David W. Spitzer

Which of the following constraints are likely violated by a typical two-inch vortex shedding flowmeter application flowing water at 10-100 gallons per minute?

A. Flowmeter size

B. Reynolds number

C. Minimum flow

D. Minimum linear flow

E. Maximum flow

Commentary
The fluid velocities and Reynolds numbers at 10-100 gallons per minute are approximately 0.95-9.5 feet per second and 15,800-158,000 respectively.

Most suppliers offer a two-inch flowmeter (Answer A), so flowmeter size is not a problem. The maximum velocity (Answer E) is well within the constraints of most vortex-shedding flowmeters.

In this application, Reynolds number will vary from approximately 15,800 to 158,000. Operating at a Reynolds number as low as 15,800 (Answer B) may cause some vortex-shedding flowmeters to operate non-linearly (Answer D). However, operating at 0.95 feet per second (Answer C) will likely cause the typical vortex-shedding flowmeter to turn off and measure zero flow.
It should be noted that the velocity and Reynolds number constraints are interrelated. The flowrate directly affects the fluid velocity and its operating Reynolds number – both of which are constraints that must be satisfied for the vortex-shedding flowmeter to operate properly.