Incorporating Roughness Measurements in DEM Simulations of Cohesive Particle Fluidization

Fine particles exhibit complex flow patterns due to the strong interparticle cohesion and a reliable method to predict the fluidization behaviors for fine particles remains absent. The Discrete Element Method (DEM) based simulations, which help bridge the experimental and theoretical approaches, may aid in formulating a general continuum theory for fluidization of fine particles. Cohesion can be easily incorporated in DEM in order to simulate fine particles. However, the providing a correct form of a cohesion model is more difficult. Though it is well known that cohesion is affected by surface roughness, input parameters in cohesion models were often ad hoc selected and validation of simulations results via experiments is rarely conducted. In this work, DEM simulations were performed to study the fine particles in a gas-fluidized bed. A stochastic approach was developed to incorporate the surface coverage of asperities in DEM. Using the size and coverage of asperities measured from the analysis of Scanning Electron Microscopy (SEM) images of particle surface, DEM with a cohesion model based on the Rumpf model, successfully reproduced the experimental results in terms of fluidization curves. Assuming a smooth surface of particles would otherwise lead to considerable overestimation of minimum fluidization velocity. Simulations of fine particles in a periodic riser were also conducted with the properties of particle agglomerates collected. It is found that agglomerates reduced with increasing coverage of asperity. The results highlight the necessity of incorporating surface asperities in DEM to obtain consistent results with experiments.