Understanding Vortex Shedding Flow Technology

Foxboro Vortex Shedding Flowmeter.
Notice the shedder bar in the flow path.

Photograph of vortices
(credit Jürgen Wagner via Wikipedia)

Vortex shedding flowmeters are a type of flowmeter available to the process industry for the consistent evaluation of flow rates. These flowmeters measure the volumetric flow rate of media such as steam flowing in pipes, gases, and low viscosity liquids, boasting both versatility and dependability. Since they have no moving parts, they are impervious to the kind of wear turbine or mechanical meters experience.

Principles of Operation
A "shedder" bar (also known as a bluff body) in the path of

Animation of vortices
(credit Cesareo de La Rosa Siqueira
via Wikipedia)

the flowing fluid produces flow disturbances called vortices. The resulting vortex trail is predictable and proportional to the fluid flow rate. This phenomena is know as the "Von Kármán vortex street" (see illustrations to the right). Sensitive electronic sensors downstream of the shedder bar measures the frequency of the vortices and produce a small electrical pulse with every vortex created. The electrical pulses also also proportional to fluid velocity and is the basis for calculating a volumetric flow rate, using the cross sectional area of the flow measuring device.

Typical Areas of Use
Vortex shedding flowmeters are used on steam, cryogenic liquids, hydrocarbons, air, feed water, and industrial gases.

Applications to Avoid
Splitting higher viscosity fluids into concordant vertices is extremely difficult due to the internal friction present, so using vortex shedding flowmeters on high viscosity media should be avoided. Also, avoid applications with low flow rates and low Reynolds Numbers, as the vortices created are unstable.

Consideration for Use
Consideration must be given to applications with low Reynolds numbers, as the generation of vortices declines at critical points of reduced velocity. Low pressure can also be a problem in this regard. Users must take Reynolds number, velocity, and density into consideration before choosing a vortex shedding flow meter. As always, it's best to discuss your application with an knowledgable support professional before specifying, purchasing, or installing this type of flowmeter.

Watch the video below for more information on vortex flow technology.

For more information on  vortex shedding flowmeters, visit https://www.meadobrien.com or call (800) 892-2769.