Calibration of an Orificemeter
B141753, B141758, B141860, B141812, B141866
July 12, 2019
1
Aim
To determine the coefficient of discharge through Orifice meter.
2
Apparatus Required
• Orifice meter
• Differential U tube
• Collecting tank
• stop watch
• Scale
3
Introduction
An orifice meter is another simple device used for measuring the discharge through a pipe. Orifice meter also
works on the same principle as that of venturimeter i.e. by reducing the cross sectional area of the flow passage a
pressure difference between the two sections is developed and the measurement of the pressure difference enables
the determination of the discharge through the pipe.An orifice meter is a cheaper arrangement for discharge
measurement through pipes and its installation requires a smaller length, as compared with venturimeter. As
such where the space is limited, the orifice meter may be used for discharge of through pipes.
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Principle
Orifice meter is a device used to measure discharge in a pipeline or a closed conduit.Orifice is a hole through
which liquid is made to pass through it.It works on Bernouli’s principle or venturi effect and continuity equation.
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Theory
Orifice meter consists of a flat plate with a circular hole at the centre. The circular hole is called ”orifice”.The
edges of the orifice are bevelled.The orifice plate is fixed using flanges.The section of flow where the area is
minimimum is called ”venacontracta”. At venacontracta the velocity is maximum.
The thickness of the plate is less than an equal to 0.05 times the diameter of the pipe. The diameter of the
orifice may vary from 0.2 to 0.85 times the pipe diameter but generally the diameter is kept as 0.5 times pipe
diameter. Two pressure taps are provided at section 1 on the upstream side of the orifice plate and other at
section 2 on the downstream side of the orifice plate since in the case of an orifice change in the cross section
as area of the flow passage is provided and there being a gradual change in the cross sectional area of the flow
passage as in the case of venturimeter there is a gradual loss of energy in a orifice meter than in a venturimeter.
1
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Formulae
h=Difference of head in meter of water.
h = (h1 − h2 ) ∗ [ SSno − 1]
Where,
h1 = Upper limit of the mercury.
h2 = Lower limit of the mercury.
Sn = Specific gravity of mercury.
So = Specific gravity of flowing fluid.
ath = A∗R
t
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Procedure
1. Fill in the sump tank with clean water.
2. Keep the delivery valve closed.
3. Connect the power cable to 1 Ph, 220 V, 10 Amps with earth connection.
4. Switch ON the pump and open the delivery valve.
5. Open the corresponding ball valve of the orificemeter pipe, keeping the valve of venturimeter closed.
6. Adjust the flow through the control valve of the pump.
7. Open the corresponding ball valves fitted to orificemeter tappings.
8. Expel if any air is there by opening the drain cocks provided with the manometer and note down the
differential head reading in the manometer.
9. Close the Butterfly Valve of the collecting tank and note down the time taken for 10c.m rise of water level
10. Keep the butterfly valve open when the readings are not taken.
11. Change the flow rate and repeat the steps 3 to 7 for 5 different flow rates.
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Specifications/Given Data
• Electric service : 220-240 V AC, 1-Phase, 50Hz with earth connections
• Motor : 1.5 HP, 1420 RPM
• Supply pipe of 25mm
• Orificemeter size inlet 25mm and throat 14mm
• Manometer scale 300mm
• Measuring tank dimensions:300mm x 300mm
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Observation Table and Data
S.no
1
2
3
4
5
Time rate for
10cm water
level
35
24
22
18
16
Actual
charge
dis-
2.5 ∗ 10− 4
3.75 ∗ 10− 4
4.09 ∗ 10− 4
5 ∗ 10− 4
5.625 ∗ 10− 4
Table 1: Observation Table
Differential head mm of Hg
5.3
4
3.5
2
1.5
7.4
8.3
9
10
11
2
0.2646
0.5418
0.819
1.008
1.197
Theoretical
discharge
coefficient of
discharge
3.67 ∗ 10− 4
5.25 ∗ 10− 4
6.45 ∗ 10− 4
7.15 ∗ 10− 4
7.8 ∗ 10− 4
0.7
0.71
0.63
0.69
0.72
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Calculations
Discharge:
Q( act) = (A ∗ R)/t
√
√
Q( th) = [(a1 ∗ a2 ) (2gh)/ (a1 )2 − (a2 )2 ]
Cd = Q( act)/Q( th)
Where
a1 = Area of the venturi at the inlet,
a2 =Area of the venturi at the throat,
g=Acceleration due to gravity (9.81 m/s),
d1 =Inlet diameter in meters,
d2 =Throat diameter in meters,
Q = Discharge in m3 /s
(1)
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Result
Average coefficient of discharge is 0.69
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Precautions
1.Check whether all joints are water proof and tight.
2.Fill the manometer to about half the height with mercury.
3.Check proper electrical connections to the switch which internally connected to the motor.
4.While taking the height or rise of water, keen observation is required.
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Viva voice Questions
1. What is the main aim of the experiment?
2. What is the working principle of Orificemeter?
3. What are the losses on account of flow through a orificemeter?x
4. What is co-efficient of discharge?
5. What is priming of a pump? Why it is necessary to prime a pump?
3