Volumetric flow rate or mass flow rate?

As with most flowmeter selection processes the choice of volumetric or mass is decided by just a couple of criteria. Here’s how:

The first step is defining the fluid type i.e. liquid, gas, steam etc. Once you’ve decided your application is liquid, the next most important criteria is cost.

Ritter Gas Flow Meter | Litre MeterWhilst it’s true that some processes require an input of mass rather than volume the cost implication can alter your automatic selection. For example, most fermentation reactors require an input of mass.

However, if the measurement of volume is very cheap and the pressure and temperature and gas composition are known then the mass can be calculated very easily. On the other hand, if you require a certain degree of accuracy a thermal mass gas flowmeter may be the best selection.

This pragmatic approach derived from just a few parameters not only illustrates why volume and mass measurement can be interchanged but also how consulting the specialists is an important move.

What does volumetric flow get you?

Generally speaking it’s a readout or output in litres, cc or gallons rather than pounds or kilogrammes.  Most flowmeter technologies infer or measure volume

and require no post-processing to provide a volumetric total or flow rate. A typical technology is positive displacement which actually provides a pulse for each known volume.

An electromagnetic meter calculates a volume by knowing the cross-sectional area of the measurement tube and measuring the velocity.

A turbine meter compares a frequency output from it’s sensor to a calibration certificate and so on. The measurement is neither worse nor better than a mass flowmeter. That depends on many other variables. The viscosity, pressure and temperature of the fluid may influence the choice of meter but either type could be suitable.

Volume Flow Meters vs Mass Flow Meters

Volume Mass
Positive Displacement Thermal Flow Meters
Differential Pressure Coriolis
Electromagnetic Angular Momentum Type
Orifice Plate
Pitot Tube
Turbine
Laminar Flow
Vortex Shedding
Ultrasonic
Venturi
Sonic Nozzles (with regulated pressure becoming mass meters)

Our own range of articles, source material:

Next Generation Flowmeters for Fluid Measurement and Control Solutions
Next generation flowmeters for Oil and Gas
Flowmeter Selection Strategies
The Calibration of Flowmeters
Considering the Pros & Cons of Volumetric Flow Measurement
When Do You Measure Mass Flow?

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