Role of DEM in Assessment of Continuum Equations for Solid–Solid Drag Force with Various Particle Size Ratios

Abstract

Many industrial processes in circulating fluidized beds (CFB) include different solid phases which can have different properties and sizes. For instance, the combustion of biomass particles fluidized by air in a CFB containing sand particles as the inert fluidized particles is one of the processes absorbed a great deal of attention in computer simulations. However, the large size ratios between the sand particles (~0.3 mm) and the biomass particles (1–10 mm) can critically question the applicability of continuum equations such as Syamlal’s formula to evaluate the solid–solid drag forces used in Eulerian simulations. In this paper, we employ DEM simulations to find out how the two solid phases with large size ratios between their particles interact. We quantify the volumetric drag force and compare it to the Syamlal’s formula. The main problem with the latter is associated with the inhomogeneity that the size difference imposes locally, which is against the assumption of homogeneous phases in the derivation of the formula. This can create a way to modify the existing drag models based on DEM simulations.