Discrete-element method application to mixing and segregation model in industrial blending system
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In the pharmaceutical industries, mixing is a critical process. Pharmaceutical products consist of various components, including active ingredient and excipient. After mixing, we should get a homogeneous mixture to ensure the quality of the final products, such as tablets or capsules. For that reason, segregation is an unwanted phenomena in the mixing process. In this study, discrete-element method (DEM) was applied to investigate the mechanism of segregation in a rotating cylinder; basic equipment for powder mixing. In addition, segregation of particles in a rotating cylinder is a very interesting phenomenon and has captured the curiosity of not only industrial engineers, but also physicists. DEM can simulate segregation in a rotating cylinder three-dimensionally. In particular, radial segregation, which was quickly observed, was quantified by computing the granular temperature of the system. Furthermore, particle migration in axial direction, which may be the source of axial segregation, was also shown by the DEM simulation.
I. INTRODUCTION
Engineers have been interested in complicated granular flows, and many have studied them because mixing is an important process in industries where powders and grains are handled, especially in pharmaceutical manufacturing, where it is important to ensure the blend uniformity of mixtures. Segregation should be avoided in the blending process to maintain the quality of drug products, such as tablets and capsules. The phenomenon of segregation has captured the attention of physicists for a long time. The original study was performed in 1939 by Oyama,1 who first reported that rotating cylinders partially filled with a mixture of granular media may separate the individual species into bands along the rotational axis. This phenomenon is termed axial segregation. Since Oyama’s experiments, a number of studies have shown that mixtures of granular media exhibit a wide range of axial segregation (see, e.g., Refs. 2–7). It has been found from recent studies that the reversible axial segregation of different-sized granular media in a drum mixer is related to variations of the dynamic angle of repose,8 but it is also clear that subsurface effects are critical, because axial bands that do not extend to the surface have been observed within the bulk. To study the dynamics beneath the surface involved in the segregation process, discreteelement method (DEM) simulation was used in the current study to demonstrate granular flow patterns within a drum mixer as a function of granular temperature. By calculating the granular temperature, radial segregation was analyzed quantitatively. In this study, J. Mater. Res., Vol. 19, No. 2, Feb 2004
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granular temperature was first focused as a quantitative key-parameter to consider the source of radial segregation. This scale of DEM simulation for two different-size systems was conducted to calculate the granular temperature and was compared with previous experimental results. Furthermore, migration
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