Introduction
Vortex flow meter is a type of volumetric flow meter that makes use of a natural phenomenon that occurs when a liquid flows around a bluff object. Vortex flow meters operate under the vortex shedding principle, where vortices (or eddies) are shed alternately downstream of the object. The frequency of the vortex shedding is directly proportional to the velocity of the liquid flowing through the meter.
Vortex shedding frequency is directly proportional to the velocity of the fluid in the pipe, and therefore to volumetric flow rate. The shedding frequency is independent of fluid properties such as density, viscosity, conductivity, etc., except that the flow must be turbulent for vortex shedding to occur. The relationship between vortex frequency and fluid velocity is:
St = f(d/V)
Where St is the Strouhal number, f is the vortex shedding frequency, d is the width of the bluff body, and V is the average fluid velocity.
Key Advantages
- No Moving Parts: Since vortex flow meters rely on vortex shedding rather than mechanical movement, they have no moving parts, which reduces maintenance and increases reliability.
- Versatility: They can measure various fluids, including gases, liquids, and steam.
- Accuracy: They offer good accuracy and are less affected by changes in fluid density, viscosity, and temperature compared to some other flow meters.
Considerations
- Installation Requirements: Proper installation is crucial for accurate measurements. The flow meter should be installed in a straight section of the pipe with adequate length of straight pipe before and after the meter to ensure stable flow.
- Flow Profile: The flow should be fully developed, which means that the velocity profile should be stable and consistent before the fluid reaches the vortex meter.
In summary, a vortex flow meter works by generating and detecting vortices created by a bluff body placed in the fluid flow. The frequency of vortex shedding is used to determine the flow rate, making vortex flow meters reliable and maintenance-free devices for measuring fluid flow.