Flow Measurement (Orifice meter)

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
• Kmaxm at Re 200-600

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 (Cc1.0)
• 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

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

14
Reference (cont)

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