Measurement of wastewater by non-full-pipe electromagnetic flowmeters

　　A non-full pipe refers to a condition where the fluid does not fill the pipe cross section. Since the liquid level of the fluid changes instantaneously under the non-full pipe condition, it is difficult to accurately measure the liquid level value of the fluid in the pipe. Electromagnetic flowmeters are generally used to measure the flow of non-full sewage because of their corrosion resistance, high measurement accuracy, and small flow field distribution in the pipe. However, since their measuring electrodes must be immersed in the fluid to obtain the measurement signal, it is difficult to collect the measurement signal when the fluid level is lower than 0.1D (10% of the pipe diameter). In addition, there are multiple pairs of electrodes in the flowmeter. Once a problem occurs in one of the electrodes, the entire flowmeter needs to be replaced, which increases the cost.

　　In order to solve the problem of difficult flow measurement when the fluid level is lower than 0.1D, this paper proposes a new non-full pipe flow measurement method: based on the connecting pipe principle, the fluid level value is measured by a high-precision pressure sensor, and the accurate flow value flowing through the measured pipeline is obtained after processing by the level-flow function model. Before the experiment, a U-shaped connecting pipe is connected to the appropriate position of the measured pipeline, and the flow state of the gas-liquid two-phase flow in the pipeline is simulated based on the computer fluid dynamics (CFD) simulation technology to obtain the diameter size and the optimal installation position of the U-shaped connecting pipe.

　　100mm was selected as the measured pipe diameter. According to the simulation results, the diameter of the U-shaped connecting pipe should be 0.02m, and the installation position of the connecting pipe should be selected at a distance of 1m to 2.5m from the water inlet. The experimental platform was built based on the simulation results, and the liquid level-flow model was initially established based on the hydraulic method, and the model was calibrated through experiments. The flow results output by the system were compared with the measurement results of the electromagnetic flowmeter. The results show that under the condition of ensuring smooth pipeline, when the liquid level height of the fluid is not higher than 10% of the pipe diameter, the measurement error is <2%, and the repeatability error is 1.45%, which verifies the reliability of the measurement method.

　　The measurement method proposed in this paper breaks through the limitation that the traditional non-full pipe flowmeter is difficult to measure the fluid flow with a liquid level height below 0.1D, and avoids the problem of large loss, low accuracy and severe wear caused by the built-in liquid level meter. The liquid level measurement device is placed outside in the U-shaped tube, which is easy to install and maintain. It greatly reduces the cost and has certain significance for the research on non-full pipe sewage flow measurement.

　　The above is the "Explanation of the measurement of sewage by electromagnetic flowmeter with a non-full pipe" shared by the electromagnetic flowmeter manufacturer. Thank you for watching. If you have any questions, you can consult online or leave us a message. We will answer you wholeheartedly.