An improved coarse-grained DEM model for wet particle behavior in a pan pelletizer

In discrete element method (DEM) analyses of wet particle behavior in a pan pelletizer, coarse-grained models are often employed to reduce computational costs. However, conventional coarse-graining methods often suffer from significant errors, including an imbalance between particles constrained by walls and freely moving particles, and an overestimation of their velocity. In this study, we developed a modified coarse-grained model to address these discrepancies. Our model conceptualizes coarse-grained particles by partitioning them into two distinct zones: an external zone for direct contact with other particles and walls and an internal zone representing the contribution of primary particles contained inside the coarse-grained particle. Additionally, to address the underestimated damping effect caused by the decrease in the coordination number at higher coarse-graining ratios, we introduced a compensation method for particle damping. Simulations conducted at coarse-graining ratios of 2 and 3 using 1 mm particles, and 2, 4, and 6 using 0.5 mm particles, demonstrated that the proposed method improved agreement with the original particle system and experimental results compared to conventional models. Under the 30 and 40 rpm conditions, the proposed model reproduced the collapse shape, bed-lift height, and particle–wall relative velocity distribution observed in experiment.