How does a Vortex Flowmeter work?

How does a Vortex Flowmeter work?

As a supplier of Vortex Flowmeters, I'm often asked about how these devices operate. Vortex flowmeters are a popular choice in many industries for measuring the flow rate of liquids, gases, and steam. In this blog post, I'll explain the working principle of vortex flowmeters, their advantages, and some key considerations.

Working Principle of Vortex Flowmeters

The operation of a vortex flowmeter is based on the von Kármán vortex street principle. When a fluid (liquid, gas, or steam) flows past a bluff body (also known as a shedder bar) placed in the flow path, it creates alternating vortices on either side of the bluff body. These vortices are shed at a frequency that is directly proportional to the flow velocity of the fluid.

Let's break down the process step by step:

1. Fluid Flow and Bluff Body Interaction: When the fluid approaches the bluff body, it is forced to split and flow around it. As the fluid passes the bluff body, the flow separates from the surface of the bluff body, creating areas of low pressure on either side.
2. Vortex Formation: Due to the pressure differences and the instability of the flow, vortices are formed alternately on the downstream side of the bluff body. These vortices are shed in a regular pattern, creating a von Kármán vortex street.
3. Vortex Frequency Detection: The frequency at which the vortices are shed is detected by a sensor located downstream of the bluff body. This sensor can be a piezoelectric crystal, a strain gauge, or a capacitive sensor. The sensor converts the mechanical vibrations caused by the vortices into an electrical signal.
4. Flow Rate Calculation: The frequency of the electrical signal is then processed by the flowmeter's electronics. Using the known relationship between the vortex shedding frequency and the flow velocity, the flowmeter calculates the flow rate of the fluid. The relationship between the vortex shedding frequency (f), the flow velocity (v), and the width of the bluff body (d) is given by the Strouhal equation:

[f = St \times \frac{v}{d}]

where St is the Strouhal number, which is a dimensionless constant that depends on the shape of the bluff body and the Reynolds number of the flow.

Advantages of Vortex Flowmeters

Vortex flowmeters offer several advantages over other types of flowmeters, which make them a popular choice in many applications:

1. Wide Range of Applications: Vortex flowmeters can be used to measure the flow rate of liquids, gases, and steam. They are suitable for a variety of industries, including chemical, petrochemical, power generation, and food and beverage.
2. High Accuracy: Vortex flowmeters can provide accurate flow measurements over a wide range of flow rates. They typically have an accuracy of ±1% to ±2% of the measured value.
3. Low Pressure Drop: Compared to some other types of flowmeters, such as orifice plates and venturi meters, vortex flowmeters have a relatively low pressure drop. This means that they require less energy to operate, resulting in cost savings.
4. No Moving Parts: Vortex flowmeters have no moving parts, which reduces the risk of mechanical failure and maintenance requirements. They are also less susceptible to wear and tear, making them a reliable choice for long-term use.
5. Digital Output: Most modern vortex flowmeters are equipped with digital output interfaces, such as 4-20 mA, Modbus, or HART. This allows for easy integration with other control systems and data acquisition devices.

Key Considerations for Using Vortex Flowmeters

While vortex flowmeters offer many advantages, there are some key considerations that need to be taken into account when using them:

1. Fluid Properties: The performance of a vortex flowmeter can be affected by the properties of the fluid being measured, such as viscosity, density, and temperature. It is important to select a flowmeter that is suitable for the specific fluid properties.
2. Installation Requirements: Proper installation is crucial for the accurate operation of a vortex flowmeter. The flowmeter should be installed in a straight section of pipe with sufficient upstream and downstream straight pipe lengths to ensure a fully developed flow profile.
3. Vibration and Noise: Vortex flowmeters can be sensitive to vibration and noise, which can affect the accuracy of the measurements. It is important to install the flowmeter in a location where it is not exposed to excessive vibration or noise.
4. Calibration: Like all flowmeters, vortex flowmeters need to be calibrated periodically to ensure accurate measurements. The calibration frequency depends on the application and the accuracy requirements.

Comparison with Other Flowmeters

There are several other types of flowmeters available on the market, each with its own advantages and disadvantages. Let's compare vortex flowmeters with two other popular types of flowmeters: Turbine Flow Meter and LDG Electromagnetic Flowmeter.

1. Turbine Flow Meter: Turbine flow meters measure the flow rate by detecting the rotation of a turbine wheel placed in the flow path. They are suitable for measuring the flow rate of clean liquids and gases. However, turbine flow meters have moving parts, which can be subject to wear and tear, and they require regular maintenance. Vortex flow meters, on the other hand, have no moving parts, which reduces the risk of mechanical failure and maintenance requirements.
2. LDG Electromagnetic Flowmeter: Electromagnetic flow meters measure the flow rate by detecting the voltage induced by the movement of a conductive fluid through a magnetic field. They are suitable for measuring the flow rate of conductive liquids, such as water and wastewater. However, electromagnetic flow meters require a conductive fluid and can be affected by the presence of non-conductive particles or bubbles in the fluid. Vortex flow meters can be used to measure the flow rate of both conductive and non-conductive fluids.

Conclusion

Vortex flowmeters are a reliable and accurate choice for measuring the flow rate of liquids, gases, and steam. Their working principle is based on the von Kármán vortex street principle, which allows for the measurement of flow rate without the need for moving parts. Vortex flowmeters offer several advantages over other types of flowmeters, including a wide range of applications, high accuracy, low pressure drop, and no moving parts. However, there are some key considerations that need to be taken into account when using them, such as fluid properties, installation requirements, vibration and noise, and calibration.

If you are looking for a high-quality Vortex Flowmeter for your application, please don't hesitate to contact us. Our team of experts can help you select the right flowmeter and provide you with the support you need to ensure accurate and reliable flow measurements.

References

1. Miller, R. W. (1996). Flow Measurement Engineering Handbook (3rd ed.). McGraw-Hill.
2. ISO 7145:2005. Measurement of fluid flow in closed conduits - Insertion type vortex flowmeters - Requirements for performance and installation.