Analysis of paddy grain hulling behaviour for rice grain quality improvement in centrifugal hulling using CFD-DEM method

As a vital staple food, paddy grain must undergo a hulling process before being converted into edible rice. In centrifugal hulling, the unstable motion of paddy grains inside the huller can lead to compromised rice grain quality. A limited mechanistic understanding of grain motion and orientation restricts effective control over hulling performance and quality. Therefore, this study employs a coupled CFD-DEM approach to systematically analyse the relationship between grain orientation and impact velocity during centrifugal hulling. The results demonstrate a clear correlation between the impact velocity and the orientation angle of paddy grains. Specifically, horizontally aligned grains predominantly undergo rolling motion and exhibit higher velocities, whereas vertically aligned grains tend to slide and exhibit lower velocities. Boundary effects cause adjacent grains to adopt a vertical alignment, while grains in the central region align horizontally due to frictional interactions with the impeller blades. Based on these findings, this study proposes a convex-curvature blade that reduces velocity differences by controlling the orientation angle of paddy grains. The optimised blade improves the hulling performance for paddy grains with different aspect ratios. These findings provide insights that could contribute to the enhancement of global food security. • CFD-DEM is used to analyse paddy grain motion in the hulling chamber. • Boundary effects and blade friction collectively influence grain orientation. • Disordered orientation stems from competition between sidewalls and blades. • Better vertical alignment lowers grain velocity differences. • Findings help enhance post-hulling rice quality while reducing losses.