Numerical investigation of fluidization behaviors of nanoparticle agglomerates with improved drag models using the DDPM approach

The nanoparticle agglomerates fluidization exhibits multiscale heterogeneous flow structures, while there is yet no suitable drag models developed to account for the effects of heterogeneous flow structures for nanoparticle agglomerate fluidization. In this study, the effects of drag correction and drag models on the fluidization characteristics of nanoparticle agglomerates in the bubbling and turbulent fluidization are studied using the DDPM approach. The bed expansion behaviors, solid distributions, solid circulation, and the pressure fluctuation are analyzed. Results show that the original Gidaspow drag model over-predicts the bed expansion height in the bubbling fluidization, and the revised Gidaspow drag model or the EMMS drag model resolves reasonable bed expansion height and the stratification of solids concentration. The drag correction yields negligible differences in bed height and flow field between the revised and original Gidaspow drag models in the turbulent fluidization. The revised Gidaspow drag model or the EMMS drag model simulates stronger heterogeneous structures than those of the original Gidaspow drag model. The power spectral density increases then decreases with increasing fluidization velocity and increases with decreasing drag correction coefficient. The sub-signal energy distribution varies similarly. Macro-scale signals exhibit no evident trends, while meso and micro-scale structures are most sensitive to the variation of the fluidization velocity and the drag correction.