Vortex flow meters – what you need to know
If you have steam flow to measure, then you’ve heard of vortex flow meters. But do you really know how they work? Don’t worry. Today we’ll talk about that and more.
You can use vortex flow meters in applications from water to gas, but one of the most common is for steam. Although the multivariable flow meter still rules the roost, some new vortex flow meters have advanced features that make them more appealing than MV solutions.
On the downside, they have certain unavoidable limits, like pressure drop and installation needs. On the upside, you get flexibility, accuracy, and advantages like steam quality measurement. Stick with me to learn more about vortex flow meters!
First, let’s talk about the discovery of the vortex principle and how it came to flow measurement. You should know where your technology comes from.
To do that, let’s go back to 1513. The great Leonardo da Vinci created the first draft of vortices downstream of objects shedding flow. A few years later in 1878, our friend Czech Vincenc Strouhal developed a scientific form to explain the eddies created after bluff bodies. (We’ll talk about those in a minute.) Basically, a wire stretched tight in a jet of air will vibrate, and its frequency is directly proportional to the velocity of the air jet.
This equation will find the Strouhal number, the relationship between the velocity of flow, vortex shedding frequency, and diameter of the bluff body.
In 1912, the physicist Theodore von Kárman used this concept in flow measurement, and we now call his description the Kárman vortex street.
Now that you know the history behind the principle, let’s review how it works to measure flow in your process.
All vortex flow meters have an obstacle, called the bluff body, in front of the measuring sensor. When flow goes through the pipe, the bluff body creates eddies in the vortex street.
The frequency on each side of the bluff body is directly proportional to the flow velocity and volume flow. However, this phenomenon requires a minimum Reynolds number to generate those frequencies.
And what does Reynolds number mean? Well, it has to do with inertial and viscous forces and can forecast the turbulence in the flow. You can read more about that here.
Bluff body types
Vortex flow meters use bluff bodies to break up the flow enough to create eddies. Bluff body types and shapes will vary among vendors. Vendors even have patents for them, because some will result in flow meters offering less pressure loss, others in lower measuring range, and so on.
If you want more details on the pros and cons of each bluff body, I found research with some exciting insights called “Effect of bluff body shape on vortex flow meter performance.” You can read that here.
Volume and mass flow
The vortex flow meter can measure a variety of fluid products. However, the meter itself measures volume flow. So to measure mass, we have additional features to allow accurate measurement.
When you need just the numbers for your volume flow, the meter can measure that directly. For instance, if you have water flow in an application doesn’t have the conductivity a magmeter needs, then you can use a vortex flow meter.
For mass flow, a vortex flow meter must have a component to calculate the measurement as well as a temperature sensor. In some applications, you need a pressure transmitter too. Some vendors build all of these into their vortex meters, and others may only include a couple and have the rest as add-ons. If you need mass flow, then you should check what your vortex meter has to do that.
Sample of market options
I’ll post another article later on installation and advanced features, but now that you have an idea of how vortex flow meters work, I’ll list a few vendors so you can start shopping and thinking about what will suit you best.
We can’t cover all the vendors here, so I invite you to check out more options on Visaya’s device page. We also have tons of product reviews and comparisons, and you’ll find vortex flow meters there too.
Foxboro is a traditional brand in the instrumentation world, owned by Schneider today. The 83S is a universal flow meter, so you can apply it in many processes.
Note: On Schneider’s website there is only the Foxboro model 84 available.
You can read more about it here.
Emerson Automation Solutions has a complete portfolio for vortex flow meters. The Rosemount 8800D brings a bunch of possibilities, with water, flanged, dual, reducer, and high-pressure versions.
You can check it out here.
Endress+Hauser Prowirl F 200
Endress+Hauser has a lot of fancy features in this meter, the “steam specialist.” We reviewed this product, and you can read that here. E+H also has different models to fit your flow application.
Take a look at those here.
Another traditional vendor in instrumentation, Yokogawa didn’t launch many new features with this meter, but it promises reduced costs in your plant, which always sounds good.
The company will fill you in here.
These videos will explain further how vortex flow meters work: