Editor’s Note: This is Part III in a five-part series discussing the types of technologies that can be applied to measure the flow of raw materials.
Positive displacement flowmeters that measure the actual volume of the fluid passing through the flowmeter (volumetric flow) and flowmeters that measure fluid velocity were discussed in previous articles (May and June 2015). These technologies measure and infer (respectfully) the volume of the fluid passing through the flowmeter. However, the amount of the fluid contained in a given volume passing through the flowmeter can vary with fluid density where the fluid density is dependent upon the fluid pressure, temperature and/or composition. Gas applications can pose significant measurement challenges due to significant density changes that can occur in many applications.
Mass flowmeters can be used to measure the mass of the fluid passing through the flowmeter. Coriolis mass flowmeters use the properties of mass to measure mass flow while thermal flowmeters utilize the thermal properties of the fluid to measure mass flow. Positive displacement and velocity flowmeters that measure and infer volumetric flow can be used to infer mass flow by multiplying the volumetric flow by the fluid density.
However, in many applications (especially gases), the desired measurement is the amount of fluid passing though the flowmeter that can be commonly described as a mass — not as a volume. Stated differently, the commonly desired measurement is the mass flow of the fluid — not its measured or inferred volume.
It would be logical to presume that mass flowmeters should be utilized in most flow measurement installations. However, cost constraints, process conditions, accuracy requirements, and relatively small operating density variations in many applications (especially liquids) allow flowmeters other than mass flowmeters to be successfully applied in most flow measurement applications.
To be continued.
David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes, LLC, offering engineering, training, strategic marketing consulting, distribution consulting, and expert witness services for manufacturing and automation companies. Spitzer and Boyes is also the publisher of the Industrial Automation INSIDER. Mr. Spitzer has more than 40 years of experience and has written more than 10 books and 300 articles about flow measurement, instrumentation and process control. David can be reached at +1.845.623.1830 or via www.spitzerandboyes.com. Click on the "Products" tab to find his Consumer Guides to various flow and level measurement technologies.