• In the upstream cone of the Venturi meter, velocity is increased, pressure is decreased
• Pressure drop in the upstream cone is utilized to measure the rate of flow through the instrument
• Velocity is then decreased and pressure is largely recovered in the down stream cone
• Mostly used for liquids, water
Disadvantages of Venturi meter:
• Highly expensive
•Occupies considerable space (L/D ratio of appr. 50)
•Cannot be altered for measuring
pressure beyond a maximum velocity.
Volumetric flow rate through a Venturi
- Venturi coefficient
Sb - Cross sectional area of down stream
- Ratio of cs areas of upstream to that of down stream.
Pa-Pb - Pressure gradient across the Venturi meter
- Density of fluid
Note: The equation for the volumetric flow rate of fluid through a Venturi meter can be obtained from a mechanical energy balance across the pipe