It gives a brief information of orifice meter.

1. Orifice Meter
Merchant Institute Of
Technology,Piludara
Prepared By :-
Bhavsar Dhyan

2. Orifice meter
 The venturi meter described earlier is a reliable flow
measuring device.
 Furthermore, it causes little pressure loss.
 For these reasons it is widely used, particularly for large-
volume liquid and gas flows.
 However this meter is relatively complex to construct and
hence expensive.
 Especially for small pipelines, its cost seems
prohibitive, so simpler devices such as orifice meters
are used.

3. Orifice meter

4. Orifice meter
 It is also known as Pipe orifice & Orifice plate.
 It may be installed in pipeline with a
minimum of trouble and expense.
 Pipe orifice is a device used for measuring the
rate of flow of a fluid through a pipe.
 It consists of a thin,circular plate with a hole
in it.

5. Orifice meter
 The plate is held in the pipeline
between two flanges.
 Pipe orifice is a cheaper device as
compared to venturimeter.
 The diameter of orifice is generally 0.5
times the diameter of the pipe (D),
although it may vary from 0.4 to 0.8
times the pipe diameter.

6. 1
2
x
Direction
of flow
Orifice
Differential manometer
2D D/2 Vena contracta
Discharge in orifice meter

7. Discharge in orifice meter
Let d1 = diameter at section 1
p1 = pressure at section 1
v1 = velocity at section 1
A1= area at section1
d2, p2, v2, A2 are the corresponding values at section 2.
Applying Bernoulli’s equations at sections 1 and 2, we get
2 2
2
1 2
g 2g g 2g
p1

v1
 z 
p

v2
 z
2 2
2 2
2 2
2
2 1
2g
2g
 v v1

 p1   p
 z   z  g 1   g 2 
   
v1
 h 
v2
 v  2gh v where h is the differential head.

8. Let A0 is the area of the orifice.
Coefficient of contraction, cC 
A2
A0
1 2
0 cA C
v
A1
By continuity equation, we have
A1v1  A2v2
 v 
Hence,
2 2
2
2 c
A2
C2
v2
A1
2gh
C2
A1
v  2gh  0 c 2
 v 2 
1
A0
Discharge in orifice meter

9. Thus, discharge, 2
2 c
C2
A1
Q  A2v2  v2 A0Cc
A0Cc 2gh

1
A0
If Cd is the co-efficient of discharge for orifice meter, which is defined as
2
2
1
A0
2
2
2
2
2
2
d c
c
c
A1
C2
A1
C2
A1
A1
C  C
1
A0
1
A0
 Cc  Cd
1
A0
Discharge in orifice meter

10. Hence,
The coefficient of discharge of the orifice meter is much
smaller than that of a venturimeter.
Discharge in orifice meter
d
A0 A1 2gh
Q C
A2
 A2
1 0

11. Orifice meter

12. Thank You