A modified cohesion model for CFD-DEM simulations of fluidization

CFD-DEM simulations are performed to study gas-fluidization of particles with van der Waals force cohesion for both Group A and Group C particles. The particle spring constant used in such CFD-DEM simulations is commonly much smaller than that for realistic particles used in experiments. For cohesive particles, the predicted flow patterns depend on the value of particle spring stiffness used in the simulations. This dependence can be explained through a simple analysis involving head-on collision of two particles. A modified cohesion model is then proposed and verified through simulations of two-particle collisions. Simulations of gas-fluidization of cohesive particles with this modified cohesion model reveal that the predicted distributions of bubble size are insensitive to particle stiffness for Group A particles. For Group C particles, except for substantially small particle stiffness, the flow patterns are preserved when smaller particle stiffness is used. The proposed model, which was deduced through analysis of binary collisions, provides satisfactory results for fluidization of Group A particles manifesting only mild cohesion; however, similar to the previous finding by Kobayashi et al. [Powder Technol. 248, 143-152 (2013)] with a simpler model, it is less accurate for Group C particles with strong cohesive interactions, where large agglomerates form.