The uniform removal of the bran layer significantly enhances the nutritional and economic benefits of rice. However, the influence of parameter conditions on the uniformity of milling in the abrasive milling process remains unclear. This is not conducive to improving the quality of rice milling. In this study, the effects of rotational speed and filling volume on milling uniformity in abrasive milling were investigated by combining experimental methods and simulation. The results showed that the higher the rotational speed, the more uniform the milling. The higher the filling volume, the more non-uniform the milling. The main reason for the variation in milling uniformity is the axial and radial position exchange of the rice particles in the milling chamber. The more frequent the exchange, the higher the milling uniformity. Subsequently, the frequency of position exchange was quantitatively characterised using axial and radial exchange rates, respectively. The rotational speed and filling volume change the position exchange frequency by affecting the rotational kinetic energy of the rice particles and the degree of dense rice population, respectively. These findings are useful in promoting rice loss reduction and nutritional balance.

Agricultural materials frequently undergo fragmentation due to high-stress conditions during processing, storage, and transportation. Throughout these processes, the spatial arrangement and morphology of particles continuously evolve, rendering the breakage behaviour of particle groups particularly complex. Thus, an in-depth understanding of the fracture processes and breakage mechanisms within particle beds holds significant research value. This study systematically investigates the breakage behaviour of rice particle groups under confined compression through an integrated methodology combining experimental testing, X-ray CT imaging, and finite element modelling (FEM) based on the cohesive zone model (CZM). Results demonstrate that, at the granular assembly scale, external loads are transmitted through force chains and progressively attenuate. As compression proceeds, stress disseminates toward peripheral particle regions. At the individual particle level, particle breakage results from the intricate interaction between coordination number (CN) and localized contact stress, with tensile stress playing a predominant role in the fracture process. An increase in coordination number promotes a more uniform stress distribution and inhibits breakage, thereby exhibiting a “protective effect”. These findings provide valuable insights for the design and optimization of grain processing equipment, contributing to a deeper comprehension of particle breakage characteristics.

The impact velocity of the grains is a critical factor affecting the hulling efficiency in centrifugal hullers. However, significant differences in velocity are observed among paddy grains following acceleration by the impeller. Therefore, elucidating the mechanism responsible for these velocity differences is essential for improving hulling performance. This study employed coupled CFD-DEM simulations to analyse the kinematic behaviour of paddy grains. The results demonstrate that velocity differences among grains are prevalent within centrifugal hullers and adversely affect hulling efficiency. These differences primarily arise from tangential collisions between grains and blades prior to acceleration, as well as axial collisions during the acceleration phase. The jumping degree (S_v) quantifies the relative motion between paddy grains and blades in the normal direction. Velocity differences decrease significantly as the jumping degree approaches unity. Furthermore, a tilted curvature blade was developed to mitigate velocity differences. Computational analysis and simulation determined that a blade curvature of 300 mm combined with a 20° tilt angle achieved the most substantial reduction in velocity differences. This optimised configuration improves hulling efficiency by 4.5% compared to the original blade design. This modification is expected to substantially facilitate the optimisation of centrifugal huller designs.