Vortex vs. Turbine Flow Meters: A Detailed Comparison

This article dives into the differences between two common types of flow meters: vortex flow meters and turbine flow meters. We’ll explore how each works, their features, and advantages.

Vortex Flow Meter

How it Works

Vortex flow meters utilize a natural phenomenon that occurs when a fluid flows around a “bluff” object. Think of it like a flag flapping in the breeze. As the fluid flows, vortices are shed alternately downstream of the object. The faster the fluid flows, the more frequently these vortices are shed. This “shedding” frequency is directly proportional to the velocity of the fluid. Therefore, a higher shedding frequency indicates a higher flow rate.

A vortex flow meter consists of two main parts: the flow tube and the transmitter. The flow tube itself has three key components: the body, the shedder (the bluff object), and sensors to detect the vortices.

Key Features of Vortex Flow Meters

• Pipe Sizes: Typically range from 2” to 20”.
• Suitable Fluids: Can handle clean to dirty water.
• Pressure Loss: Exhibits low to medium pressure loss.
• Accuracy: Generally around +/-1% of full scale.
• Upstream Straight Pipe Requirement: Needs 10 times the pipe diameter of straight pipe before the meter.
• Downstream Straight Pipe Requirement: Needs 5 times the pipe diameter of straight pipe after the meter.
• Cost: Generally considered to be low to medium in cost.

Turbine Flow Meter

How it Works

Turbine flow meters use a small turbine wheel placed directly in the path of the fluid flow. They are classified as volumetric flow meters. As the fluid flows, it causes the turbine blades to rotate. Each blade forms part of a magnetic circuit, producing a voltage based on the following equations:

|E| = b m Wr

Where:

• m = number of blades
• b = amplitude of angular variation in magnetic flux (in Wb)
• Wr = angular velocity of the wheel (in radians)

The frequency of this generated voltage is proportional to the angular velocity of the blade:

f = (m Wr) / (2 π)

The output voltage takes the form of a sine wave, and the frequency of this wave is directly related to the speed of the turbine, which in turn is related to the fluid flow rate.

Key Advantages of Turbine Flow Meters

• Good Dynamic Response: They can respond quickly to changes in flow rate.
• Accurate Totalized Flow Measurement: They can measure the total amount of fluid that has passed through the meter with high accuracy.

Summary

In summary, both vortex and turbine flow meters offer effective ways to measure fluid flow, but they operate on different principles and have distinct characteristics. Vortex flow meters are more robust for varying fluid conditions, while turbine flow meters are known for their dynamic response and accuracy in totalized flow measurement. The choice between the two will depend on the specific requirements of your application.