Numerical Simulations of Flow Behaviour of Agglomerates of Nano-Size Particles in Bubbling and Spouted Beds with an Agglomerate-Based Approach

Abstract Numerical simulations are performed on the behaviour of agglomerates of nanoparticles in bubbling gas fluidized beds and spouted beds—systems that are widely used in handling and processing particulate solids in various industrial sectors including biomaterials, foods and pharmaceuticals. An Eulerian two-fluid approach is used and the cohesive force between particles is considered. An empirical expression for the solids pressure of agglomerates is used (Jung and Gidaspow, 2002). The interaction between gas and agglomerates is considered with an agglomerate-based approach. Simulated results show that the fluidized bed has a very high expansion ratio with no distinct bubbles in the bubbling fluidized bed. In the spouted bed, however, the concentration of agglomerates is nearly homogeneous in both the dilute and transitional zones. The velocity of agglomerates is found to be higher than that in the annulus region, whereas the concentration distribution shows an opposite trend with a nearly closing packing of agglomerates in the annulus region. A high spouting gas velocity is shown to be required to fluidize agglomerates in the spouted bed. Comparisons of the modelling results are also made with limited experimental results.

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