Simulation And Test Of The Flow Flied During Particle Coated Process By Supercritical Impact Flow

During particle coated process, the functional layer can be formed on the surface of the host particle. So the surface characteristics can be modified so as to achieve slow releasing, good weather resistance and monodispersion with the host particle keeping its completeness. It has profound influence to the medical, engineering materials, and other relative areas. The traditional coated process will cause agglomeration of the fine particles. In addition, the liquid used in the coating process is hard to be wiped out, which will lower the quality of the products. Using rapid expansion of supercritical solution combined with impact flow techno-logy is a new method for coating particles. This method can reduce the agglomeration of the particles and get products with high purty. This paper studies the fluid flow characteristics and influencing factors to coated effect during the particle coated process by supercritical impact flow. The specific contents list as follows.CFD software is used to simulate the flow flied. As a result, the distribution of the velocity and the turbulent kinetic energy are obtained. Also, the changing tendency of the axial velocity and turbulent kinetic energy with pre-expansion pressure, pre-expansion temperature and the distance between nozzle exits are acquired. The result shows that the axial velocity and turbulent kinetic energy will go up with the increasement of the pre-expansion pressure and go down with the increasement of the distance between nozzle exits. With the pre-expansion temperature changing, the axial velocity and turbulent kinetic energy in the flow flied almost keep constant. In addition, Particle Image Velocimetry is used to test the multi-phase impact flow. The changing of the velocity and the turbulent kinetic energy are obtained. The result form experiment agrees with that from simulation well.COMSOL software is used to simulate the diffusion and solidification process of the coating agent in the host particle’s surface. FEM linked program is used to calculate the changing tendency of the coated layer thickness, the curvature change during diffusion process and the solid percentage during solidification process. The result shows that the speed before collision and eccentric degree will influent the above three parameters.A motion model is established for the host particle in the multiphase impact flow to study the strengthening mechanism of the flow transfer in the supercritical particle coated process. The particle residence time and particle through length was simulated. Three conditions including the condition of single stream of host particle from single nozzle (SP), particle group from single nozzle (SPG) and particle group from double nozzles (DPG) are chosen in this study, also, the pressure and the pre-expansion temperature as well as the distance between two opposite nozzles exits are defined as the different initial conditions. The changing tendency for the particle residence time and particle through length of the host particle was obtained.Finally, composite particle products, glass beads coated by paraffin wax, at different conditions are obtained through the coating experiment using supercritical fluid technology. Scanning electron microscope is used to characterize the morphology of the coated layer on the surface of the host particle. Using an analytic method to estimate the coated layer thickness, the changing tendency of the layer thickness with different operating conditions is obtained.