Practical application of electromagnetic flowmeter in lead-bismuth alloy flow measurement

One thing that comes to mind about electromagnetic flowmeters is to measure sewage treatment, but in this article, we will talk about the practical application of electromagnetic flowmeters in lead-bismuth alloy flow measurement, let us continue to analyze:

  The electromagnetic flowmeter adopts the Faraday electromagnetic induction principle, and uses magnets to form a uniform and stable magnetic field B on both sides of the pipeline, and passes through the inside of the pipeline, and the magnetic field is evenly distributed in the pipeline. During the flow of the lead-bismuth fluid, the magnetic induction line is cut, and the induced potential E is generated. The induced potential is proportional to the flow rate, and the flow measurement of the lead-bismuth alloy in the pipe can be realized by parameters such as the inner diameter d of the pipe and the magnetic field strength B. Electromagnetic flowmeters are divided into DC electromagnetic flowmeters and AC electromagnetic flowmeters according to different excitation methods.

  1. DC electromagnetic flowmeter

  The direction of the magnetic field of the DC electromagnetic flowmeter remains unchanged, and a permanent magnet is usually used as the magnetic field source. According to the measuring principle, the DC electromagnetic flowmeter consists of two systems. The magnetic circuit system generates a magnetic field, and the signal acquisition system collects the signal. Therefore, the flowmeter is simple in structure, strong in signal stability and less affected by the flow characteristics of lead-bismuth fluid, and has become the main method of lead-bismuth flow measurement in the world. CHEOPE and LECOR circuits in Italy, LIsor circuits in Sweden and THESYS circuits in Germany all use permanent magnet electromagnetic flowmeters to detect flow.

  When ENEA studied the measurement of metal fluids by electromagnetic flowmeters, it was found that the flow measurement accuracy was affected by the wetting performance of boundary conditions, resulting in unstable flow state of lead-bismuth alloys and uneven flow velocity distribution in the cross-section, which was not conducive to the detection of average flow velocity. In the process of using the flowmeter, in order to ensure the measurement accuracy, it needs to be calibrated regularly. At the same time, ENEA also found in the flow measurement of the LECOR loop that a non-conductive oxide layer is formed in the tube wall of the electromagnetic flowmeter. With the gradual growth and expansion of the oxide layer, the measurement accuracy of the flowmeter gradually decreases until it fails completely. However, the flowmeter at the cold end can keep running because the operating temperature of the cold end flowmeter is lower, the growth of the oxide layer is relatively slow, and the diameter of the pipe is relatively large, and it takes longer for the oxide layer to cover the surface of the pipe. So keep running.

  The signal acquisition method of electromagnetic flowmeter determines that the signal transmission channel composed of lead-bismuth fluid, pipeline and electrode has high conductivity. The corrosion product produced by corrosion is an insulating oxide layer, which can hinder or even cut off the output of the potential signal, and eventually make the flowmeter lose its measurement function.

  2. AC electromagnetic flowmeter

  The difference between the AC type electromagnetic flowmeter and the DC type is the excitation method, which uses alternating current to energize the coil. The magnetic field inside the coil is in a dynamic transformation process, and the direction of the magnetic field also changes with the direction of the current. The measurement method is different from the DC measurement of the induced potential signal. The metal fluid generates an induced magnetic field in the alternating electric field. The induced magnetic field is proportional to the flow rate in the case of a first-order approximation. Compared with the DC type, the biggest advantage is that it does not require a sensor with high time resolution to achieve accurate flow measurement. However, due to the characteristics of signal transmission, an insulating layer is required between the sensor and the fluid to prevent the signal from being shunted and affecting the test accuracy. Therefore, there are extremely high requirements for the compatibility of flowmeter structural materials.

  KIT in Germany installed a non-contact phase-change electromagnetic flowmeter in its test device. The metal fluid passes through two alternating excitation coils to generate two induced magnetic fields with a phase difference. Using the proportional relationship between the phase difference of the induced magnetic field and the flow rate, the detection of the fluid in the pipe is realized. After testing in the gallium indium arsenic circuit and the sodium circuit, it was found that when the magnetic Reynolds number of the gallium indium arsenide exceeds 0.1 and the Reynolds number of the sodium circuit exceeds 0.35, the linear relationship between the flow rate and the phase difference is lost. The effect resulted in a final flowmeter measurement error of 5%.

  The outstanding features of electromagnetic flowmeter are simple structure and stable output signal. However, due to the oxidation of the lead-bismuth alloy on the pipeline, the signal output will decay with time, and the change of temperature will cause the conductivity of each metal part of the sensor to change and the inner diameter of the measuring tube to change. Therefore, the flowmeter needs to be periodically calibrated to correct the temperature. and oxidation bring errors.

  Are the connection methods of the above two electromagnetic flowmeters, the scene used and the magnetic field helpful to you? If you want to know more about the flow meter, please feel free to inquire