Particle flow characteristics in a gas–solid fluidized bed: a microscopic perspective by coupled CFD–DEM approach

In a dense gas–solid fluidized bed, the microscopic quantities, including forces and energy of particles, directly determine their macroscopic motion in space. In this work, the CFD–DEM coupling approach is used to detect the energy evolution and the effect of fluid forces on the particles using a microscopic perspective. The numerical simulation accuracy of CFD–DEM to predict the macroscopic motion behavior of the particles was validated by carrying out high-speed photographic tests. The results showed that the drag force positively correlates with the inlet flow rate and particle diameter, where it exists only near the inlet. In the axial position of the fluidized bed near the inlet, the tangential contact force is significantly dominant, while an effect of a small proportion of particles with a normal contact force (> 0.1N) is founded. Under different operating conditions, the fluid pressure gradient force can be neglected at a position greater than two times the inlet length where a convex curve shape is formed. In addition, the particle energy is positively correlated with the inlet flow rate and the particle diameter, where the existing bubble formation causes energy fluctuations. This study reveals the microscopic mechanism of gas–solid interaction and provides theoretical guidance for the optimal design of fluidized bed structure and improvement of mathematical models.