1. Flow Measurement (Orifice meter)by
Ashfaq Md. Ansery

2. Orifice meter
It may be installed in pipeline with a minimum of trouble and expense

3. Orifice meter

4. Orifice meter

5. Theory (Orifice meter)

6. Variation of K with Re

7. Variation of K with Re (cont)
At high Reynolds number K is essentially constant, but as Reynolds number is lowered, K is also increased
K~maxm at Re=

8. Variation of K with Re (cont)
The lowering of Reynolds number increases viscous action which causes a decrease in Cv and an increase in Cc
The latter apparently predominates over the former until Cc reaches its maximum value (about to 1)
With further decrease in Re, ‘K’ then becomes smaller because Cv continues to decrease

9. Placement of Pressure Tap

10. Difference between an Orifice meter and Venturimeter
For venturi tube, there is no contraction-
Area of the jet is always equal to the area of the throat and is fixed
While for the orifice the area of the jet is a variable
(less than Ao, the area of the orifice)

11. Difference between an Orifice meter and Venturimeter
For venturitube
Cd = Cv (Cc=1.0)
While for the orifice, it is much more affected by variations in Cc than it is by variations in Cv

12. Orifice meter Disadvantage Its practical disadvantage is that-
it offers greater frictional resistances as compared to venturimeter

13. Reference Robert L. Daugherty
Chapter 12, Fluid Measurements
FLUID MECHANICS with Engineering Applications
(SI Metric Addition)
Robert L. Daugherty
Joseph B. Franzini
E. John Finnemore

14. Chapter 15, Flow Measurement, Page 440-447
Reference (cont…)
Chapter 15, Flow Measurement, Page
Applied Fluid Mechanics (5th Edition)
Robert L. Mott