Abstract
Discrete Element Method (DEM) simulations have the potential to provide particle-scale understanding of twin-screw granulators. This is difficult to obtain experimentally because of the closed, tightly confined geometry. An essential prerequisite for successful DEM modelling of a twin-screw granulator is making the simulations tractable, i.e., reducing the significant computational cost while retaining the key physics. Four methods are evaluated in this paper to achieve this goal: (i) develop reduced-scale periodic simulations to reduce the number of particles; (ii) further reduce this number by scaling particle sizes appropriately; (iii) adopt an adhesive, elasto-plastic contact model to capture the effect of the liquid binder rather than fluid coupling; (iv) identify the subset of model parameters that are influential for calibration. All DEM simulations considered a GEA ConsiGma™ 1 twin-screw granulator with a 60° rearward configuration for kneading elements. Periodic simulations yielded similar results to a full-scale simulation at significantly reduced computational cost. If the level of cohesion in the contact model is calibrated using laboratory testing, valid results can be obtained without fluid coupling. Friction between granules and the internal surfaces of the granulator is a very influential parameter because the response of this system is dominated by interactions with the geometry.
Highlights
The results from both model types are in excellent agreement, verifying that the periodic system is capable of reproducing the same phenomena observed in the full-size simulation and can safely be used in the sensitivity study to investigate the effect of the various Discrete Element Method (DEM) parameters
Discrete Element Method (DEM) simulations were used in this study of the particle dynamics that occur in a twin-screw granulator comprising both conveying and kneading elements
The DEM simulations for a cohesionless system provide a mean residence time—a key characteristic of a twin-screw granulator (TSG)—that is in line with expectations when compared to experimental results with various different granulators and cohesive materials
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Several experimental studies have investigated the effects of key process variables [26,27,28,29,30,31,32,33,34,35,36,37], screw configurations [24,25,38,39,40,41,42] and formulation variables [26,36,40], and have resulted in a regime map [43] of the twin-screw granulator. Zheng et al [60] have used DEM to study residence time distributions for dry, cohesionless, mono-sized elastic spheres of various sizes for a fixed configuration of conveying elements with two blocks of kneading elements at various operating RPMs. Zheng et al [61] extended the study further to include the effect of particle shape in the TSG. Validation of the model outputs against careful experimental measurements such as granule porosities and granule size distributions is not part of this study
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