Gas-Solid Two Phases Flows Parameters And Particle Electrostatic Measurement

The on-line measurement of gas-solid flows parameters is of great importance for understanding the nature of two-phase flows and the safety, economic operation of industrial process. But it has great difficulty in measuring the flow parameters due to the complicated and random nature of gas-solid two phases flows process. At present, the measurement techniques for gas-solid two phases flow have become a desiderative problem to be solved in multi-phase field. Electrostatic sensing technique for particle velocity, concentration and flow rate, which is based on particle electrification of gas-solid two phases flow, was put forward abroad in 1960's. Though the electrostatic method has been applied in the measurement of gas-solid flows parameters, there are still some problems to be examined in both theoretical and experimental respects. The present contribution mainly centers on the finite element simulation investigation on the electrodynamic sensor, the detection of weak electrostatic signal, the design of measurement and test system and its application in gas-solid flow parameters and particle electrostatic measurement.Firstly, on the basis of the existing fundamental measurement models of electrodynamic sensor, an improved mathematical model based on point charge concept was proposed, in which the physical geometry of the electrode, the material property of insulation pipe and the geometry size of electromagnetic screening are included. The model describes the sensing mechniasm of the sensor more accurately, which provides the theoretical basis for the performance analysis and optimum design of electrodynamic sensor.Secondly, as for the complication of mathematical model of the sensor, the effects of physical geometry of the electrode, material property of insulation pipe, the geometry size of electromagnetic screening and the distribution of the transported medium in the pipeline on the sensing characteristics were discussed in detail using the finite analysis software ANSYS. Furthermore, the spatial filtering effect of electrodynamic sensor was analyzed quantitatively and the effect of insulation pipe charging on the sensing electrode was also discussed theoretically.Thirdly, a sensing circuit of electrodynamic sensor was designed based on weak signal detection theory, and the frequency response characteristics of measureent system were also investigated. Experimental results show the interface circuit can realize the real time measurement of electrostatic weak signal and the measurement system acts as a band pass filter.Finally, the electrostatic sensing technique was applied in the measurement of particle electrification, particle velocity and mass flow rate. The charging process of pneumatically transported particles is very complicated. It is of utmost value for insuring the safety operation of industrial equipment to study particle electrification phenomena. The measurement system was used to detect the electrostatic characteristics of coal particle in dense phase pneumatic transport system under high-pressure. A measurement method for solid particles mean velocity based on the filering effect of electrodynamic sensor is introduced. And the effects of geometry parameters of sensor, particle velocity distribution, particle concentration distribution on the cross section of pipe, particle size, particle material type and frequency resolution on the mean velocity measurement of particles were also investigated theoretically. The fundamental theory and experimental results on a gravity-fed particles flow and the...