orifice meter

Orifice Meter

Merchant Institute Of Technology,Piludara

Prepared By :-Bhavsar Dhyan

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.

Orifice meter

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.

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.

12

xDirectionof flow

Orifice

Differential manometer

2D D/2 Vena contracta

Discharge in orifice meter

Discharge in orifice meterLet 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 22

1 2 g

2g

g

2g

p1

v1

z

p

v2

z

2

22 2

2 2

22 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.

Let A0 is the area of the orifice.

Coefficient of contraction, cC A2

A0

1 20 cA C vA1

By continuity equation, we have

A1v1 A2v2

v

Hence,2 2

2

2 c

A2C 2v2

A1

2ghC 2A

1

v

2gh 0 c 2

v 2

1 A0


Thus, discharge,2

2 cC 2A1

Q A2v2 v2

A0Cc

A0Cc

2gh

1 A0

If Cd is the co-efficient of discharge for orifice meter, which is defined as

2

21 A0

2

2

2

2

2

2

d c

c

c

A1

C 2A1

C 2A1

A1

C C

1 A0

1 A0

Cc Cd

1 A0


Hence,

The coefficient of discharge of the orifice meter is much smaller than that of a venturimeter.

Discharge in orifice meterd

A0 A1

2ghQ C A2 A2

10

Orifice meter

Thank You

orifice meter

Engineering