Principle
Based on Bernoulli's theorem. The fluid's velocity increases, and pressure decreases as it passes through the throat of the Venturi meter.
Formula
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
Converging Section: Narrows the fluid flow.
Throat: The narrowest section where velocity is highest, and pressure is lowest.
Diverging Section: Gradually returns the pipe to its original diameter.
Pressure Taps: Located before the converging section and at the throat.
Working
Fluid enters the Venturi meter 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.