Measurement Of Bubble And Droplet Size Distribution In Gas-Liquid Two-phase Flow By Digital Imaging Technique

Gas-liquid two-phase flow is widely used in many fields such as energy,chemical,petroleum,refrigeration,aerospace,environmental protection,and life sciences.Bubbles and droplets in gas-liquid twophase flow determine the gas-liquid phase contact area and phase-to-phase mass transfer and heat transfer,which directly affect the reaction rate of industrial reactor.Therefore,the measurement of the bubble and droplet parameter is of great significance for process control and gas-liquid two-phase flow system optimization.In this paper,a measurement technique for bubble and droplet size distribution based on digital image processing is proposed and applied to study bubble characteristics in bubbling column and spraying droplet distribution characteristics.Experiments are carried out to evaluate the measurement technique.Firstly,the image preprocessing methods such as image filtering,image enhancement,binarization and digital morphology of sparse bubbles are introduced.The effects of different image filtering,enhancement and binarization techniques are compared.The median value,filtering,image linear transformation enhancement,Dajin method binarization and Canny algorithm edge extraction technology route are combined to extract the bubble characteristic parameters.To solve the overlapping problem of dense bubbles,a bubble segmentation and contour reconstruction algorithm based on curvature calculation for pit matching and circle fitting is proposed.The image after bubble segmentation is reconstructed,which decreases the measurement error of the overlapping bubbles.Secondly,a bubble column is built,and the bubble size distribution of the bubbling bed is experimentally studied.The bubble distribution and contour reconstruction algorithm based on the concave matching and the circumferential fitting are used to analyze the bubble size distribution.The results show that the algorithm can not only extract the bubbles with clear and complete particle contours from the image,but also accurately segment the overlapping bubbles.The bubble size distribution can further be calculated.As the gas flow rate increases,the number of small bubbles increases sharply while larger bubbles are produced.The maximum and Sauter diameter of the bubble increase with increasing gas flow.Then,a rotor type burner is built and the spraying droplet size distributions based on digital imaging are measured.The experiments are carried out to study the spraying characteristics of the rotor type burner.The influence of parameters such as rotor cup speed and fuel quantity on the spraying droplet size.Results show that in the spraying field,the size of the fuel droplets decreases firstly and then increases with the distance from the nozzle.The spraying oil droplets are uniformly distributed in a small size range.The size of the droplets decreases with the increase of the rotor speed and the primary air flowrate.Finally,the software of particle size distribution(bubble and droplet)is designed and developed on the platform of MATLAB/GUI.The software has the following functions: firstly,the image preprocessing function can achieve the enhancement of the particle image.Secondly,the imaging algorithm for particle size distribution is integrated in software to achieve statistical measurement of particle size distribution;Thirdly the software has the image batch processing function,which can analyze particle size distribution in different scales.