Velocity-Profile Deviations Influence Flowmeter Performance

Selecting the right flowmeter for the liquid
By Corte Swearingen
Reprinted from Chemical Processing magazine 

Close your eyes and imagine a world in which all fluids flowing down pipes are perfectly homogeneous, having no disturbances or eddies in the flow stream. A world in which pipes always contain fully developed turbulent flow and pipe bends and obstructions are non-existent.

Sounds silly right? But these are the hypothetical conditions upon which flowmeter accuracies are based. If deviations from these conditions exist, accuracy and/or repeatability will degrade. This article will discuss the first of four major influence quantities that affect flowmeter accuracy and performance: velocity-profile deviations, non-homogenous flow, pulsating flow, and cavitation. With this background, we will then look at how these influence quantities factor into flowmeter performance and what can be done to minimize their effect.

Imagine a horizontal pipe a few feet in front of you at about eye level. If a vertical cut were made through the center of the pipe to remove the front half of the pipe, it would be easy to see how "nicely behaved" fluid flow develops.