Study Of Particle Flow Paramaters Measuremnt With Laster Backscattering

Gas-solid flow widely exists in many fields such as power,chemical,pharmaceutical and metallurgy industries.The accurate online measurement of the flow parameters(velocity and concentration)is of great significance for the safety,economy and efficiency of these industrial processes.Present particle flow measurement techniques have their own advantages and disadvantages,and few of them can meet the requirements of online particle flow measurement under harsh industrial conditions.In this work,an on-line particle flow parameter measurement system is studied and developed based on laser backscattering principle in combination with optical fiber probe.Laboratory calibration and experiments on a turbulent fluidized bed are carried out to evaluate the developed measurement system.Firstly,the light scattering theory is introduced in detail,especially the Mie scattering and Rayleigh scattering theories.Based on Mie scattering theory,the intensity distribution of the scattered light is deduced.The characteristics of the particle backscattering are explained,as well as its applicable conditions.According to the concentration measurement and data sampling principles,the discrete formulas of particle concentration and velocity are further derived.Secondly,an online measurement system based on the optical fiber probe is designed and developed,consisting of power supply system,optical system,photoelectric conversion and signal modulation system,data acquisition and software program for data processing.Optical system,comprised of laser,optical fiber connector,optical fiber beam and photoelectric coupling components,realize the coupling and transmission of laser light and the collection of the scattering light.The photoelectric conversion and signal modulation system is used to convert the scattered light signal into a voltage signal.The software program,based on NI data acquisition card(NI-6353)and LabVIEW development environment,can sample and process the voltage signals,and further display real-time measurement data of particle concentration and velocity.Finally,the experiments are carried out to evaluate the performance of the developed system on a gravity conveyor and a turbulent fluidized bed.By calibrations on the gravity conveyor,the relationship between particle concentration and the output voltage of the measurement system are determined,as well as the measurement error of particle velocity.With the calibrated results,the spatial distribution of particle concentration and velocity within the turbulent fluidized bed are measured at different flowrates of fluidization air.Experimental results show that the developed system is capable of measuring the particle concentration and velocity with high stability and reliability.Furthermore,the measurement system can monitor and characterize the flow phenomenon such as ring core flow and particle backmixing within the turbulent fluidized bed.