Study On Flow Law And Clustering Characteristics Of B Particles In The Spout-Fluid Bed

Spout-fluid bed（SFB）is a typical gas-solid contact equipment,which has shown great application prospects in chemical industry,energy,materials,food and other fields.The research on the macro flow law and Mesoscale Characteristics in the bed is of great significance for optimizing the existing process operation and expanding new application scenarios.Most of the existing researches focus on the macro flow law and characteristic parameters,and the material types are limited to Geldart D and other specific scenarios.Therefore,based on the visualized rectangular spout-fluid bed test platform,this paper carried out the experimental research on B particles from three aspects:the transformation law and characteristics of gas-solid flow structure,the multi factor influence mechanism of transformation speed,the clustering law and characteristics of particles,and the study of spout-fluid bed is introduced into mesoscale range by means of image method.The main conclusions are as follows:（1）In the spout-fluid bed,eight typical gas-solid flow structures outside the fixed bed were clearly distinguished and defined by pressure fluctuation signal analysis and visualization unit image processing:Internal jet,bubbling fluidization,slugging fluidization,spouting,spouting with aeration,spout-fluidizationt,turbulent fluidization,unstable structure（unstable spouting and unstable slugging）.Three typical gas-solid flow structures,including bubbling fluidization,slugging fluidization and turbulent fluidization,are analyzed in detail in time domain and frequency domain,including the difference between spouting region and annular region,and the influence of increasing fluidization gas on gas-solid flow characteristics.（2）The phase diagrams of four particle size particle flow structure are established.It is found that the flow law of B particles is common in general.With the increase of d_p,the range of internal jet,spouting and spout-fluidizationt increases,and the range of turbulent fluidization decreases.Compared with the D particles,the gas-solid flow structure of turbulent fluidization can be obtained by keeping the appropriate spouting velocity（usually less than the minimum spouting velocity）and increasing the U_f uniformly.There are two different paths to the transition of turbulent fluidization.At low spouting gas velocity,the gas-solid flow structure with uniform increase of U_f is the same as that in the front section of D particles,while at high spouting gas velocity,the gas-solid flow structure with uniform increase of U_f is the same as that in the back section of D particles.（3）U_c is determined by the standard deviation of pressure gradient,it is found that the increase of H₀,the increase of d_por the decrease of H will lead to the increase of U_c in varying degrees;The variation of U_c with U_s or D_i shows an"S"type trend.Based on the existing research,two new dimensionless correlations of U_c prediction are established by introducing D_i and U_s.（4）Five typical particle clusters appearing under turbulent fluidization conditions in the spout-fluid bed are defined by image method with shape and structure recognition:Inverted U-shape,U-shape,core-annulus structure,banding-shape,nets-shape,and analyze the causes of its formation and reveal the law of its development and evolution respectively.The particle cluster fraction（F_c）is proposed and defined to quantify the degree of cluster in the bed,it is found that F_c increases with the increase of H₀ and d_p,presents an"S"type change trend with the increase of D_i,and decreases first and then increases with the increase of H;The effect of U_s and U_f is characterized by gas velocity ratio.For a fixed total superfical gas velocity,with the increase of U_s ratio,F_c went down firstly and then up with a minimum value.