Analysis And Optimization Of Characteristic Parameters Of Oil-air Lubrication ECT Sensor

The electrical capacitance tomography(ECT)sensor of an oil-air lubrication system is the first step to achieve the real-time monitoring of various parameters of the oil-gas two-phase flow in the lubrication process.Aiming at the characteristics of small pipe diameter,less oil and more gas,and thin oil film which the oil-air lubrication system has,the characteristic parameters of ECT sensor in the oil-air-lubrication system are studied and optimized in this thesis and the research main contents are as follows,(1)A three-dimensional physical model of ECT sensor which can detect the annular flow for an oil-air lubrication system is established,and its mathematical model considering the capacitance of the pipeline is got in this thesis.And then the influence coefficient of the pipeline capacitance is defined,and the impacts of the thickness and the radius of the pipeline on the measured capacitance are analyzed.On this basis,the image of the annular flow is reconstructed using LBP algorithm considering the pipeline capacitance,and the quality of reconstructed image is evaluated finally.The research results show that the influence of pipeline capacitance on the measured capacitance can be represented by the influence coefficient of the pipeline capacitance,the effect of the pipe capacitance on the measured capacitance will increase while the thickness increases or the radius of the pipeline reduces,especially the pipeline capacitance has a greater impact on the measured capacitance for small diameter pipes in an oil-air lubrication system.The spatial image error is reduced by 5.19% on average when the pipeline capacitance value is taken into account in the algorithm.(2)Three-dimensional physical models of oil-air lubricated ECT sensors of UMIST type(with axially grounded shield electrode)and METC type(with axially driven shield electrode)are established.Based on the three-dimensional physical model,the mathematical expressions of measure capacitance value and sensitivity are derived.The capacitance influence rate and sensitivity influence coefficient are defined,and the influence of the axial shield electrode is analyzed on the capacitance value and sensitivity for an oil-air lubrication system.On this basis,the relative error of image(IME)and the image correlation coefficient(CORR)are used as evaluation criteria for image reconstruction.The results show that the capacitance influence rate characterizes the sensitivity of the sensor,both axial shield electrodes can eliminate fringing capacitance and improve the sensitivity of the sensor.Sensitivity influence coefficient characterizes the uniformity of sensor sensitivity.The Oil-air lubricated ECT sensors with axially grounded shield electrode makes the sensitivity more uniform,while it with axially driven shield electrode has the opposite effect.METC type of ECT sensor is more suitable for the recognition of annular flow in oil-air lubrication,and the quality of the reconstructed image is the highest.(3)The three-dimensional physical model of the oil-air lubricated annular flow pipeline and its ECT sensors of UMIST type is established;The influences of four characteristic parameters(the thickness of the pipeline,the length of the capacitive electrode,the length of the axial shielded electrode and the depth of the radial shielded electrode)on the performance of the sensor are analyzed and their optimization ranges are determined.The sensor performance optimization function is constructed through sensitivity influence coefficient and capacitance response ratio.The optimal values of the above four parameters are determined by the response surface methodology.On this basis,through the relative error of image and the image correlation coefficient,the quality of the reconstructed image is evaluated to verify the reliability of the optimized sensor.The research results show that the image error obtained by the optimized sensor is significantly reduced.