Particle Adhesion Effects on Particle Size Distribution of Titania Nanoparticle Agglomerates in a Conical Fluidized Bed: A Computational Fluid Dynamics and Discrete Element Method Adhesive Approach

The fluidization characteristics of nanoparticle (NP) agglomerates are affected by the particle size distribution (PSD), with PSD depending on the particle interaction force and adhesion effects. In this study, the impact of adhesion force and surface cohesiveness on the minimum fluidization velocity (U-mf) and PSD of titania NP agglomerates was studied numerically in a conical fluidized bed by applying the computational fluid dynamics-discrete element method approach. Experimental studies were carried out to identify the effect of the bed inventory, the ratio of the static bed height to the inlet column diameter (h(0)/d(i)), and airflow velocity on PSD. The experimental results showed that the fraction of simple-agglomerates increases by increasing the fluidization time, while the number of complex-agglomerates increases by increasing h(0)/d(i). The numerical results were validated by the experimental findings, and they allowed evaluation of the effects of h(0)/d(i) and contact models on U-mf, and the impact of contact models and flow regimes on PSD profiles. The results indicated that using elastic contact models (Hertz-Mindlin theory coupled with the Johnson-Kendall-Roberts model) led to more accurate data than the inelastic models when predicting U-mf and PSD at different h(0)/d(i) ratios. In addition, the uncertainty in the prediction of U-mf increases by increasing h(0)/d(i). The bed homogeneity and its packing structure were dependent on the particle surface cohesiveness in the range of 10(-22) to 10(-21) J and van der Waals Bond numbers below 20, as they enhance the continuous formation and breakage of NP agglomerates. The PSD profiles of titania particles followed a Gaussian-type curve by considering high surface cohesiveness and cohesive force.