Percolation segregation of multi-size and multi-component particulate materials

Percolation segregation of fines in multi-size and multi-component mixtures was quantified and compared with continuous mixtures. The quantification and comparison of percolated fines in binary, ternary, and quaternary vs. continuous mixtures was done at two strain rates of 0.25 and 0.5 Hz for both urea (spherical-shaped) and potash (angular-shaped). For this study, three coarse and three fines sizes for potash and three coarse and two fines sizes for urea were used for preparation of multisize and multi-component mixtures. Binary mixture samples were prepared from three mean coarse sizes with their corresponding three and two fines sizes for potash and urea, respectively. Ternary mixture samples were prepared from two coarse sizes at a time from the three available coarse size particles with their corresponding fines one each from three and two fines sizes available for potash and urea, respectively. Quaternary mixture samples were prepared from three coarse sizes with their corresponding two fine sizes (1850 μm, and 1550 μm) for potash and urea, respectively. The percent segregated fines mass and the normalized segregation rate (NSR) of fines decreased with the increase in number of coarse size components for a given fines size (from binary to quaternary), where NSR is defined as the amount of fines percolated from initial fines present in the binary mixture based on total time of operation kg/kg-h. The NSR decreased with the increase in order of mixtures, i.e., binary > ternary > quaternary at two strain rates of 0.25 Hz and 0.5 Hz (p < 0.05). Based on results, it was found that the segregation in continuous mixtures can be predicted by studying the multi-size mixtures.     

Discrete element method study on hopper discharge behaviors of binary mixtures of nonspherical particles

This study is aimed at unveiling the influence of binary mixtures of nonspherical particles on hopper discharge behavior, which remains poorly understood. The discrete element method (DEM) is employed to simulate seven particle types with aspect ratios between 0 and 2 (namely, a sphere, two ellipsoids, two cylinders, and two cuboids) with the same volume. Seven monodisperse systems and twelve binary-shape mixtures are assessed. For the monodisperse systems, particle shape is the dominant factor dictating discharge rate, compared to other factors like aspect ratio, preferential orientation, and packing. Regarding the binary-shape mixtures, the discharge rates are similar for all twelve mixtures, reflecting a surprising lack of shape effects, which in turn means the negligible impact of solid volume fraction, aspect ratio, and segregation extent. Moreover, collision force is generally negatively correlated with discharge rate.     

Preparation of graded materials for miscible polycarbonate/poly(methyl methacrylate) blends by segregation under shear flow

Exposure to shear flow produced by a pressure-driven capillary rheometer provides a concentration gradient without phase separation in miscible polymer blends of bisphenol-A polycarbonate containing low-molecular-weight poly(methyl methacrylate) (PMMA). The strand surface extruded from the rheometer contains a large amount of PMMA. However, the strand is transparent because there is no light scattering due to phase separation. The segregation behavior, that is, enrichment of the PMMA content at the strand surface, is enhanced when the molecular weight of PMMA is low. Furthermore, the segregation is also enhanced at high temperatures and at high shear rates. By contrast, the die length barely affects the degree of segregation. The segregation phenomenon should be noted because it may facilitate the modification of the surface properties of various products.