Basic Theoretical Research On The Electromagnetic Flow Sensor With Harmonic Vector Field And Resistive Network Modeling Employed

In recent years, the worldwide shortage of water resources and the increasing demand have resulted in the optimal allocation of the limited resources, the energy conservation and the emission reduction, and the accurate measurement of the fluid is considered as one of the key problems to be solved. Among the leading sensors applied in flow measurement, the electromagnetic flow sensor is a kind of representative inductive sensor developed rapidly from the 1950 s, and it receives widespread attention and favor owing to the fact that it is mainly featured by high measurement precision, wide measurement range and insignificant effect of the flow field distribution in the pipe. Accordingly, the basic theoretical research on the electromagnetic flow sensor becomes one of the hotspots which have been concentrated on by domestic scholars, foreign scholars and technical workers for years, with a handful of related papers, patents and monographs presented continually. However, the further theoretical research on electromagnetic flow sensor, especially the exploration of the field theory and the sensor characteristics based on the multi-physics coupling, remains to be developed and improved, given that it is involved in the interdisciplinary research, including electromagnetism, fluid mechanics, information science, etc. Based on the background above, two core problems in the field of the electromagnetic flow sensor, covering the universal theoretical methodology for analyzing the weight field and the flow field, are mainly addressed in this dissertation, and the major work is listed as follows.Firstly, essential achievements in the past theoretical research and the existing problems in the field of the electromagnetic flow sensor are arranged and summarized. On one hand, the current research situation about the measurement methodology, the theory of the weight function and the theory of the flow field distribution in pipes is introduced, with the existing problems arranged and summarized. On the other hand, the basic principle and measurement equations of the electromagnetic flow sensor are presented and the classical theoretical achievements of the weight function and the fluid are introduced to pave the necessary way for the quotation later. The theory of partial differential equation and its calculation methodology is introduced for mathematical modeling and the building of the simulation platform, laying a solid foundation for the research itself.Secondly, the universal methodology for calculation of the weight function based on the harmonic vector field and resistive network modeling is investigated and presented. Three important vector fields in classical field theory and their related characteristics are introduced briefly, and the essential relationship between the fundamental equation of the harmonic vector field and the passive irrotational physics field is studied. The conception of the methodology for the equivalent simulation of the multi-physics field is addressed and introduced to the research on the weight function of the electromagnetic flow sensor. Considering that the weight vector field is a kind of the harmonic vector field in theory, the physical meaning of the weight function based on the field theory is discussed, with the equivalent definition and the simplified model obtained. Besides, two resistive networks based on different coordinate systems are provided to adapt to the electromagnetic flow sensor with different geometric structures. According to the research achievements above, the electric potential and current density of each point in the effective domain of the sensor space can be simply calculated by Kirchhoff’s current law, with the resistive network modeling of the fluid in pipes and the boundary of the sensor employed. Combined with the equivalent definition of the weight function, the corresponding distribution of the weight function can be further obtained. The methodology for calculation is verified by both theoretical analysis and numerical simulation for the purpose of the feasibility and the effectiveness, providing the guarantee for the implementation of subsequent cases and the related analysis on the characteristics of the sensor.Thirdly, the weight function and its characteristics of three electromagnetic flow sensors with representative structure are investigated by means of the methodology for calculation of the weight function based on the harmonic vector field and resistive network modeling. The classification of electromagnetic flow sensor is introduced and three kinds of electromagnetic flow sensors in partially filled pipes which can reflect not only the problems about the mixed boundary condition differentiated from those in the classical model, but also the blank in theory and value in engineering are selected as the examples. The weight function of the sensors in the uniform magnetic field and the characteristic relationship among various physical parameters are studied theoretically, verifying the feasibility and the effectiveness of the methodology for calculation of the weight function based on the harmonic vector field and resistive network modeling by the examples.Fourthly, the theoretical problem about the flow field distribution of the steady stream in partially filled pipes are studied, with a simplified model of the steady stream in partially filled pipes based on N-S equations presented. According to the actual situation, the premise of the research on the steady stream in partially filled pipes is given, and the mathematical model based on N-S equations is made, with the equations of mathematical physics and the boundary conditions determined, considering that the steady stream in partially filled pipes is similar with that in open channels and the two-phrase flow. The flow field is calculated by the methodology combined with the mathematical model and the numerical simulation. The correctness and effectiveness of this model are verified by means of the comparison with the measured data of the flow field in the literature. Based on the model and the platform of the numerical simulation, the flow field distribution along pipes, the flow state, the characteristics of the flow distribution and the distribution of the flow velocity in cross sections with the various fullness degree of the fluid are investigated, and several achievements are obtained, including the suitable range of the length of the straight pipe upstream from the sensor which can form the fully developed flow, the characteristic relationship between the normalized velocity and fullness degree of the fluid, isolines of the velocity in two-dimensional cross sections and three-dimensional curved surfaces of the partially filled pipes, paving the way for the subsequent theoretical design and the experimental verification of the sensor.Fifthly, the verification platform, including the hardware, the software and the electromagnetic flow sensor based on long-arc electrodes in partially filled pipes is selected and established. The basic design concept of the electromagnetic flow sensor in partially filled pipes is discussed, and a kind of structure design for the electromagnetic flow sensor based on long-arc electrodes in partially filled pipes is analyzed and chosen in view of two aspects which are the velocity measurement and the liquid level measurement. Starting with the basic requirement of the converter, the hardware system which is composed of the excitation module, the module of analog signal processing, the module of microprocessor control and the module of human-computer interaction is designed, with the key modules analyzed and discussed in detail. The overall content of the software design is determined, the foreground-background system is designed and applied in the software architecture of the electromagnetic flow measurement system in partially filled pipes. Combined with the characteristics of dual-CPU parallel mechanism, the corresponding programs for the host computer and the slave computer are developed, and the timing of the dual excitation and the methodology for calculation of the fluid information, including the velocity, the value of the zero point, and the liquid level, are investigated in the electromagnetic flow measurement system in partially filled pipes, with the algorithm of the digital filter based on the mode presented to tackle the actual problem of the signal denoising. The reliability of the system above is verified by both the calibration of the real flow with the prototype and the detection result of relevant departments.Sixthly, the experiment for verification and the related analysis on characteristics in view of the basic theoretical research on the electromagnetic sensor with harmonic vector field and resistive network modeling employed are made. Based on the platform of the verification system, the experimental device and the brief working process applied in the measurement of the flow in partially filled pipes are designed and introduced, and the major design concept of the experiment for verification is discussed, with the flow velocity and the sensitivity of the sensor selected and employed to verify the theoretical model addressed in this dissertation. Through the comparison of theoretical model and the data obtained from the real flow experiment, the correctness and the reliability of the theoretical methodology presented in this dissertation are verified macroscopically, whereas the related characteristic curves of the electromagnetic flow sensor in partially filled pipes and the influences of parameters are given based on theoretical models, which provide the reference for the practical application and the related basic research in future.