How to select the right flow meter for your application?

Man with glasses and yellow jacket selecting the Right Flow Meter IN-FLOW

Selecting the right flow meter is the key to success while selecting the wrong one means nothing but trouble. There are a lot of flow meters to choose from for every kind of application.
The right flow meter is essential for crucial data collection and the wrong one can lead to grief in the budget and costly lost production time. In this blog I will discuss some of the important elements that go into the decision-making process of a flow meter, taking into account the differences between volume- and mass flow measurement. Read below how you can more easily select a flow meter for your application.

Price versus popularity, of a flow meter

The most common criteria to select a flow meter are: price and popularity. Beware of relying on two of the most common criteria that people tend to use in the selection process: cost and popularity. If you place price at the top of your criteria, it will be easy to get the wrong flow meter for the application or one that does not hold up physically or performance-wise. That bargain will quickly turn into a budget nightmare.

A Set-up of Coriolis Mass Flow Meters (mini CORI-FLOW)

If the measuring device and its ancillary equipment need frequent and expensive maintenance, what you saved on that flow meter will quickly dissipate. Moreover, a flow meter that has a higher initial investment can also make up for it by costing less to maintain and operate. Coriolis mass flow meters are more expensive in purchase initially than many other types of flow meters, but can save a great deal of money over time because they are easier to maintain, translating into less downtime.

While it is important to research what type of flow meter is most commonly used in your industry, just selecting what is popular can also lead to disaster. If the flow meter is not appropriate for the application, measurements can be under or over which means valuable material can be lost and revenue negatively impacted.

Ultrasonic volume flow meter (ES-FLOW)

Ultrasonic volume flow meters

Advances in technology can also put instruments on the market that may not be as well-known, but provide a better solution. For instance, in the past, inline ultrasound flow meters had to be re-calibrated when a new fluid was introduced and could not be used in applications where hygiene was important. Nowadays new ultrasonic flow meters have solved those concerns and opened up the use of inline ultrasound flow meters to those types of applications.

A flow meter is a highly technical device that is influenced by lots of variables. We’ll breakout the most important ones, but realize that every application is unique.

Volume or Mass flow measurement

There are two basic measurements of fluids, volume and mass flow measurement, so a flow meter is either a volumetric flow meter or a mass flow meter. However, you can calculate volume from mass and mass from volume if you know the density and agreed upon variables. Whether a volumetric flow meter or mass flow meter is the best depends on the application, its components and the purpose of the measurement.
Want to know more about volume vs mass flow and why mass flow reference conditions matter?

picture showing volume flow and mass flow

Volume flow versus Mass flow for selecting right flow meter

Flow meter categories based on fluid

Some flow meters can be easily eliminated because they simply will not work with the application. For instance, electromagnetic flow meters will not work with hydrocarbons and require a conductive liquid to function. Many flow meters cannot measure gases or slurries. Listed below are some of the main flow meter categories paired with the fluid type the meters can handle.

Gas – Coriolis Mass, Thermal Mass, Ultrasonic, Variable Area, Variable Differential Pressure, Positive Displacement, Turbine
Liquid – Coriolis Mass, Thermal Mass, Ultrasonic, Variable Differential Pressure, Positive Displacement, Turbine, Electromagnetic
Slurry – Coriolis Mass, some subsets of Variable Differential Pressure, Electromagnetic, Ultrasonic
Vapour – Vortex, Ultrasonic, Diaphragm, Floating Element

Fluid properties

It is crucial to know the properties of the fluid being measured, below are some of the primary components:

Type of fluid – liquid, gas, slurry, vapour
Density
Viscosity
Temperature
Pressure
Condition of the fluid – foreign objects in it, suspended particles, air bubbles,
Other contaminants
Flow consistency – consistent or breaks, fill the pipe or partially fill or varies
Flow range – the minimum and maximum of the flow
Corrosive nature of the material – corrosive liquid or gas can deteriorate inline sensors

Physical properties

It is also important to know about the physical dynamics of the application site. Some of the physical properties of the site to consider are:

Configuration of the pipe before and after the flow meter and the length of straight pipe at the inlet and outlet of the flow meter.
The size of the pipe. Some flow meters have a poor performance with very small pipes and some cannot measure fluids in larger pipes
The material the pipe is made from
The surrounding environment and whether it is stable or variable
Will the flow meter work at a certain angle? This can seriously affect a flow meter’s performance

Read in our previous blog why the choice of piping is important for thermal mass flow meters

multiple pips for Bronkhorst thermal mass flow meters

Piping in flow meters

Flow meter specifications

Last but not least, also the specifications itself have to be taken into consideration when selecting the right flow meter.

Accuracy – Naturally, an important factor of a flow meter is accuracy. To even suggest that accuracy is a variable seems ridiculous. Who would want an inaccurate meter? However, not all flow meters possess the same accuracy; some applications do not even require precision.

Repeatability – Repeatability means the number of times (%) you get the same results running the same test or measurement under the same conditions. Accuracy requires repeatability, but repeatability does not require accuracy. It just needs consistency. Therefore, it can be said that repeatability of a flow meter is often considered even more important than accuracy.

Turndown Ratio or Rangeability – This implies the range that a flow meter can accurately measure the fluid. Usually, it’s best to choose a flow meter with the greatest range available without compromising other components that are more critical.

Hygiene requirements – Flow meters for food, pharmaceuticals, and the medical industry especially demand sterile environments.

Cost – As stated above, this should include installation, maintenance and repairs over time. How much the meter costs to operate, like its electrical demands, can also increase the overall cost of the flow meter.

As you can see, there are a lot of variables to finding the right flow meter and the ones we have listed are only the basics. This does not even touch on the various options in different models. The best way to get the right meter is to get help with your search and team up with experts in the field. Experience matters.

It is important to get your information from people who know these complex and important devices. To let Bronkhorst help in the search for the right flow meter for your needs, please contact us.

When you have selected the right flow meter, the next step is installing this instrument. Graham Todd gives some useful tips when installing a mass flow meter.

How to select the right flow meter for your application?

Price versus popularity, of a flow meter

Ultrasonic volume flow meters

Volume or Mass flow measurement

Flow meter categories based on fluid

Fluid properties

Physical properties

Flow meter specifications

Would you like more information about mass flow meters?

Why is the choice of piping important for thermal mass flow meters?

Mass Flow Instruments, Top 10 tips for installation

Blog series: How to handle low liquid flows? Part 5