This study concerns the dynamic of particle-particle collision characteristics in a three-dimensional gas-solid tapered fluidized bed. To this aim, a two-way coupled discrete element method and computational fluid dynamics is used to obtain the position and velocity of particles in the bed. By post-processing of data, the collision characteristics such as the collision frequency, relative collision velocity, and contact time of colliding particles are calculated. Next, the effect of inlet air velocity ( on the particulate flow dynamics and collision characteristics is studied statistically. Predictive equations for collision parameters are obtained in terms of the dimensionless using the regression analysis. Furthermore, it is shown that the relative collision velocity has a Log-normal distribution and its parameters are computed in time. Additionally, the collision characteristics are calculated and analyzed in the different zones of the bed. The results indicate that no collision occurs at heights upper than 350mm for v_inlet up to 6.8 times the minimum fluidization velocity. Finally, the particle-particle collision frequencies are compared with the Martin and Gidaspow models where, on average, the minimum differences at v_inlet=2.2m/s as 29.7 and 22.6 and the maximum ones at v_inlet=0.7m/s as 48.1 and 22.6, respectively.
