(115a) Contact Algorithm for Tablet-Shaped Particles and Its Application in Dem Simulation

The characteristics of moving tablet-shaped particles are significantly different from those of spheres [1]. In order to capture the physics of tablet collisions, a more realistic model of the tablet shape is required. In recent work [2], the intersection of three convex spherical spheres has been used to represent the shape of a standard round tablet. Based on the geometry of tablet by using this representation, the contact algorithm for tablet - flat surface and tablet - tablet contact was developed and was implemented in Matlab^® code for the DEM simulation of tablet-tablet contact. A high-speed imaging system was also used to record the images of the tablet movement for one tablet hitting another stationary tablet stick to a flat surface. The angular velocity of the moving tablet was obtained by using the spreadsheet analysis module included in this image system to quantitatively analyze these images. The results showed good agreement for the angular velocity between experiments and simulations. In order to verify the accuracy and efficiency of this representation, multi-sphere representations for the shape of the tablet were also used in the DEM simulation of tablet - tablet contact by using 10, 26, 66, and 178 identical spheres, respectively. The computational times for a single tablet - tablet contact in 66- and 178-sphere representations were much higher than those for tablet simulations. In addition, comparison of these simulation results showed that the multi-sphere representation gives poor agreement for angular velocities. At the same time, DEM simulations considering the liquid effect on the dynamic behavior of two tablet contact showed that the existence of liquid in the particulate system is an important factor affecting the dynamic behavior of particulate system, especially for the tablet coating in a pan coater in pharmaceutical industry. The contact algorithm, along with appropriate normal and tangential force models, was implemented in a Matlab^® code for the multi - tablet simulation in order to investigate the dynamic behavior of tablets in a rotating drum. To account for the effect of shape on the dynamic behavior in a particulate system, spherical particles which have the same volume as the tablets was also simulated in the rotating drum. In this simulation, all physical properties of spherical particles were the same as the tablets and the initial conditions of both multi-tablet and multi-sphere simulation were identical. The simulation results showed that the surface velocities along the cascading surface for tablets were larger than those for spherical particles. In addition, the simulations showed that the angle of repose for tablets was larger than for spherical particles. Both of these two phenomena are consistent with the experiment work [1,3].

[1] P. Pandey, R. Turton, Movement of different shaped particles inside a pan coating device using novel video-imaging techniques, AAPS PharmSciTech 6(2), article # 34, 2005

[2] Y. Song, R. Turton, F. Kayihan, Contact detection algorithms for DEM simulations of tablet-shaped particles, Powder Technology (in press) 2005

[3] Pandey P., Song Y., Kahiyan F., Turton R., Simulation of particle movement in a pan coating device using a new MATLAB-based Discrete Element Modeling code, Powder Technology, in press