Research On Structure Design And Multi-objective Optimization Of Capacitance Sensor

The concentration is an important parameter which reflects the flow information of gas-solid two-phase flow.By means of detecting the solid phase concentration in the pipeline online,it can help to achieve production metering or process controlling.Since detection of capacitance sensor is dependent on the flow pattern,which is changeable in the complex process of two-phase flow,it is difficult to measure the solid phase concentration accurately.In order to improve the precision of concentration measurement,optimization design of structure and installation position is necessary.This thesis was set in the dense phase pneumatic conveying process,taking the finite element software ANSYS and fluid analysis software FLUENT as the research platform.The research object was capacitive phase concentration sensor.The thesis made use of the research method on the simulation and experimental validation and made a deep discussion on the sensor optimization based on relation sensibility and homogeneity error.The installation position of the sensor in the pipeline is optimized by combining the output characteristics of the capacitance sensor with different flow patterns.The main works as follow:(1)Based on the advantages and disadvantages of several phase concentration sensors whose were applied universally,a new type capacitance sensor with eight plates was put forward,which based on the same section formed field rotation and has the low uniformly error and the small size.(2)The capacitance sensor was built with a three-dimensional finite element model in ANSYS.The influence of sensor plate number,excitation mode and shielding method to sensitivity field of sensor was analyzed in detail.The structure parameters of the sensor were optimized by the orthogonal test.(3)Based on the above research results of finite element simulation,a multi-objective optimization method of capacitance sensor was studied,by which the optimal design of the capacitance sensor structure.The method made the relation sensibility,the radial and axial homogeneity error as optimization objective,and made the output capacitance dynamic range,the ratio of the maximum and minimum output capacitance as the constraint condition.(4)The typical flow pattern of dense phase pneumatic conveying was simulated in FLUENT.Capacitance sensors' output signals of different flow patterns were analyzed,which laid the foundation for optimization the installation position.(5)In multi physical fields conditions(flow field coupling with electric field),mathematical model of gas-solid two-phase flow in horizontal-to-vertical upward pipe was established.The influence of the physical parameters of particle phase and operating conditions were got by simulations.The installation position of the sensor in the pipeline was optimized.(6)The optimized sensor structure was verified by simulation using the flow pattern of central flow with different volume concentration in ANSYS.In the lab condition,sensors were made according to simulation results;Several central flow models with different concentrations were made.The experiment results were proved that the static test results are consistent with theoretical results.The sensor had good uniformity which can satisfy the need of dense-phase pneumatic conveying.