Research On The Measurement Method Of Velocity And Concentration For Gas-solid Two Phase Flow Based On Ring-type Capacitance Sensor

Gas-solid two phase flow in pneumatic transmission is widely used in the field of metallurgy,electric power and chemical industry.The measurement and control for the flow parameters of gas-solid two phase flow has important significance on the quality of products,the stability of production process and energy conservation.Velocity measurement methods of gas-solid two phase flow mainly include cross-correlation,spatial filtering,Doppler method and so on.Because of the simple measurement installation and convenient data processing,spatial filtering method has been widely studied.In comparison with other principles,the capacitive sensing approach is widely used for its advantageous behavior in terms of noninvasive sensing,costs and harsh environment capabilities.So in this dissertation,a ring type capacitive sensor has been presented to measure concentration and especially for velocity of gas-solid two phase flow based on spatial filtering method.The main works are as follow:(1)The calculation model of the spatial sensitivity function for capacitive sensor based on spatial filtering method has been established by numerical simulation and regression analysis method.The spatial filtering characteristics of capacitance sensor has been analyzed based on the calculation model.To optimize the sensitivity and the spatial filtering characteristics of capacitance sensor,the sensor structure parameters such as the number of electrode,electrode width,the distance between adjacent electrodes,the radius of screening can are also deeply studied based on the FEM software.(2)A differential combination velocity measurement method has been proposed according to theoretical analysis and mathematical deduction.The new method was beneficial to improve the sensitivity and the signal to noise ratio of the system,in the meantime to remove the pedestal component which affects the accuracy of velocity measurement by deviating the central frequency.(3)The signal detecting circuit has been designed based on AC excitation principle.Each part of the circuit has been confirmed according to the specific way of measurement.Software program based on Lab VIEW and virtual instrument technology is written to accomplish signal acquisition,signal processing,waveform display and waveform replay.(4)Flow parameters measurement system for gas-solid two phase flow has been established.Under the laboratory environment,the experiments of relevant measurement methods were done to verify the theoretical analysis.The experiments' results indicate that the system has the feasibility of velocity and concentration measurement.