Most industrial end and intermediate products are solid materials in particle form. Particulate systems exhibit unique feature which is a combination of solid, liquid and gases because they can undergo certain deformation, they can be made to flow and they are also compressible. Most particulate systems interact with fluid phases since the pores within and between particles are filled either by gas or liquid. The fundamental understanding of particulate systems is largely incomplete due to the lack of means for observation and measurement. Mathematical modelling and computer simulations are used to assist understanding these systems and predicting their behaviour. Various modelling and simulation methods have been developed and adopted in particle technology field, which exhibits a trend from macro-scale to micro-scale and multi-scale modelling, from continuum body approach to discrete element approach, from empirical to physically-based and from analytical to numerical solutions. Amongst many modelling methods used for particulate systems, Discrete Element Method (DEM) represents a powerful and prominent tool. In DEM each particle is treated individually in terms of the physical properties, reactions to the external forces and the motions that result. In this manner, DEM preserves the unique features of particle assemblages in contrast to many other approaches which either assume the system as a continuum body or require significant simplifications regarding the stochastic nature of the systems being examined.
This dissertation has covered the topics of modelling and simulations of particle packing, packing compression and interaction between a (static and dynamically evolving) particle packing and fluid flow through it. Its particular focus is the application of DEM to packed bed systems, in contrast to the more general developments in the literature which concentrate on fluidised or particle transport systems.
In order to generate an initial stochastic packed bed of particles, use is made of the rain model, Monte Carlo method and central growth model. A compression model for regular particle packings is proposed and demonstrated to be an effective method. To realistically simulate large deformation of particle packing under compression, the combination of DEM with Finite Element Method (FEM) is required. These tools form a basis from which applications are developed.
The main focus of the dissertation is on the exploration of applications, benefits and current limitations of DEM in assisting further understanding and prediction of particulate system behaviour, through three case studies: axial porosity distribution in a packing of deformable particles under compression (with the implication of caking problem); packing compression induced by fluid drag force (applicable to Cake Filtration and Chromatography); granule flow and fluid flow maldistribution in a moving bed.
The results obtained from the simulations are consistent with experimental results and expectations based on accumulated general experience of these systems as reported in the literature. DEM is demonstrated to be a powerful modelling and simulation means for conducting research upon particulate systems because of the simple, realistic approach and the magnified information database generated from the simulations which cannot be matched in physical experiments.