EXPERIMENT NO:9
CALIBRATION OF ORIFICE METER
OBJECTIVE:
To determine the Co-efficient of discharge of orifice meter Cd.
THEORY:
An orificemeter is a simple device used for the measuring the discharge through pipes. Orifice meter also works on the same principle as that of Venturimeter i.e., by reducing the cross – sectional area of flow passage, a pressure difference between the two sections before and after orifice is developed and the measurement of the pressure difference enables the determination of the discharge through the pipe. However, an orifice meter is an economical 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 orificemeter may be used for the measured of discharge through pipes.
EXPERIMENTAL SET UP:
1. Measuring tank to measurethe flow rate.
2. A pipe line with a Orifice meter.
3. Tapping with ball valves are provided at inlet & outlet of rifice meter and these are connected to Manometer.
4. A constant steady supply of water with a means of varying the flow rate using monoblock pump.
5. Stop watch with float switch for measurement of flow rate by collecting fixed quantity of water.
PROCEDURE:
1. Fill-in the sump tank with clean water
2. Keep the delivery valve closed.
3. Connect the power cable to 1 Ph, 220V, 10Amps with earth connection.
4. Switch – on the pump & open the delivery valve.
5. Adjust the flow through the control valves of the pipe line.
6. Open the corresponding ball valves of the pipe line.
7. Note down the differential head reading in the manometer (expel if any air is there by opening the drain cocks provided with the manometer).
8.Operate the butterfly valve to note down the collecting tank reading against the known time and keep it open when the reading are not taken.
9. Change the flow rate & repeat the experiment.
PRECAUTIONS:
1. Do not start the pump if the voltage is less than 180 V.
2. Do not forget to give electrical neutral & earth connections correctly.
3. Frequently (at least once in three months) Grease / Oil the rotating parts.
4. Initially, put clean water free from foreign material, and change once in three months.
5. At least every week, operate the unit for five minutes to prevent clogging of the moving parts.
CALCULATIONS:
S.No / Pressure Readings / Time taken for 25cm riseR cm / Qthe / Qact / Cd
P1kg/cm2 / P2 kg/cm2
Area of measuring tank A = 0.13 m2
Acceleration due to gravity g = 9.81m/sec2
Diameter at vena contracta d = 12.5mm
Diameter of inlet to orifice meter D= 25mm
- Theoretical discharge
a1xa2√2gH
Qth = ------m3/sec
√ (a12-a22)
Where
a1 =area of inlet to orifice meter = ?D2/4 in m2
a2 =area at vena contracta = ?d2/4 in m2
H= (P1-p2) kg/cm2
= (P1-p2) x9.81/10-4 N/m2
= (P1-p2) x 9.81x104 m of water
ρH2ox g
= (P1-p2) x 9.81x104
103 x 9.81
H = (P1-p2) x 10 m of water
- ACTUAL DISCHARGE
A X R
Qact= ------m3/Sec
100 X t
WHERE, A = Area of measuring tank in m
R=rise of water level in m
t = time taken in seconds for rise of water.
- CO-EFFICIENT OF DISCHARGE:
Actual discharge Qact
Cd = ------= ------
Theoretical discharge Qth
RESULT: Co- efficient of discharge orifice meter Cd ______
ORIFICE METER
FAQ’sfor LAB
1.What is the reason for smaller value of C d ?
2.What is Orifice meter?
3.What is the principle of Orifice meter?
4.What are the parts of Orifice meter?
5.What is the thickness of the plate?
6.What is the range of bevel angle in orifice meter?
7.What is the diameter of the orifice?
8.Where two pressure taps are provided?
9.Where upstream pressure tap is located?
10.What is vena contracta?
REFERENCES
Reference Books
1.Fluid Mechanics and Fluid Power Engineering by D.S. Kumar, Kotaria & Sons.
2. Fluid Mechanics and Machinery by D. Rama Durgaiah, New Age International.
3. Hydraulic Machines by Banga & Sharma, Khanna Publishers.
4.Fluid Mechanics and Hydraluic Machines by R.K.Bansal ,Lakshmi Publications