Research On Gas-solid Two-phase Flow Characteristics And Nonlinear Characteristics Analysis Of A Riser

In recent years,with the development of science and technology,as one of the most important forms of multiphase flow,gas-solid two-phase flow has been widely used in many fields,such as electric,power,coal,chemical industry,pharmacy,food and so on.However,due to the complexity and variability of the phase interface of gas-solid two-phase flow system,as well as the interface velocity and other effects,it has been usually characterized by strong nonlinearity and instability.This has hindered the further understanding of gas-solid two-phase flow characteristics and coupling mechanism,which has restricted the optimization of industrial equipment and the improvement of production efficiency and made the engineering need lagged behind the basic theory research.Therefore,it is necessary to use advanced parameter detection technology and modern analysis method to proceed from the gas-solid two-phase flow process.Then flow characteristics and nonlinear characteristics of the system will be understood deeply.It is of great significance to supplement the basic theory of multiphase flow and to guide the optimization and amplification of industrial reactor structure.The pressure signals and flow pattern images were collected on the experimental platform of circulating fluidized bed riser,then the differential pressure method,digital image processing technology,multi-source information fusion theory,fractal theory,chaos theory and recursive analysis method were used to analyzed the flow characteristics of the system.For example,axial pressure gradient and particle concentration distribution in the riser was researched.The flow behaviors,distribution structures and concentration of the particles in the local region were measured.The fractal characteristics of multi-source information were analyzed and contacted.Besides,influence of different agglomerates on chaotic characteristics of the two-phase flow system was discussed.Firstly,the differential pressure signal between different positions of the riser was detected.The axial pressure gradient and the particle concentration distribution in the riser were researched.It is found that the pressure gradient and particle concentration decrease gradually with the increase of axial height.The trend of inhomogeneous distribution of pressure gradient and particle concentration is weaken with the increase of the operating gas velocity.Besides,total pressure drop is also decreased.Secondly,the images of gas-solid two-phase flow at the bottom of riser were recorded by high speed camera.The digital image processing of the image samples were carried out,then the movement behavior and distribution of the particles in different fluidization conditions were analyzed,the effect of the air supply mode on the particle motion was found.In the state of slugging and turbulent bed,the particles respective show a plunger flow structure and a clockwise internal circulation structure.Otherwise,based on the high-speed photography and digital image processing technology,the detection of local particle concentration in dilute phase conveying process was realized.Thirdly,two parts of information including differential pressure signals and image were integrated.Based on the fractal theory of nonlinear analysis,the physical meaning of each scale signal was discussed from the view of multi-scale analysis,and the fractal characteristics of the two kinds of information were contacted.Finally,the agglomeration phenomenon was produced by injecting the solution of sugar water into quartz sand particles.The structure of the generated agglomerates was identified.The mechanism of the system's chaotic characteristics affected by the kinds of agglomerates and the circulation flow of particles in slugging bed stage and turbulent bed stage was researched by means of recursive analysis method.The result shows that trend along the diagonal line is significant in the slugging bed,the system has strong periodicity and can hardly be affected by the kind of the agglomeration.Moreover,in turbulent bed,as the increase of particle circulation flow,for original quartz sand and micro agglomerates,the trend along the diagonal line is enhanced in the recurrence plot,while the determinacy is improved and the bifurcation is reduced,which reflects the system chaotic characteristic is weaken.For nucleation agglomerates,the structure and parameters of recurrence plots are hardly changed,which shows the chaotic characteristics of the system is hardly affected by particle circulation flow and agglomeration kinds.For cementation agglomerates and paste agglomerates,the isolated points in the recurrence plot are increased,the determinacy is decreased and the bifurcation is enhanced,which reflects that chaotic characteristic of the system becomes stronger.