Effect of particle shape on flow in discrete element method simulation of a rotary batch seed coater

Abstract

In the seed processing industry, rotary batch seed coaters are widely used for providing a protective coating layer (consisting of various ingredients including fertilisers and crop protection chemicals) on the seeds. Seed motion and mixing are important in ensuring uniform coating. In the batch seed coater, the base of a cylindrical vessel rotates, whilst the cylindrical wall is stationary and two baffles turn the bed over for mixing. In the present study, the Discrete Element Method (DEM) is used to simulate the effect of particle shape on motion and mixing in this device. Corn seed is used as a model material and the effect of its shape on motion is analysed by considering two approaches: (1) manipulation of rolling friction to account for shape as it is commonly used in the field; (2) approximation of the actual shape by a number of overlapping spheres of various sizes. The geometry of corn seeds is captured using X-Ray micro tomography and then the ASG2013 software (Cogency, South Africa) is used to generate and optimise the arrangement of the overlapping spheres. A comparison is made of the predicted tangential and radial velocity distributions of the particles from DEM and those measured experimentally. It is concluded that for rapid shearing systems with short collisional contacts a small number of clumped spheres suffices to provide a reasonable agreement with experimental results. Equally well, manipulating the rolling friction coefficient can provide results that match experiments but its most suitable value is unknown a priori, hence the approach is empirical rather than predictive. 2

Jamming during particle spreading in additive manufacturing

“…3. Each particle is approximated by a number of overlapping spheres of different sizes, following the multi-sphere approximation approach of Pasha et al [28]. …”

Repose angle of monoparticles and binary mixture: An experimental and simulation study

“…To select the range of the experimental design (central composite design) for the studied parameters, we have used a wider range found in the literature [3,8,9,17,21,[24][25][26][27][28][29][30][31][32][33][34] for DEM simulations of agricultural materials. However, it is still important to highlight that the calibration methodology used in this work allowed us, besides to identify appropriate values of these parameters, also to quantify their effects, as well as the interaction between them on the repose angle of these materials (as monoparticles and binary mixtures).…”

Distinct element analysis of inter-particle coating variability in a batch seed coater

“…The shape of corn seeds is then approximated with five clumped spheres (approximately 0.1 % deviation in volume compared to volume of the actual seed) with different sizes, as shown in Figure 2b. The validity of the approximation for predicting the motion of corn seeds in the coater has been previously demonstrated by Pasha et al [11]. A bed consisting of approximately 4200 seeds (21,000 spheres), corresponding to 1.4 kg of corn seeds, is used.…”