A Dynamic Coarse Grain Discrete Element Method for Gas-Solid Fluidized Beds by Considering Particle-Group Crushing and Polymerization

Xiaodong Wang,Kai Chen,Jie Ouyang,Ting Kang

doi:10.3390/app10061943

Abstract

The discrete element method (DEM) coupled with computational fluid dynamics (CFD) is used extensively for the numerical simulation of gas-solid fluidized beds. In order to improve the efficiency of this approach, a coarse grain model of the DEM was proposed in the literature. In this model, a group of original particles are treated as a large-sized particle based on the initial particle distribution, and during the whole simulation process the number and components of these particle-groups remain unchanged. However, collisions between particles can lead to frequent crushing and polymerization of particle-groups. This fact has typically been ignored, so the purpose of this paper is to rationalize the coarse grain DEM-CFD model by considering the dynamic particle-group crushing and polymerization. In particular, the effective size of each particle-group is measured by a quantity called equivalent particle-group diameter, whose definition references the equivalent cluster diameter used by the energy-minimization multi-scale (EMMS) model. Then a particle-group crushing criterion is presented based on the mismatch between the equivalent diameter and actual diameter of a particle-group. As to the polymerization of two colliding particle-groups, their velocity difference after collision is chosen as a criterion. Moreover, considering the flow heterogeneity induced by the particle cluster formation, the EMMS drag force model is adopted in this work. Simulations are carried out by using a finite volume method (FVM) with non-staggered grids. For decoupling the Navier-Stokes equations, the semi-implicit method for pressure linked equations revised (SIMPLER) algorithm is used. The simulation results show that the proposed dynamic coarse grain DEM-CFD method has better performance than the original one.

Highlights

Inside a gas-solid fluidized bed, particles driven by a gas flow exhibit complex and intriguing flow patterns
To be able to model a gas-solid fluidized bed, the discrete element method (DEM) is coupled with computational fluid dynamics (CFD) to set up a DEM-CFD
The PCPM is capable of showing the presence of multiple bubbles in the bed compared to the TM. These results indicate that the PCPM is better that the TM in describing the heterogeneity of the particle distribution in the fluidized bed

Summary

Introduction

Inside a gas-solid fluidized bed, particles driven by a gas flow exhibit complex and intriguing flow patterns. The mutual interaction between the discrete particles and continuum gas brings desirable features for many industrial applications, which include rapid heat and mass transfer, good mixing of solids and fast chemical reaction [1,2,3]. Over the past few decades, many attempts have been made to model the complex gas-solid flow behavior in fluidized beds [4,5,6,7]. The discrete element method (DEM) which was first described by Cundall and Strack [8] is one of the most used simulation tools for dense granular flows [9,10]. To be able to model a gas-solid fluidized bed, the DEM is coupled with computational fluid dynamics (CFD) to set up a DEM-CFD

Objectives

Results

Conclusion