Study On Measurement For Velocity Vector Field And Granularity Distribution Of Multi-phase Flow Based On Single-frame And Single-exposure Imaging

Many problems of measurement for velocity and granularity of multi-phase floware increasingly prominent in the modern industry such as dust monitoring, granularitymeasurement for powder, flux control for conveying. Existing measurement techniqueshave not met the requirement of on-line or field measurement or cost control.Therefore, it is significant for the development of multi-phase flow measurementtechniques to study a method measuring velocity vector field and granularitydistribution of multi-phase flow with simple system, low price and visualization.Particle imaging velocimetry (PIV) has been the main measurement approach inthe fluid and heat transfer experimental research with expensive device andcomplicated system. In order to get the clear particle movement image, PIV makes theexposure time very short. In fact, the particle movement blurred image with relativelylong exposure time also contains the information of velocity and granularity. The fuzzylength of movement image is regarded as the moving distance of particle with theexposure time and the direction of trajectory as the velocity direction. The width oftrajectory is related to the particle size. So the flow field results can be obtained fromthe single-frame and single-exposure image using the imaging measurement systemwith low cost and simple equipments and controlling exposure time.The multi-phase flow measurement technique based on single-frame andsingle-exposure imaging has got the advantages of PIV and high speed photography.This method appeared in the eighties of last century, which only can do qualitativeanalysis limited to the software and hardware level. With the swift development oflaser, semiconductor light-emitting and image sensor technology, the imagingmeasurement technique has much more application in the field of multi-phasemeasurement. With the development of digital image transmission and computertechnology, clearer images and faster-processing results can be got. This paper studiesthe algorithm of single-frame and single-exposure imaging technique and introducesthe system design and parameter selection and do experimental analysis of theinfluence on velocity and granularity between laser sheet light and LED backlight.This paper summarizes the former research on measurement techniques forvelocity vector field and granularity of multi-phase flow. The model of two-phase flowmovement based on single-frame and single-exposure blurred image is established.The discipline for grey value distribution of moving particle image is studied. The principle and image processing algorithm of measurement for velocity and granularityof particles are presented. Two-dimensional imaging for multi-phase flowmeasurement system is set up and the calibration of imaging measurement devices isdone. The paper presents two experiments including the particle sedimentation in theair and liquid-solid two-phase flow past the cylinder and measures the velocity vectorfield and granularity distribution of disperse-phase in the gas-solid and liquid-solidtwo-phase flow using this method. The experimental results are in agreement with thetheoretical results, which illustrates this method can be used to measure the velocityvector field and granularity distribution of multi-phase flow and has high reliabilityand accuracy.