CFD-DEM study on mixing characteristics of ZrO2 particles using the fluidized bed-chemical vapor deposition method

Fluidized bed-chemical vapor deposition (FB-CVD) is the key method to prepare low-temperature isotropic py-rolytic carbon (LTIC) for artificial heart valve. In the process of FB-CVD of pyrolytic carbon, ZrO2 hollow particles are not only the bed particles forming the fluidized bed, but also play the role of heat carrier in the pyrolysis reaction of carbon source gas. The mixing degree of particles directly affects the coating quality of pyrolytic carbon. In this paper, a coarse-grained CFD-DEM model is used to conduct 3D numerical simulation of fluidized bed to investigate the effect of fluidization wind speed on the mixing characteristics (particle distribution, particle motion and Lacey index) of ZrO2 hollow particles from the particle perspective. The results show that the mixing process can be accelerated by increasing the fluidization wind speed within a reasonable range, and radial mixing is more sensitive to fluidization wind speed than axial mixing. In addition, due to the different densities of particles in the furnace along the radial direction, the number of particle collisions and the influence of traction also differ greatly, resulting in more significant changes of particle velocity in the fountain area, while the ve-locity distribution in the annular gap area near the wall is relatively smooth.