Flow MeasurementFlow Measurement(Orifice meter)(Orifice meter)

bybyAshfaq Md. AnseryAshfaq Md. Ansery

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

Orifice meter

Orifice meter

Theory (Orifice meter)

Variation of K with Re

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= 200-600

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

Placement of Pressure Tap

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)

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

Orifice meter DisadvantageIts practical disadvantage is

that-it offers greater

frictional resistances as compared to venturimeter

Reference

Chapter 12, Fluid MeasurementsFLUID MECHANICS with Engineering Applications

(SI Metric Addition)

Robert L. Daugherty Joseph B. Franzini

E. John Finnemore

Reference (cont…)

Chapter 15, Flow Measurement, Page 440-447

Applied Fluid Mechanics (5th Edition)Robert L. Mott