Vortex Shedding and Fluidic Flowmeter Applications
(Part 2 of 4)

E-Zine February 2009

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Vortex shedding and fluidic flowmeters can be used to measure the mass flow of gases and vapors. These flowmeters measure the fluid velocity that is used to infer the mass flow in conjunction with other measurements, such as pressure and temperature. Because the density of gases and vapors is usually significantly lower than that of liquids, the ability to generate sufficient hydraulic energy to operate the sensing system can be limited. Therefore, vortex shedding and fluidic flowmeters in gas and vapor applications generally have higher turn off velocities, so they may not measure when the flowing stream is at low velocity, at low pressure, or at high temperature.

Vortex shedding and fluidic flowmeters measure the velocity of the fluid. The measurement is linear with velocity and can exhibit a large turndown when high fluid velocity is acceptable.

Variation in certain characteristics of vortex shedding and fluidic flowmeters has allowed this technology to be applied to many processes. The following sections define flowmeter design categories and how they fit the needs of their intended applications.

Liquid Vortex Shedding and Fluidic Flowmeters
Most vortex shedding and fluidic flowmeters measure liquid flows, however some designs were developed specifically and exclusively for gas flow measurement.

Gas Vortex Shedding and Fluidic Flowmeters
Although the majority of vortex shedding and fluidic flowmeters were designed to measure liquid flow, many can be applied to measure the flow of gases. Vortex shedding and fluidic flowmeters measure gas velocity, so pressure and temperature compensation may be necessary to accurately infer mass flow measurement. Because temperature and pressure can vary significantly in actual operation, failure to compensate vortex shedding and fluidic flowmeter measurements can introduce significant measurement errors in many applications.

Steam Vortex Shedding and Fluidic Flowmeters
Some vortex shedding and fluidic flowmeters can be used to measure steam flow. These flowmeters are designed for gas (vapor) flows at high temperatures. The temperature ratings of these flowmeters must exceed the operating steam temperature (taking superheat into account) to avoid damaging the flowmeter. The temperature ratings of practical designs vary from approximately 250°C to over 400°C.

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Excerpted from Excerpted from The Consumer Guide to Vortex Shedding and Fluidic Flowmeters

ISSN 1538-5280