Numerical Simulations of Fluidized Suspensions of Cohesive Particles with Size Distributions

Euler-Lagrange simulations of fluidized beds, where the locally-averaged equations of motion for the fluid phase is solved in an Eulerian framework and the particles are tracked in a Lagrangian fashion, have found widespread use in the study of fluidization [1-4]. This approach is commonly referred to as CFD (computational fluid dynamics)-DEM (discrete element method) when all the particles are followed and as CFD-DPM (discrete parcel method) or MP-PIC (multiphase particle-in-cell) when only a small number of representative particles (a.k.a. “parcels”) are simulated [3,4]. Many research groups are currently investigating the effects of cohesion and size distribution on fluidization characteristics via CFD-DEM simulations [for example, see ref. 1, 2].

We have performed CFD-DEM simulations of gas-fluidization of Geldart Group A particles in small periodic domains in order to probe the fluidization characteristics of gas-fluidized suspensions at volume fractions typically observed in circulating fluidized beds and turbulent fluidized beds. In this poster, we will present results related to the following three questions: (a) How does the inclusion of cohesion alter the fluidization of monodisperse particles? (b) How does the addition of fines affect fluidization when cohesion is not considered? (c) What is the combined effect of fines and cohesion?We also ask how one should systematically coarse-grain the results of such detailed CFD-DEM simulations to obtain effective constitutive models (for example, for the fluid-particle interaction force) that are needed for affordable simulations of industrial scale beds, which entails coarse fluid grids as well simulation of only a small number of representative particles. As shown previously [5,6], when such coarse-graining is done, the drag coefficients must be corrected. We will demonstrate in this poster that both coarsening the fluid grid and switching from DEM to DPM lead to lower effective drag coefficients.