Design Of Gas-Solid Two-Phase Flow Velocity Measurement System Based On Array Electrostatic Sensor

Gas-solid two-phase flow is widely used in industrial processes,such as power plant pulverized coal transportation,steel mill blast furnace dusting system and grain conveying,which the powder velocity is an important parameter to describe these processes.However,the temporal and spatial variations of gas-solid two-phase flow velocity are unevenly distributed,which make the velocity measurement unable to reflect the true velocity of particles in the pipeline.Therefore,the realization of gas-solid two-phase flow velocity measurement,especially the velocity distribution measurement is a difficult issue.Electrostatic sensors have the advantages of simple structure and low price,which have broad application prospects in the measurement of gas-solid two-phase flow parameters.Based on the principle of electrostatic induction,the thesis designs two kinds of array electrostatic sensors,and sets up the signal detection circuit and data processing platform,which finally completes the real-time measurement of the local average velocity of solid particles.The main work is as follows:(1)The mechanism of electrostatic generation is deeply studied,and the principle of electrostatic sensor speed measurement is deduced theoretically.The time-frequency relationship of nonlinear and unstable electrostatic wave signals is analyzed by power spectrum and amplitude phase spectrum.Two kinds of array electrostatic sensors are designed based on cross-correlation algorithm and spatial filtering algorithm.The number,shape,axial width,upstream and downstream distance and coverage angle of the section electrodes are determined by experiments.(2)A combined interpolation algorithm using Hilbert transform and FFT interpolation is adopted to improve the time resolution of cross-correlation curve,which is verified by experiments.The spatial filtering effect of the electrostatic sensor is deduced in theory,and the extraction of the center frequency of the electrostatic signal is realized by using FFT transform and combining with the experiment.(3)According to the characteristics of low frequency and weak amplitude of electrostatic signal,a signal detection circuit is designed.mainly include:preamplifier circuit,high pass,notch and low-pass filter circuit,summing circuit and limiter circuit;Multisim 14.0 is used to simulate the various parts to determine the multiplier K preamplifier circuit,the notch filter feedback factor F and the low pass filter circuit quality factor Q.(4)The design completes the STM32 ARM with Cortex-M3 as kernel,and realizes AD conversion,data cache,and RS-485 serial communication function.In the LabVIEW environment,the PC software platform is built to realize VISA serial communication,FIR digital filter,combined interpolation cross-correlation algorithm,spatial filtering algorithm,and human-machine interface function.(5)The experiment platform is set up,and determines the sampling frequency and the number of sampling points through the experiment.According to the cross correlation algorithm,the experiment of the correlation of different position plates is completed under the gravity measurement system,and the velocity distribution is measured by the same side plate.According to the spatial filtering algorithm,the velocity distribution measurement experiment of 4 electrode array is completed under the gravity measurement system.The velocity of the two algorithms is calibrated by using a belt experimental platform,the results shows that the relative errors of the velocities measured by the two algorithms are respectively within 5%and 10%.