Fundamental Research On The New Type Multi-electrode Insertion Electromagnetic Flow Sensor

Traditional electromagnetic flowmeters have significant limitations for meas-uring the flow of large diameter pipelines, while the insertion electromagnetic flowmeter is becoming increasingly popular among users for the same usage with its hightlighting advantages of low price, small weight, easy disassembly and repair as well as good versatility. What's more, one specification may be used in pipelines of various diameters. However, this kind of flowmeter has its own disadvantages, namely, it's not only deeply affected by the fluid flow characteristics, but also need to have a longer length of straight pipe at the application scene. Therefore, develop-ing the key technology which improves the performance of insertion electromag-netic flowmeter has been an important subject in flow measurement.This dissertation mainly focuses on the basic study of insertion electromagnetic flow sensor with multi-electrode measurement. Insertion electromagnetic flow sen-sor is based on the electromagnetic induction and the fluid velocity distribution of measuring the flow field. And the distribution of weighting function and electro-magnetism field and flow field play a key role in affecting its measurement result. Thus, the research of insertion electromagnetic flow sensor must be carried out in the three perspectives which are the flow field, the electromagnetic field and the weight function. At present, the development of the finite element technique and CFD (Computational Fluid Dynamics) has provided the brand-new way for the re-search on insertion electromagnetic flow sensor, and has also expanded the new space and the new method for it. The method of CFD is used to study physical model of the sensor geometry, and the numerical simulation is employed to analyze the relevant effects of the flow field change upon the sensor. The characteristics of three special regions of high flow velocity around the sensor staff are summarized. To remove the effects of the flow field change upon the sensor, the feasible design of new Multi-electrode insertion electromagnetic flow sensor is proposed. Adopting technology of the Multi-electrode multi-point measurement, a new way to solve the problem of sensor which is deeply affected by the flow field is provided.This dissertation is carried out around the study of key technologies of the new type sensor. First of all, a summary of the theoretic basis related to the insertion electromagnetic flowmeter and the research methodology are introduced. The basic measurement equation and weighting function of existing insertion electromagnetic flow sensor are analyzed. The empirical models of flow field distribution like tradi-tional Nikuradse model and the measurement model of existing insertion electro-magnetic flowmeter are also analyzed. Based on the finite element method of Max-well equations, the electromagnetic field models of insertion electromagnetic flow-meter and the analysis tools and research methods are introduced. The CFD-based numerical simulation methods of flow field are introduced in detail. The governing equation such as Navier-Stokes (N-S) equation, the Reynolds time-averaged equa-tions and its standard k-εmodel, the Large eddy simulation (LES) method, the wall function and near wall model are analyzed in detail. And the methods of the com-monly used solution to the governing equation are discussed.Secondly, this thesis tries to study the four aspects as follows: the parallel computing platform of CFD, the pipeline flow field distribution simulation, the flow around a bluff body simulation and the insertion electromagnetism flow sensor's flow field simulation. Based on the research of parallel computing environment, the very excellent parallel computing cluster systems has been built, and the basic per-formance of the parallel computing platform is tested. Based on the CFD turbulent model, the simulation of flow field distribution gives out the velocity profile of pipeline, which is in line with the velocity profile of traditional Nikuradse model perfectly and closer to actual flow field. The Simulations of flow around bluff body show us the cylindrical shape, the trapezoidal body along with the detailed process and the occurrence mechanism which vortex produced and were shedding. The vor-tex production essence of flow around bluff body and the research methods of measurement flow are identified. The measurement methods are discussed from the angle of the simulation of flow field and the influence of cylindrical probe head to the flow field. And then, this dissertation proposes the plan of multi-electrode meas-uring flow velocity and the disturbance of flow. This dissertation also gives out the three characteristic regions of flow velocity around the sensor staff.Then, the dissertation analyzes the measurement principles from the perspec-tive of the flow field distribution. The improved measuring methods of the multi-insertion electromagnetic flowmeter and the multi-electrode radial tachometer type insertion electromagnetic flowmeter are discussed. The measurement principle and solution of multi-parameter and multi-electrode insertion electromagnetism flow sensor are proposed. The study gives the structural design of the sensor and its model study. And the spatial relations among electrode, flow field and magnetic field are established. And the principle of multi-electrodes measuring is given out. The measurement equation of sensor multi-point measuring is presented. Base on the matlab PDE tool's finite element method analysis, the weighting function of electromagnetic flowmeter sensor and insertion electromagnetic sensor are simu-lated and analyzed. The work magnetic field of insertion electromagnetic sensor are also simulated and analyzed. The research discusses the weighting function and the magnetic field design of the multi-electrode insertion electromagnetic flow sensor. Theoretically, the design method is determined for designing the most superior work magnetic field of insertion electromagnetic flow sensor.Finally, in order to verify the feasibility and practicality of the design, a multi-electrode insertion electromagnetic flow sensor and a signal converter system have been manufactured, and the corresponding experiment pipeline test system has also been set up. Based on this, the experiments on the spatial relations measuring with multi-electrode are carried out, and the results of test data are analyzed. The results confirm that the signal of multi-electrode sensor has linear relationship with the flow rate, and the signal characteristics of three pairs of electrodes are true re-flection of the changes of the three flow rate characteristic regions. The results also confirmed the measurability of multi-electrode sensor which measures the data of flow field distribution and the signal of flow around. All of these provide the basis to reduce the influence of flow field distribution in the sensor measuring finally, and to improve the insertion electromagnetic flowmeter's performance.