Research On Bubble Evolution Behavior And Optimal Control Of Flow Structure In Gas-soild Fluidized Bed

According to the characteristics and current research methods of particle fluidization process in gas-solid fluidized bed,the behavior of particles and bubbles in fluidized bed is studied in this paper.Because the gas-solid fluidized bed has excellent performance of mass and heat transfer,it has attracted extensive attention of scholars.The rise of bubbles in gas-solid fluidized bed is periodic,and the movement of bubbles is always irregular,which leads to different effects of bubbles at different positions on particles.Due to the different behavior of bubbles,the effect of particles on bubbles is different,and the particle size distribution will also affect the volume of bubbles.Therefore,in-depth study of the relationship between particle motion and bubble behavior is of great significance to the development of gas-solid fluidized bed in practical industry.The experimental part builds a visual experimental platform based on the PIV test system,which includes five parts:a fluidized bed made of acrylic,a fan,a rotameter,an image capture system and a particle image velocimetry（PIV）.In this paper,based on the CFD-DEM method,the fluidized bed is calculated under the Euler-Lagrangian framework.The main research contents of this paper are as follows:（1）The two-phase motion in gas-solid fluidized bed is unsteady,so the summary of the motion law of bubbles and particles is still not perfect.In this study,according to the cfd-dem method,which can capture the movement characteristics of a single particle,and combined with the advantages of PIV in capturing particle flow,the characteristics of bubble behavior in fluidized bed are analyzed from the perspective of micro particles.It is found that the particle flow caused by bubble breaking and particle reflux will lead to small gas resistance and affect the gas flow.Changing the speed of intake air,there is a transition speed between single bubble and multiple bubbles between 3 U_mfand 2.5 U_mf.Under the condition of 2.5 U_mf,the bubble area decreases with time,and when the bubble area decreases to about 47%of the maximum bubble area,the bubble area will increase again.（2）The interaction between particles in the fluidized bed will have a very important impact on the behavior of bubbles,and the role between particles with different particle sizes is not clear.Therefore,the control groups with particle size mass ratio of 9:1,1:1 and 1:9 are set in this study to study the influence of particle size on the fluidization structure by the combination of cfd-dem simulation and PIV experiment.It is found that the existence of large particles will stabilize the fluidization process,and there is a fluctuating trend in the change of bubble shape.The increase of the proportion of large particles makes the overall particle velocity smaller and smaller,which weakens the force between particles,but makes the particles easier to flow.Finally,the third kind of small particles was added to the 1:1 control group.It was found that small particles weakened the phenomenon of difficult mixing between particles.In this study,the behavior of particles and bubbles is studied through the fluidization process of particles in gas-solid fluidized bed.It is found that the movement of bubbles in the fluidized bed will interact with the accumulation of particles,and the existence of small particles will promote the mixing between particles and gas.This has an important guiding role for the study of the behavior of particles and bubbles in gas-solid fluidized bed,and provides a certain reference for the study of particles in industrial gas-solid fluidized bed.