^{1}, Susannah Balson

^{1}, Yuqing Feng

^{1}, Peter Witt

^{1},

Phil Schwarz

^{1}and Aibing Yu

^{2}

^{1}Fluid Process Modelling, CSIRO Mathematics, Informatics and Statistics, Australia

^{2}School of Materials Science and Engineering, University of New South Wales, Australia

Solid mixing and segregation are complex phenomena in a gas fluidized bed when particles of different size and/or density exist. Despite being an intensive research area, because of so many pertinent factors, such as size ratio, density ratio, operation velocity, bed aspect ratio and even gas distributor design, there are no general design rules or predictive models that can reliably predict the performance.

Over the past two decades, complex gas-solid flow systems have been extensively studied using either two fluid mode (TFM) or coupled used discrete element method (DEM) and Computational fluid dynamics (CFD) model, well known as DEM-CFD model. So far, there is no problem in modelling mono-sized system, as the fluid drag force, which is the main particle-fluid interaction force, can be reasonably described using empirical correlations.

The equation to calculate the drag force for different sized particles in a particle mixture is not so well established. The lack of an effective way to describe drag force at particle scale prevents a better understanding of the underlying mechanism governing multi-sized systems. Early research simply use the one extended from mono-sized particles. Recently, there are attempts to modify the equation in the literature using lattice-boltsman model or large eddy simulation, but the results are still very preliminary.

This paper presents a detailed CFD modelling of flow dynamics in a multi-sized particle system using an advanced CFD software package (ANSYS CFX) . Following model validation using single particle and mono-sized particle system, the drag force over individual particles in a bi-sized system have been calculated. Through parametric study of different bi-sized systems, a better correlation to describe fluid drag force for multi-sized systems has been obtained.