Coating Mechanism Of Hot Melt Fluidized Bed Based On Population Balance Model

Hot melt fluidized bed coating is an advanced technology for preparation of microencapsulation.However,the process of particle coating is still an experiential unit operation,and the research on the mechanism of coating is not yet clear.The most important thing is lack of safe and reliable theoretical guidance for industrial operation.In this study,Computational Fluidized Dynamic coupled with population balance model coupling method was used to simulate the binding mechanism of molten droplet and fluidized solid particles during the process of hot melt fluidized bed coating.And the preparation of lipophilic microcapsules was taken as the research object in this study.The factors affecting the coating effect of the hot melt fluidized bed are the atomization degree of the droplets in the fluidized bed,the fluidization degree of the coated particles and the motion state of the droplets when they contact with the particles.In order to study the factors that influence the coating effect of hot melt fluidized bed.So as to further optimize the hot melt fluidized bed coating process.The geometric model used in this study is conical fluidized bed.Numerical simulation that was carried out by coupling computational fluid dynamics with population balance model was used to investigate the atomization process of droplet.In order to further study the influence factors of droplet contact with particle.And computational fluid dynamics and discrete element method were coupled to simulate the contact process between droplets and particles at four fluidization velocities(umf,1.5umf,2.5umf,3.5mf).Two dimensional numerical simulation of droplet atomization in fluidized bed was carried out through population balance model.Compared with the calculation results of discrete phase model,the same velocity field distribution can be obtained by population balance model and discrete phase model.Therefore,population balance model can be used as an alternative model of discrete phase model,and further study the coalescence and breakage behavior of droplets.Moreover,a more detailed particle size distribution can be obtained by population balance model.The temperature in the fluidized bed is low in the middle and high in both sides.The temperature near the wall is very low,and the droplet generates reflux.The droplet is easy to agglomerate in this area.However,in the central area,the droplet velocity is larger,and the temperature will not drop abruptly.The breakage behavior is more obvious.The research in this paper provides a good theoretical basis and research basis for the coating process of particles.Under the assumption that droplets are particles,the process of fluidized bed coating can be basically realized through coupling of discrete element method and computational fluid dynamics.and this process can be used to study parameter changes in fluidized bed coating process.Through the simulation of droplet atomization process by population balance model,we know that droplet will also coalesce and break during the atomization process.When droplets are contacted with particles,the velocity of particles will be combined with the velocity of droplets,which will continue to coalescence and breakage.Therefore,we can get more contact times between droplets and particles than top spray,and 1.5umf is the ideal condition,that is,the top spray condition is superior to the middle spray condition.