Pore Structure of the Packing of Fine Particles
28 August 2007
Fine particles are important to many industries, including mineral, materials, pharmaceutical and chemical industries. For those particles, the adhesion force, of which the van der Waals force is often the most important, plays a dominant role. Therefore, fine particles show quite different bulk behaviour from that of coarse particles in packing process.
Fig. 1. Pore connectivity in a spherical sample taken from the packings of 10μm particles.
Our work presents a numerical study of the pore structure of fine particles. By means of discrete element method simulation, packings of mono-sized particles ranging from 1 to 1000 µm are constructed. Our results show that packing density decreases with decreasing particle size due to the effect of the cohesive van der Waals force. Pores and their connectivity are analysed in terms of Delaunay tessellation. Figure 1 shows the connection of the Delaunay cells in a spherical sample taken from 10 µm particle packing, indicating very complicated connections among the cells. The geometries of the pores are then represented by the size and shape of Delaunay cells and quantified as a function of packing density or particle size. With decreasing particle size or packing density, the pore and throat sizes as well as their variation increase (Figs. 2 and 3). It shows that the cell size decreases and the cell shape becomes more spherical with increasing packing density. A general correlation exists between the size and shape of cells: the larger the cell size relative to particle size, the more spherical the cell shape. This correlation, however, becomes weaker as packing density decreases. The connectivity between pores is represented by throat size and channel length. With decreasing packing density, the throat size increases and the channel length decreases.
The pore scale information would be useful to understand and model the transport and mechanical properties of porous media.
Fig. 2. Distribution of equivalent volume diameter of Delaunay cells for different packing densities
Fig. 3. Joint distribution of effective throat diameter and channel length for 10μm particle packing
This research was published in J. Colloid Interface Sci., 299, 719-725 (2006).