Which of the following flowmeter technologies can be applied to measure the flow of air in a round pipe?

A. Coriolis mass
B. Differential pressure
C. Magnetic
D. Thermal
E. Vortex shedding

Magnetic flowmeters only measure the flow of liquids, so Answer C is not correct. The remaining technologies can be applied to measure the flow of air. Thermal flowmeters and some differential pressure flowmeters can measure air flow under most commonly encountered operating conditions. Coriolis mass and vortex shedding flowmeters can also measure the flow of air under some operating conditions. Answers A, B, D and E are correct.

Additional complicating factors

Vortex shedding flowmeters turn off when the Reynolds number and air velocity are below their respective operating constraints. In addition, vortex flowmeters will turn off when the air density is not sufficiently high to operate the sensing system. The pressure drop across Coriolis mass flowmeters in air service can become excessive unless the air pressure is sufficiently high.

Just because a flowmeter technology can measure the flow of air does not mean that the technology will measure the flow of air.

David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes LLC, which offers engineering, seminars, strategic, marketing consulting, distribution consulting and expert witness services for manufacturing and automation companies. Spitzer and Boyes is also the publisher of the Industrial Automation INSIDER. He has more than 40 years of experience and has written more than 10 books and 350 articles about flow measurement, instrumentation and process control.

Spitzer may be reached at 845-623-1830 or via spitzerandboyes.com. Click on the “Products” tab to find his Consumer Guides to various flow and level measurement technologies.