Optimization Of Capacitance Sensor Based On Numerical Simulation And Design Of Experiment

The pneumatic conveying solid particles is a typical gas-solid two-phase flow.Phase concentration is an important parameter to reflect the flow state of gas-solid two-phase flow.The online detection of phase concentration is of great significance to the production measurement and process control in the process of dense phase pneumatic conveying.Due to the complex flow process,the interaction between flow field and electric field,the existence of edge effect and standing capacitance,it is difficult to measure the solid phase concentration accurately.In order to improve the precision of concentration measurement,it is necessary to optimize the design of structure for capacitance sensor.This thesis was set in the condition of multi-physical field coupling,taking the multiphysical field software COMSOL as the research platform The capacitive phase concentration sensor was used as the research object.The thesis made a deep discussion on the sensor optimization based on the edge effect and standing capacitance,which made use of the simulation and experiment validation.The main work of this thesis is showed as follow:(1)Based on the advantages and disadvantages of several phase concentration sensors,the parallel surface capacitance sensor was taken as the research object.In view of the edge effect and standing capacitance,the sensor with axial and radial guard plate was proposed to improve the measurement precision of the phase concentration sensor.(2)Based on the multi-physical fields coupling method,the coupling effect of flow fieldelectrostatic field was analyzed and studied.The rapid modeling of the capacitive sensor was realized based on MATLAB script with multi-physical field software COMSOL,which was taken as simulation platform.(3)Based on the numerical simulation and experimental design method,the capacitance sensor with radial and axial guard was built with a three-dimensional finite element model in COMSOL.The influence of structure parameter of sensor on the sensitivity field of sensor was analyzed in detail.The critical parameters were selected by factorial design.The multi-obj ective optimization of the capacitance sensor structure was realized based on the response surface method with the radial uniformity error and axial uniformity error as the optimization objective,which reduced the influence of flow pattern on the measurement.(5)In the condition of multi-physical fields(flow field-electrostatic field coupling),the typical flow pattern in the dense phase pneumatic conveying of horizontal pipeline is simulated and the output characteristics of the capacitance sensor were studied with the flow pattern,which laid a foundation for sensor measurement with flow pattern.(6)The optimized sensor structure was verified by simulation using the test bar with different radius which represents different volume concentration in COMSOL.In the lab condition,sensors and the test bars with different radius were made.The experiment results were proved that the static test results are inconsistent with theoretical results.The edge effect and standing capacitance were greatly reduced,and the measurement error is within 10%,which met the need of phase concentration measurement.