•Reduction of cross-section of the flowing stream in passing through orifice increases the velocity head at the expense of pressure head
•Reduction of pressure between taps is measured using manometerComplications:
•Formation of Vena-contracta- Fluid stream separates from the downstream side of the orifice plate and forms a free-flowing jet in the downstream side.
•Orifice coefficients are more empirical than those for the Venturi meter.
•Orifice coefficient, generally, is 0.61 in case of flange taps and vena-contracta taps for NRe< 30,000.
•In the process of calculating fluid
velocity with a orifice meter, the velocity of approach is not included.
Velocity through an orifice meter:
- Orifice coefficient
- Ratio of CS areas of upstream to that of down stream
Pa-Pb - Pressure gradient across the orifice meter
- Density of fluid
NOTE: The equation for the velocity of fluid flowing through an orifice meter can be obtained by performing a mechanical energy balance across the pipe
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