Systematic Evaluation and Development of Discrete Element Coarse- Graining Approaches for the Modeling of Fluidized Particle Systems

• Applicants: Professor Dr.-Ing. Matthias Kraume; Professor Dr.-Ing. Harald Kruggel-Emden
• Subject Area: Mechanical Process Engineering
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 456827728

The coupling of Computational Fluid Dynamics (CFD) and a Coarse- Grained Discrete Element Method (CFD-CGDEM) is a relatively new and efficient numerical method for the simulation of particulate systems. Based on the Discrete Element Method (DEM) a chosen number of particles is combined into one representative parcel. This reduces the number of particles that need to be tracked significantly and leads to an enormous speed-up. Therefore, it is a promising method for the simulation of particulate systems on an industrial scale. Like in classical DEM the trajectories of each parcel are calculated by solving Newton’s law of motion and appropriate models are used to describe contact and fluid-particle interactions. Due to the conservation of energy or based on similarity theory the particle- particle, particle-wall, and particle-fluid interaction forces need to be scaled. In the last years, several scaling approaches by numerous authors were proposed, but a systematic comparison of those approaches has yet not been done. The requested project will start with a fundamental and systematic comparison of different scaling approaches. Aim is to find the scaling approach that gives reliable results over a wide range of scaling factors. Preliminary studies have shown that the ratio of characteristic reactor length to parcel diameter should not exceed a certain limit. An adaptive Coarse-Graining- Method will be developed to allow different scaling factors for narrow and wide regions within the reactor. It will be investigated if this approach allows CFD-CGDEM to be efficiently used for reactors with closely packed internals which are especially relevant in possible technical applications. An original CFD-DEM requirement is that the cells are bigger than the particles. Therefore, Coarse-Graining leads to an inherent coarsening of the mesh. That is why important meso-scale effects (e.g., cluster formation) cannot be resolved. It will be investigated if methods that override this cell size requirement lead to a higher accuracy of CFD-CGDEM. Furthermore, it will be examined if a modelling of meso-scale effects using filtered drag models has a positive effect on the quality of the results. By now only few and very basic studies have been done on the usability of CFD-CGDEM for poly-disperse particulate systems. The important aspect of a correct prediction of particle segregation has not yet been investigated. Aim of the project is to close this gap and to evaluate if CFD-CGDEM can in principle be used to predict the segregation behavior of bi- dispersed particulate systems. Based on the developed methods CFD-CGDEM will be used for the simulation of an industrially relevant case including internals. Mono- and bi-dispersed systems will be investi-gated. Aim is to prove that CFD-CGDEM is an efficient and reliable method for the simulation of particulate systems for “real world”-applications as well as to identify application limits.

• DFG Programme: Research Grants