Which of the following flowmeters could be used to measure 10 to 100 gallons per minute (gpm) of liquid with a specific gravity of 1.20 and a viscosity of 500 centipoise (cP) in a 3-inch pipe?

A. Coriolis mass 

B. Differential pressure 

C. Magnetic 

D. Positive displacement

E. Thermal 

F. Turbine

G. Vortex shedding


Thermal flowmeters are not applicable because they are used in gas service (Answer E). Reynolds number at maximum flow can be calculated as 3160 x 100 x 1.2 / 500 x 3, or approximately 250. Operation in the laminar flow regime with Reynolds numbers of 25 to 250 generally precludes the use of differential pressure (Answer B), turbine (Answer F) and vortex shedding (Answer G) flowmeter technologies. Coriolis mass (Answer A), magnetic (Answer C) and positive displacement (Answer D) flowmeters remain as potential technologies to apply in this application. 

Additional complicating factors

Many liquids with high viscosities, such as hydrocarbons, are not conductive, so magnetic flowmeters (Answer C) can sometimes be eliminated from consideration, simplifying the selection process.


David W. Spitzer


David W. Spitzer is a regular contributor to Flow Control  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 400 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.