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Venturi meter:

• 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 meter:

                         where  Cv - 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

Return to the index of flow meters

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