Influence of restitution and friction coefficients on the velocity field of polydisperse TiO2 agglomerates in a conical fluidized bed by the adhesive CFD-DEM simulation

Could the Rebound Characteristics of Oblique Impact for SiO2 Particles Represent the Ash Particles?

Collisions between particles or with a surface have been widely applied, in which the restitution coefficients are the important parameter to describe the particle rebound behavior. SiO2 particles are often used instead of ash particles in theoretical analyses; however, whether this is justifiable has not been confirmed. This paper compares the rebound characteristics of oblique impact for SiO2 particles and ash particles by experimental and theoretical analyses. Based on the rigid-body theory, the tangential restitution coefficients, rebound angle-particle center, and reflection angle-contact path predicted by SiO2 particles are basically in agreement with the experimental results for ash particles, especially at large impact angles. However, there is a slight error at 2.2 m/s as the velocity approaches the critical capture velocity.

Computational analysis of the particle size effect on the pressure profiles and type of flow regimes of TiO2 microparticles in a fluidized bed

The effect of particle size on the pressure profiles and flow regimes of the bed containing TiO2 microparticles (MPs) was investigated in a fluidized bed. The fluidization behavior of particles with mean diameters, d p , of 170, 200, 225, and 300 μm at different gas velocities, U g , was investigated both experimental and computational viewpoints. A computational fluid dynamic (CFD) model was developed by the Eulerian–Eulerian approach to evaluate the sensitivity of the Syamlal–O’Brien, and Gidaspow drag models on the predicted results of the bed pressure profiles. The results showed that with increasing particle size, the amplitude of pressure fluctuations increases and the type of flow regime in the bed tended from bubbling to slugging flow regime. The error analysis showed that the use of the Gidaspow model led to more accurate results than the Syamlal–O’Brien model in predicting the bed pressure drop and pressure fluctuations in the slugging flow regime. However, the Syamlal–O’Brien model was more suitable for predicting the pressure profiles in the bubbling flow regime. The results were more suitable for the bed containing particles of 300 μm than the beds with d p  ≤ 225 μm. The highest and lowest deviations between the experimental data and simulation outputs were obtained at U g of 0.295 and 0.650 m/s, respectively. The findings confirmed that the mutual effects existed between the d p pressure profiles, and the type of flow regimes in the bed.