Coarse grained DEM simulation of non-spherical and poly-dispersed particles using Scaled-Up Particle (SUP) model

In this work, the validity of the Scaled-Up Particle (SUP) model, which is a novel coarse grain model for Discrete Element Method (DEM), is examined to simulate a flow of non-spherical and poly-dispersed particles. The SUP model is based on the authors’ previous work and the scaling law is derived from the continuum assumption of an arbitrary particles flow. We discuss that the model is applicable not only to spherical and mono-dispersed particles, as is the case tested in the previous work, but also to non-spherical and poly-dispersed particles. Simulations of various systems are performed such as compression of a particle bed, heap formation, high shear mixer, large scale rotary drum and V-mixer. It is shown that the results obtained from the SUP model are in both qualitative and quantitative agreement with those from the original particles as long as the resolution is sufficiently high.Washino K., Chan E.L., Nishida Y., et al. Coarse grained DEM simulation of non-spherical and poly-dispersed particles using Scaled-Up Particle (SUP) model. Powder Technology 426, 118676 (2023); https://doi.org/10.1016/j.powtec.2023.118676

Dem investigation of horizontal high shear mixer flow behaviour and implications for scale-up

In high shear granulation, various dimensionless or dimensioned parameter groups such as constant Froude number, tip speed, relative swept volume and specific energy input are commonly used as scale-up criteria, in order to maintain the powder bed internal flow or stress field across scales. One major challenge is obtaining the internal flow and stress field through experimentation given the lack of precise measurement techniques. Hence, this work employs DEM (discrete element method) simulations to study the internal flow patterns and behaviour of different scale batch, horizontal high shear mixers. The simulations provide a deeper understanding of the interaction of scale, impeller speed and fill level on the flow field, and show that the particle velocity is correlated with the relative swept volume in these mixers. It shows that the relative particle velocity is correlated, independent of scale, to the relative swept volume per rotation and highlights its values as a parameter for understanding and comparing mixer behaviour. The work also demonstrates the importance of the particle size chosen for the simulation as well as the tool-wall gap in the mixer, and highlights its importance as we interpret DEM results

Coupling non-local rheology and volume of fluid (VOF) method: a finite volume method (FVM) implementation

Additional to a behavior switching between solid-like and liquid-like, dense granular flows also present propagating grain size-dependent effects also called non-local effects. Such behaviors cannot be efficiently modeled by standard rheologies such as µ(I)-rheology but have to be dealt with advanced non-local models. Unfortunately, these models are still new and cannot be used easily nor be used for various configurations. We propose in this work a FVM implementation of the recently popular NGF model coupled with the VOF method in order to both make non-local modeling more accessible to everyone and suitable not only for single-phase flows but also for two-phase flows. The proposed implementation has the advantage to be extremely straightforward and to only require a supplementary stabilization loop compared to the theoretical equations. We then applied our new framework to both single and two-phase flows for validation

Coupling non-local rheology and volume of fluid (VOF) method: a finite volume method (FVM) implementation

Additional to a behavior switching between solid-like and liquid-like, dense granular flows also present propagating grain size-dependent effects also called non-local effects. Such behaviors cannot be efficiently modeled by standard rheologies such as µ(I)-rheology but have to be dealt with advanced non-local models. Unfortunately, these models are still new and cannot be used easily nor be used for various configurations. We propose in this work a FVM implementation of the recently popular NGF model coupled with the VOF method in order to both make non-local modeling more accessible to everyone and suitable not only for single-phase flows but also for two-phase flows. The proposed implementation has the advantage to be extremely straightforward and to only require a supplementary stabilization loop compared to the theoretical equations. We then applied our new framework to both single and two-phase flows for validation

Geometric similarity on interparticle force evaluation for scaled-up DEM particles

The scaled-up particle model, which is also commonly known as the coarse grain model or discrete parcel model, is frequently used to reduce the computational cost in Discrete Element Method (DEM). In the direct force scaling approach, the forces acting on original particles are first estimated and then directly scaled to apply to scaled-up particles. It is therefore crucial to appropriately evaluate the variables of the original particles, e.g. overlap and separation distance, from the scaled-up particles particularly when estimating complex interparticle forces. The present work proposes the use of geometric similarity for the evaluation of the original particle overlap and separation distance. It is demonstrated that the proposed method can provide an almost identical stress-strain curve between the original and scaled-up particles during uniaxial compression of a packed particle bed, whilst the conventional method in the literature gives significant overestimation of the stress. In addition, the scaled-up particles can reasonably replicate the original velocity distributions of cohesive particles with both liquid bridge and JKR surface adhesion forces in a dynamic flow system (vertical mixer). The simulation results suggest that the method proposed can be applied to any type of interparticle forces. A scaling of time step limit is also derived theoretically and discussed.Hu Y., Chan E.L., Tsuji T., et al. Geometric similarity on interparticle force evaluation for scaled-up DEM particles. Powder Technology, 404, 117483. https://doi.org/10.1016/j.powtec.2022.117483

Development of resolved CFD–DEM coupling model for three-phase flows with non-spherical particles

In this work, a resolved CFD–DEM coupling model for gas–liquid-solid three-phase flows with non-spherical particles is developed where the shape of the particle is implicitly captured by a superquadric function. Both gas–liquid and fluid–solid interfaces are smoothly represented with a specified thickness so that the interface thicknesses and CFD cell size are independent of each other. Several sensitivity studies are carried out and criteria for mesh- and thickness-independent results are proposed. It is confirmed that the proposed model can properly predict the hydrodynamic and capillary forces acting on particles with a wide range of shapes and contact angles. Finally, the model proposed is applied to perform several virtual experiments of typical chemical engineering processes: a liquid–solid fluidised bed and bubbly flow with various particle shapes. It is found that particle shape can have a significant impact on the fluid-particle interactions and resultant particle movement, leading to segregation and preferential alignment.K. Washino, E. L. Chan, T. Tsujimoto, et al. Development of resolved CFD–DEM coupling model for three-phase flows with non-spherical particles. Chemical Engineering Science 267, 118335 (2023); https://doi.org/10.1016/j.ces.2022.118335