Part 2: Emerging Trends of Thermal Flow Meters

Last week in the first part of my guest post, I shared some of the reasons why the Coriolis flow meter has cornered such a large part of the flowmeter measurement market. Accuracy is the main reason why this type of flowmeter has been so commonly used in industrial applications up to this point. But this week I’ll provide some interesting facts that might just change your mind about the effectiveness of thermal flowmeters.

Thermal flow meters are widely used for flare and stack gas measurement and for measuring the flow of industrial gases, and they also have a wide variety of applications associated with greenhouse gases. For flare and stack gas applications, the main competitors for thermal meters are differential pressure (DP) and ultrasonic flow meters. Coriolis meters don’t compete here due to the large line sizes involved, and also because Coriolis-style accuracy is generally not required for these applications.

In terms of developing more accurate meters, thermal flow meter suppliers are working to improve their technologies to enhance the accuracy of their meters. Sierra Instruments, for example, has developed the QuadraTherm thermal flowmeter to address the issues of accuracy and reliability. The QuadraTherm uses four temperature sensors instead of two, thereby better isolating gas mass flow rate also known as forced convection, which is the heat taken away from the velocity sensor by the flow stream.  The QuadraTherm measures only this heat and calculates out other heat transfers like stem conduction that can appear as flow, but aren’t.  All of this brings the flowmeter’s accuracy to 0.5 percent of reading when measuring above 50 percent of full scale flow. This approximates the accuracy of Coriolis meters for gas flow measurement.

Sierra Instruments was one of the original companies to introduce thermal flow meters to industrial markets in the mid-1970s. They have been working since that time to improve thermal technology, and to broaden their applications. It is not surprising, then, to see Sierra come out with a product that improves the accuracy of thermal flowmeters.

Jesse Yoder, Ph.D., is president of Flow Research Inc. in Wakefield, Mass., a company he founded in 1998. He has 25 years of experience as an analyst and writer in process control. He specializes in flow meters and other field devices, including pressure and temperature products.