# Flow Meter Selection Guide Part III: Flow Profiles and Reynolds Numbers

When it comes to flow meter selection, it is imperative to remember that every liquid of gas will behave differently when flowing through the pipeline due to its level of viscosity (level of resistance of flow) and each application will have different conditions that will effect flow. Because of this, no single flow meter will suite all jobs and conditions.So, how are you supposed to figure out which flow meter is best for your application?

Profiling your flow & calculating Reynolds numbers

Flow Profiles:

A flow profile refers to a vector diagram of the conditions within the pipe and how the fluid will respond to those conditions.

In short, this diagram will explain the behavior of your liquid as it flows through the pipe based on  viscosity (level of resistance to flow) and the velocity at which the fluid travels (affected by level of viscosity). Once you determine the level of viscosity and how the liquid will behave you can begin to narrow down your many options for flow meter selection.

So what kind of fluid do you have?

a-    Newtonian

b-    Non-Newtonian

Reynolds Numbers:

Do you have Laminar, transitional, or turbulent flow?

You figure this out by calculating the Reynolds Number. The Reynolds Number gives you a ratio of inertial forces to viscous forces, telling you the importance of each of these forces in your flow conditions. Depending on the profile of your liquid, this ratio will vary.

A Reynolds number, once calculated, can be interpreted as follows:

–        less than 2,000= Laminar

–       2,000-4,000= Transitional

–       4,000+ = Turbulent

This will help you narrow down your flow meter selection even further when you compare your options Reynolds range to the number you just calculated to help pick the one that is best able to meet the demands of the application.