Effective Drag on Spheres, Rods, and Discs Immersed in a Fluidized Bed at Minimum Fluidization - Measurements and Modeling Work

With their excellent mass, momentum, and heat transfer properties gas-solid fluidized beds (FB) are used in a variety of applications, involving the presence of larger particles immersed in beds of smaller bulk solids (e.g., fuel particles in a sand/ash bed). It is known that the interaction between the large particles and the emulsion of bed material impacts the bed-to-particle mass and heat transfer rate, thus, the particle conversion. However, currently there is not a complete theory of the momentum exchange between the large particles and the emulsion of bulk solids, due to the complexity of the rheological behavior of the latter. Such information is vital for the development of reliable descriptions of the mixing mechanisms that the large particles exhibit in the bed, so that the design and scale-up of FB processes could be done more precisely.

Based on the hypothesis that gas-solid FBs (of Geldart-B-type particles) feature a non-Newtonian rheological behavior, the authors of this work have previously developed an experimental methodology to study the momentum exchange between immersed objects and gas-solids emulsions at minimum fluidization. By means of falling object experiments with magnetic particle tracking the instantaneous velocity can be measured, which allows the assessment of the shear stress on the immersed objects, and consequently the analysis of the rheological behavior of the emulsion.

Taking departure in the findings from the works done with spherical objects (of varying size and density) in fluidized emulsions of various bulk solids (of varying size, shape, and density) the present work aims to synthesize the current understanding and, through experimental data, extend it to non-spherical objects (rods and discs). Additionally, initial computational fluid dynamics (CFD) simulations are performed and compared with experimental results to evaluate the suitability of available numerical models. Based on this comparison, need for possible model development is discussed.