Effects of scaling criteria on modelling of multi-phase flow in the packed bed using coarse grain CFD-DEM

Abstract

The numerical modelling with computational fluid dynamics coupled with discrete element method (CFD-DEM) could be of high fidelity but rather time consuming, which leads to the development of coarse grain DEM (CFD-CGDEM). This paper describes the effects of scaling criteria for CFD-CGDEM on the modelling of multi-phase flow in packed bed. Four representative scaling criteria for particles contact interaction are discussed to analyze the packing structure and pressure drop and compare the relative deviation between CFD-CGDEM and CFD-DEM. It is found that when the spring constant in CFD-CGDEM is enlarged by α3 or α2 times or remains the same as that in original CFD-DEM, as α is defined as coarsen degree which is referred as the ratio between parcel size and particle size, a relatively large spring constant should be chosen to maintain the similar porosity and pressure drop. However, when the spring constant in CFD-CGDEM was scaled moderately by α times, the modelling results of CFD-CGDEM are comparable to data from CFD-DEM regardless of the value of spring constant. Furthermore, a quantitative analysis shows that the relative deviation in porosity and pressure drop between CFD-DEM and CFD-CGDEM will be enhanced as coarsen degree increases but the variation is insignificant with domain size for periodic boundary. The increase of parcel size could affect the simulation of porosity in packed bed and deviate the predicted hydrodynamics away from the CFD-DEM. In addition, the comparison of computational efficiency illustrates the speed up of CFD-CGDEM increases with the coarsen degree while the relative deviation also increases. This study provides instructive guidance for the application of CFD-CGDEM to model the multiphase flow in packed beds.