discharge Vs Theoretical discharge
27 | P a g e
EXPERIMENT – 8
PERFORMANCE TEST ON CENTRIFUGAL PUMP 8.1 AIM:
To conduct test on a single stage centrifugal pump at rated speed to obtain pump characteristics
8.2 APPARATUS:
S. No Equipment
1 Centrifugal pump
2 Collecting tank
3 Sump
4 Stop watch
5 vacuum gauge
6 pressure gauge
8.3 THEORY:
The hydraulic machines which convert the mechanical energy into hydraulic energy are called
pumps. The hydraulic energy is in the form of pressure energy. If the mechanical energy is
converted into pressure energy by means of centrifugal force acting on the fluid then, the
hydraulic machine is called centrifugal pump.
The centrifugal pump acts as a reverse of an inward radical flow reaction turbine. This means
that the flow in the centrifugal pump is in the radial outward directions. The centrifugal pump
works on the principle of forced vortex flow which means that when a certain mass of liquid is
rotated by an external source, rise in pressure head at any point of the rotating liquid takes
place.
The rise is pressure head at any point of the rotating liquid is proportional to the square of the
tangential velocity of the liquid at that point.
Thus at outlet of the impeller where the radius is more, the rise in pressure head will be more
and the liquid will be discharged at the outlet with a high pressure head.
Centrifugal pump has four main ports. They are impeller, casing, suction pipe with a foot valve
and a strainer delivery pipe.
Fig. – 8.1 Single Stage Centrifugal Pump
28 | P a g e
8.4 PROCEDURE:
1. Fill up sufficient water in the sump tank
2. Trine the pump with water required
3. Keep the discharge valve completely open
4. Start the pump and adjust the discharge valves to the required pressure
5. Note down the following readings
a. Pressure gauge reading
b. vacuum gauge
c. input power i.e., voltages current
d. speed of pump
e. Time for 10 cm rise of water
6. Empty the discharge as soon as the reading is over by opening drain valve
7. Carry out the above procedure of the some speed and for different charges by regulating the
discharge valve and adjust input power
Specifications: - 1. Impeller diameter – 39 mm
2. RPM =
3. Head range = 8 – 12 m
Motor = 180 and 4.5A, 0.74kw, 300RPM
4. collecting tank
5. Piezometer and drain valve = 30cmX30cm
6. Section pipe diameter (ds) = 25mm
8.5 PRECAUTIONS:
1. Prime the pump before starting the motor.
2. Readings should be taken without parallax error.
3. Don‟t run the pump dry.
29 | P a g e
8.6 TABULAR COLUMN:
S.
No.
Pressure
gauge
reading
Vacuum
gauge
reading
Time
taken for 5
rev of
energy
Meter disc
Time taken
for rise of
water In
collecting
tank
Total
head
P + V
(m)
Discharge
Q
(m3/s)
Input
Power
(kW)
Out put
Power
(kW)
η
(%)
8.7 CALCULATIONS:
8.8 MODEL GRAPHS:
Total head Vs Discharge
Input power (KW) Vs Discharge (m3/sec)
Output power (KW) Vs Discharge (m3/3)
Efficiency (n) Vs Discharge (m3/3)
Total head (m) Vs speed (m)
Output power (KW) Vs speed (m)
8.9 RESULTS:
30 | P a g e
EXPERIMENT – 9
LOSS OF HEAD DUE TO SUDDEN CONTRACTION 9.1 AIM:
To determine the coefficient of loss in sudden contraction.
9.2 APPARATUS:
S. No Equipment
1 Experimental set-up
2 Stopwatch
9.3 PROCEDURE:
1. Start the pump keeping the delivery valve close. Make sure that ball valve is fully open
which is at the collecting tank.
2. Slowly open the cocks which are fitted at sudden contraction end and make sure that
manometer is free from air bubbles.
3. Make sure while taking readings, that the manometer is properly primed. Priming is the
operating of filling the Manometer upper part and the connecting pipes with water venting
the air from the pipes. Note down the loss of head “hc” from the manometer scale.
4. Note down the time required for the rise of 10cm (i.e. 0.01m) water in the collecting tank by
using stop watch. Calculate discharge using below formula.
Discharge: - The time taken to collect some „x‟ cm of water in the collecting tank in m³/sec.
A x R
Q = t
A = area of the collecting tank in m² (0.3m X 0.3m)
R = rise of water level taken in meters (say 0.1m or 10cm)
t = time taken for rise of water level to rise „r‟ in„t‟ seconds.
5. Calculate the velocity of the jet by following formula
V = Q/A m/sec
A = cross sectional area of the pipe= d² /4
d =diameter of the pipe
6. Calculate the coefficient of contraction for the given pipe by
[
]
Where:-
hc - Loss of head due to sudden contraction.
Cc- Coefficient of contraction.
V - Average velocity of flow in m/sec
7. Repeat the steps 2 to 6 for different sets of readings by regulating the discharge valve.