Capacitance Value Calculation And Structure Optimization Of Sensor In The Oil-air Lubrication ECT System

With the wide application of oil-air lubrication technology in high speed precision industrial equipment,higher requirements are put forward for the monitoring of various parameters of lubricating pipelines.In this thesis,capacitance tomography is used to monitor the parameters of multiphase fluids in small-diameter oil-gas lubrication pipelines.The key technologies involved in the imaging system are emphatically studied.The main contents and conclusions are as follows,(1)Two-dimensional mathematical model of capacitance sensor in ECT system,which is used in the oil-air lubricating system of small pipe diameter is built,the edge capacitance influence coefficient is defined,the relation of the edge capacitance influence coefficient and the pipe radius is studied in this thesis.The results show that the edge of capacitance influence coefficient in small pipe diameter is more than 0.5,and the edge capacitance influence coefficient declines with the pipe diameter increasing,the edge capacitance of the sensor has a great effect on the spatial graphic imaging error of ECT in the oil-air lubricating system.(2)The two-dimensional physical model of capacitance sensor is established;the finite element model is simulated by COMSOL software.The formula of relative permittivity is deduced according to the calculation expression of capacitance value.The simulation is carried out by changing the factors affecting relative permittivity Verification,spatial image reconstruction error as an evaluation index,the effects of relative dielectric constant on the edge capacitance are analyzed.The results show that the finite element model and the physical model of the sensor are real and effective;the ratio of the tube wall thickness,the oil film thickness and the gas thickness have distinct effects on the edge of capacitance value;the expression of permittivity at the derivation is validated both in calculation and simulation.This study provides a reference for the optimization calculation of capacitive tomography sensor.(3)A three-dimensional model of capacitance sensor in oil-air lubrication ECT system is built.The COMSOL software is used as the finite element simulation platform and the end surface of the lubrication pipe(annular flow)is the data acquisition area.The capacitance between the plates and the electric field vector value of the pixel are obtained.Based on the two-dimensional potential solution to the sensitive field,an expression based on the electric field for calculating the sensitivity value of a single pixel in space is deduced.The axial protection structure of the sensor is optimized by taking the structure optimization function as the optimization basis,Design-expert software as a platform for data processing and analysis,and the spatial image error as the structural optimization verification index.The results show that the length and spacing of axial guard ring can effectively improve the accuracy of the capacitance value and the sensitivity of the field uniformity,the calculation expression based on electric field allows a quick calculation of the sensitivity matrix,and adopting the sensor with additional axial protection plate to simulate the experiment,the image reconstruction quality is improved nearly 52.9%when compared with the reference sensor.