MacroPac from Intelligensys - particle size segregation studies

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Particle Size Segregation with MacroPac: A Cereal Story

Some years ago, a paper by Rosato et al¹ (memorable not least because of its title) suggested a Monte Carlo approach for simulating segregation of particles of different sizes. The particles are all raised to the top of the simulation box, and allowed to fall. The smaller particles fall more freely, so the larger particles gradually rise up through the bed. This simulates vigorous shaking of the box, i.e. high amplitude, low frequency shaking.

MacroPac includes these segregation methods, and lets you look at non-spherical particles with different densities. Some of the 'cereal' examples below illustrate some simple studies.

In all cases, the protocol adopted was to

(a) pack the box with 'static' packing

(b) settle the particles in the z direction

Example 1. Two different plate sizes: "breakfast cereal"

Plate 1 'wheatflakes' of monodisperse size = 4x4x1 density = 1

Plate 2 'cornflakes' of monodisperse size = 8x8x1 density = 1

These are packed 50:50 by volume, into a box that is 30x20x60 units in size, with hard walls in all directions.

These pictures show the static-packed box, the box following initial settling, and the box once the 5 'drops' have taken place. Clearly, the large particles have segregated to the top.

Example 2. Mixed spheres and plates: "Muesli"

The second example represents a 'muesli' mix, with raisins, brazil nuts and cereal flakes. Like Rosato et al, we have used spherical brazil nuts.

Sphere 1 'brazils' diameter=5 density=1.5

Sphere 2 'raisins' diameter=2 density=2.0

Plate 'cerealflakes size = 3x3x1 density=1.0

The volume ratio of was chosen to be 20:5:75, fairly similar to your average luxury muesli. The simulation box has hard walls in all directions, and is 30x10x100 units in size.

The results for the box after 'static packing', setting with no drops, and after 5 drops, are shown below.

The brazil nuts have clearly risen to the top, despite the fact of their higher density. More detailed studies show that shape is more important than density in determining segregation characteristics.