Venturimeter

Principle of Venturimeter:

• Based on Bernoulli’s theorem. The fluid’s velocity increases, and pressure decreases as it passes through the throat of the Venturimeter.

Formula:

$Q = C_d A_1 \sqrt{\frac{2\Delta P}{\rho \left(1 – \left(\frac{A_2}{A_1}\right)^2 \right)}}$

• Where:
  • Q = flow rate
  • Cd​ = discharge coefficient
  • A1​ = cross-sectional area of the pipe before the converging section
  • A2​ = cross-sectional area of the throat
  • ΔP = pressure difference between the inlet and the throat
  • ρ = fluid density

Construction of Venturimeter:

1. Converging Section: Narrows the fluid flow.
2. Throat: The narrowest section where velocity is highest, and pressure is lowest.
3. Diverging Section: Gradually returns the pipe to its original diameter.
4. Pressure Taps: Located before the converging section and at the throat.

Working of Venturimeter:

• Fluid enters the Venturimeter and is accelerated in the converging section.
• Maximum velocity and minimum pressure occur at the throat.
• Pressure recovery occurs in the diverging section.
• The pressure difference between the inlet and throat is measured to calculate the flow rate.

Uses:

• Measurement of flow rates in large pipelines.
• Common in water supply systems, gas pipelines, and in various industrial processes.

Advantages:

• High accuracy and reliability.
• Low permanent pressure loss compared to orifice meters.
• Suitable for a wide range of fluid types, including dirty or sediment-laden fluids.

Disadvantages:

• More expensive and complex to install.
• Requires a longer straight pipe section upstream and downstream for accurate measurements.
• Bulky and not suitable for small-diameter pipes.

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