LBM-IBM-DEM modelling of magnetic particles in a fluid

Simulation of a bidisperse magnetorheological fluid using the combination of a two-component lattice Boltzmann method and a discrete element approach

In this study, a two-component lattice Boltzmann method (TLBM) in combination with a discrete element approach (DEA) based on a representative volume element (RVE) with respect to a bidisperse magnetorheological fluid (MRF) was performed to simulate the behavior and microstructure formation of magnetic particles in a carrier liquid. The bidisperse MRF reported herein is a suspension dispersed by soft micron carbonyl iron (CI) particles and Fe₃O₄ nanoparticles dual-coated with gelatin and multi-walled carbon nanotubes (MWCNTs) in the carrier liquid. In the TLBM of two-component liquid and particle simulation, the inter-particle interactions were completely ignored; on the other hand, the DEA was just employed for calculating the dynamic behavior of particles. Therefore, due to the explicit nature of the combination of TLBM and DEA, it is a more efficient and accurate strategy for the simulation and calculation of complex MRF systems. Moreover, the immersed boundary method (IBM) was used to describe the interactions between the magnetic particles and the carrier liquid. The RVE of the bidisperse MRF was selected to eliminate specific operational conditions and reduce the calculation costs. New numerical results were obtained for the motion velocities, microstructure evolution and kinetic energy of bidisperse magnetic particles (BMPs) under the effect of a magnetic field; when the mass fraction of the nanoparticles was 0.1, the bidisperse MRF exhibited an improved response time in terms of the particle motion and microstructure formation. In addition, the effects of the Reynolds (Re) and Hartmann (Ha) numbers on the fluid-particle interaction and flow velocity were illustrated.

Influence of Shell Thickness on the Colloidal Stability of Magnetic Core-Shell Particle Suspensions

We present a Discrete Element study of the behavior of magnetic core-shell particles in which the properties of the core and the shell are explicitly defined. Particle cores were considered to be made of pure iron and thus possessed ferromagnetic properties, while particle shells were considered to be made of silica. Core sizes ranged between 0.5 and 4.0 μm with the actual particle size of the core-shell particles in the range between 0.6 and 21 μm. The magnetic cores were considered to have a magnetization of one tenth of the saturation magnetization of iron. This study aimed to understand how the thickness of the shell hinders the formation of particle chains. Chain formation was studied with different shell thicknesses and particle sizes in the presence and absence of an electrical double layer force in order to investigate the effect of surface charge density on the magnetic core-shell particle interactions. For core sizes of 0.5 and 4.0 μm the relative shell thicknesses needed to hinder the aggregation process were approximately 0.4 and 0.6 respectively, indicating that larger core sizes are detrimental to be used in applications in which no flocculation is needed. In addition, the presence of an electrical double layer, for values of surface charge density of less than 20 mC/m², could stop the contact between particles without hindering their vertical alignment. Only when the shell thickness was considerably larger, was the electrical double layer able to contribute to the full disruption of the magnetic flocculation process.