Investigation of Void Fraction Schemes for Use with CFD-DEM Simulations of Fluidized Beds

Abstract

This paper investigates the spatial resolution of computational fluid dynamics-discrete element method (CFD-DEM) simulations of a bubbling fluidized bed for seven different void fraction schemes. Fluid grids with cell sizes of 3.5, 1.6 and 1.3 particle diameters were compared. The particle velocity maps from all of the void fraction schemes were in good qualitative agreement with the experimental data collected using magnetic resonance imaging (MRI). Refining the fluid grid improved the quantitative agreement due to a more accurate representation of flow near the gas distributor. The approach proposed by Khawaja et al. (J. Comput. Multiphase Flows, 2012, 4, 183-192) provided the closest match to the exact void fraction though only the particle centered method differed significantly. These results indicate that the fluid grid used for CFD-DEM simulations must be sufficiently fine to represent the inlet flow realistically, and that a void fraction scheme such as that proposed by Khawaja be used.

Comparative analysis of porosity coarse-graining techniques for discrete element simulations of dense particulate systems

“…2d), assuming that the boundaries are straight and the particles are cut in slices. Satellite point methods (SPM) [17][18][19][20][21][22][23] approximate the particle as collection of smaller pseudo-particles. Porosity is then determined by the amount of these pseudo-particles within each cell.…”

“…Additionally, the smoothness of solution in small cells is stated. Particle meshing method (PPM) [18] Satellite point methods [17,[19][20][21][22][23][24][25][26][27] Exact methods* Difficult Moderate Difficult Yes (if Δx>~2dp) Easy…”

Study of filtered interphase heat transfer using highly resolved CFD–DEM simulations

“…The equations for the gas and particle phases are coupled by the momentum exchange term S p in Equation ) and the porosity ϕ g in Equations ) and (). The particle phase properties are mapped to the Eulerian cell by a method similar to the satellite point method, 45 which disperses a particle into a series of randomly distributed pseudo‐particles. The porosity of the cell can be obtained by the number of pseudo‐particles located in.…”

Positron Emission Particle Tracking for Liquid‐Solid Mixing in Stirred Tanks

“…The Euler-Lagrange approach, which allows the particulate phase to be directly modeled, does allow a direct determination of the N js , and also avoids issues regarding the continuum modeling of discrete particles. A major disadvantage of this methodology, however, is that it is extremely computationally expensive [41], especially in the case of two-way coupling and finely resolved flow, thus limiting its suitability for simulating large, industrial-scale systems. Nonetheless, as algorithms become more efficient and hardware more powerful, Euler-Lagrange methodologies are expected to prove increasingly valuable in the coming years and decades [42].…”