Determination Of Spatial Sensitivity Of Electrostatic Sensors Based On COMSOL Simulation And Their Optimal Design

Gas-solids two-phase flow plays an important role in the natural and industrial processes.Because of the complexity and randomness of the gas-solids flow,it is difficult to measure the flow parameters of the fluid.As a new detection method,the electrostatic method has the advantages of the low cost,easy maintenance and high sensitivity in measuring of gas-solids flow.It is very important for electrostatic sensors to have homogeneous spatial sensitivity.However,most of them do not have such intrinsic properties.The ring-shaped electrostatic sensor is a non-invasive sensor which does not obstruct the flow of the fluid and avoid electrode wear.However,it has the disadvantage of inhomogeneous spatial sensitivity.In this paper,a method for the spatial sensitivity homogenization of electrostatic sensors based on frequency characteristics of electrostatic signals was put forward.A simulation model of a ring-shaped electrostatic sensor was built by COMSOL software,the electrostatic field and the spatial sensitivity distribution of the sensor were obtained.Further experiments were conducted on the belt-type electrostatic induction test rig and the particle drop test rig.The primary contributions are as followed:1.In this paper,based on the difference of frequency characteristics of the electrostatic signals between different radial positions,a method of harmonic wavelet transform was proposed.The experiments were conducted on a belt-type electrostatic induction test rig.The relationships between the bandwidth of the electrostatic signal and the velocity and the position of the belt were analyzed.Based on the difference of the frequency characteristics between different positions,the harmonic wavelet decomposition was applied to the electrostatic signals from the corresponding upstream arnd downstream electrodes and the signals after the decomposition are cross-correlated to determine the belt velocity at different positions.Therefore,the feasibility of the method was verified by comparing with the actual belt velocity.2.In order to study the spatial sensitivity distribution of electrostatic sensors,three dimensional simulation models of the electrostatic sensors were built.According to the different simulation parameters,the effects of the single particle and multiple particles' motions on the spatial sensitivity distributions at different radial positions were analyzed.Based on the difference in the frequency characteristics of single particle,the mixed electrostatic signals were decomposed by harmonic wavelet transform.In order to improve the homogeneity of spatial sensitivity,the components of electrostatic signals from different radial positions were compensated and reconstructed based on the spatial sensitivity of the electrostatic sensors.3.In this paper,the experiments were conducted on a free-fall particle flow test rig to verify the homogenization of the spatial sensitivity of electrostatic sensors.The electrostatic signals of single particle and the roping flow of were collected by ring-shaped electrodes.The relations between the widths of the electrode and the bandwidth of the electrostatic signals and the RMS values were analyzed.Based on the difference in the frequency characteristics,the mixed electrostatic signals were decomposed by harmonic wavelet transform.The RMS values of the electrostatic signal before or after compensation and reconstruction were compared.Thus,the homogenization of the spatial sensitivity of electrostatic sensors based on harmonic transform was evaluated.