Accurate measurement of the volumetric flow rate of working liquids is essential for process control, as well as energy consumption evaluation. Electromagnetic flowmeters have gained popularity in applications where low pressure drop and low maintenance are required. Dwyer Instruments, Inc., recently developed an insertion electromagnetic flowmeter (IEF) featuring accurate and reliable measurement of flow rate in the pipes. The working principle of an electromagnetic flowmeter is the well-known Faraday’s law of induction. According to the law, the velocity magnitude of the fluid perpendicularly passing through a magnetic field is proportional to the induced electric potential difference. For simplicity, all of the coefficients in the Maxwell–Faraday equation can be combined together into a configuration-based coefficient, which is commonly referred to as the *K*-factor. The value of *K*-factor for each type of electromagnetic flowmeters is often determined by the manufactures during the calibration process prior to the application. Once the value of *K*-factor is known, the relationship between the measured electric signal and the flow velocity is uniquely decided. However, an unexpected and non-repeatable behavior in the *K*-factor was observed during the calibration process and the non-repeatable behavior imposes challenges for precise measurement. On-site trouble-shooting is labor-intensive and time consuming and the detailed flow structure near the electrodes is unavailable to testing engineers to identify the cause of the problem.

As an alternative, a one-way coupled magnetohydrodynamics model was developed to reduce the effort and time of on-site trouble-shooting and optimization. By modeling the measurement process, the transition of the flow regions and the regeneration of the boundary layer in the vicinity of the electrode surface were identified as the major causes to the non-repeatable issue. A series of parametric studies were performed under different model configurations and operating conditions to provide guidance for future designs. The results show that both the measurement location and the length of the flow channel below the electrode are neither ineffective nor feasible to completely eliminate the non-repeatable decrease-to-recovery phenomenon of the *K*-factor. The third solution, however, successfully resolved this issue without causing too much additional effort in future production. The pair of electrodes were further embedded into the body of the IEF to smooth the transition between boundary layers. The CFD-aided new design showed great repeatability and completely eliminated the decrease-to-recovery phenomenon of the *K*-factor in the field test. The improvement in the IEF design was implemented in production in less than one week and it reduced the calibration time by 50%.


CFD Analysis and Improvement on an Insertion Electromagnetic Flowmeter

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Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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