A two-scale approach for the simulation of multi-dimensional separation of fine particle systems
Matthias Franzreb, Mathias Krause, Hermann Nirschl
Sub-project of SPP 2045
The separation of fine particles suffers from a decline in selectivity and throughput for systems of particles of size between 100nm and 10µm. While for larger particles inertial forces dominate, what allows the use of cyclones, smaller particles can be separated by diffusion separators, taking advantage of interaction forces. In the transition region none of these forces dominate. For a model describing the particle dynamic, however, these forces cannot be neglected. Therefore, the connection of different separation parameters have to be considered in order to develop new and improve existing processes. The main objective of this research proposal is the clarification of the behaviour of particle suspensions in the mentioned critical size range by consideration of different separation features for a multidimensional fractionation. Here, in particular the influence of the flow, the particle shape and the solid volume fraction is to be examined. Currently neither suitable models nor efficient simulation tools are available for this task. Hereby, the main difficulty one faces is the consideration of a large number of arbitrary shaped particles, due to tremendous required computational resources. Therefore, suitable numerical investigations have not been performed yet. This gap can be overcome by applying a new parallel algorithm, based on an innovative two-scale model, which considers the dynamic of a realistic suspension with a distribution of different shape parameters. First, the distribution of this parameters, i.e. aspect ratio and elongation, is to be investigated with advanced measurement technology (i.e. CT, SAXS, SEM, etc.). Then, for the simulation of volume resolved particles the Homogenised Lattice Boltzmann Method is applied. It fits for this specific task since it is good parallelisable and contains an intrinsic lubrication force, which allows to omit additional collision models. This allows the simulation of a large number (>1000) of arbitrary shaped particles and thereby the examination of sensitivities of the selectivity regarding shape parameters, contact behaviour and volume fraction. For the simulation of industrial relevant quantities, finally an advection-diffusion equation is utilized, which displays the particles as concentrations. Hereby, the model as well as the implementation has to be modified to account for anisotropic effects which originate form a non-spherical particle shape. This is done based on results gained in the simulations of volume-resolved particles by a mesoscopic modelling including anisotropic forces and an isotropic diffusion-like coefficient. At the end of the project, there are insights, a model and a simulation tool for the prediction of the dynamics of arbitrary shaped particles on a volume resolved micro-scale as well as on a macro-scale, to allow for the prediction of the influence of process machines.