Analytical Study On The Turbulent Agglomeration Prcess Of Non-spherical Ultrafine Particles

Non-spherical fine particles belong to Geldart C-type particles.Although their fluidization is difficult,the fluidization technology of non-spherical fine particles is increasingly important due to the huge development prospects.In order to obtain the macroscopic change of fine particle flow and the microscopic change of agglomeration,this paper considers coupling the gas-solid two-phase flow model and the group balance model to solve.In order to overcome the non-spherical characteristics of agglomerates,this paper uses different fractal dimensions to represent the non-spherical characteristics of agglomerates.In order to make the simulation results closer to the real situation,in this paper,the collision efficiency,the root mean square coupling method and other factors are considered to improve the traditional agglomeration core.In this paper,two typical gas-solid fluidized reactors:turbulent coalescer and gas-solid fluidized bed were numerically simulated.Aiming at the phenomenon of particle agglomeration fluidization,macroscopic fluidization and agglomerate size distribution were studied and analyzed respectively,and the ideal agglomeration core and the improved agglomeration core were analyzed and discussed through numerical calculation.In the process of agglomeration of fine particles caused by physical action,there are different agglomeration mechanisms.According to the scope of action of the agglomeration mechanism,combined with the fractal theory,collision efficiency and root mean square coupling,this paper first determined the improved agglomeration kernel function,and then based on MATLAB software to study the fractal dimension,temperature and root mean square coupling The effect of the method on the improved agglomeration kernel function,and the effect of Stokes number and particle size on the collision efficiency.The results show that the consideration of fractal dimension can effectively reduce the effects of overestimation of turbulent cluster nuclei and underestimation of Brown cluster nuclei.The fractal dimension of the turbulent agglomerate core has a greater impact on large particles,and the fractal dimension of the Brown agglomerate core has a greater impact on small particles;Brownian motion has a huge effect on particles with a particle size of less than 2 μm.The Brownian motion cannot be ignored during the fluidization of the turbulent coalescer.As the temperature rises,the Brown agglomeration is strengthened to some extent,but the increase decreases with the increase of the particle size;as the St number increases,the collision efficiency will increase.As the particle size increases,the collision efficiency will decrease;the root mean square method is more reasonable than the linear addition method.After determining the improved agglomeration core model,this paper customizes the improved agglomeration core function based on the UDF function of Fluent software,and uses the Euler two-fluid model coupled with the group balance model method for the turbulent coalescer and gas-solid fluidized bed.The agglomeration fluidization process is numerically simulated,and a grouping algorithm is used to solve the group balance equation.The results show that the dissipation rate in the vortex region of the turbulent coalescer is significantly increased,and the particle motion becomes multi-fluidized,which enhances the agglomeration effect;a new cluster established by introducing collision efficiency and fractal dimension Df The cluster model is more in line with the actual situation;the simulation results of the improved cluster model are closer to the experimental results.