DEM investigation of particle flow in a vertical rice mill: Influence of particle shape and rotation speed

The obscure milling mechanism, causing by diversity of rice grain shape, restricts appropriate selection of processing conditions for improving milling quality of different varieties. On this basis, the rice grain was represented as an axi-symmetric ellipsoid using discrete element method (DEM). Effects of particle shape and roller shaft rotation speed as well as the interplay of both on axial dispersion, radial exchange, spatial orientation and collision characteristics relating to the milling mechanism were analyzed. The results indicated that effects of aspect ratio on the milling uniformity depend on rotation speed, displaying the axial dispersion coefficient and mean effective collision rate increase with increasing aspect ratio in the lower rotation speed, whereas completely opposite in the higher rotation speed. Effects of aspect ratio on the milling intensity are independent of the rotation speed, showing radial ectopia number, variance of orientation distribution and mean collision energy all increase with increasing aspect ratio. • Milling of non-spherical particle with different shapes is simulated using DEM. • Effects of interaction of aspect ratio and shaft speed on flow behaviors are studied. • Longer rice grain undergoes intense milling compared to shorter rice grain. • Rice grain with larger aspect ratio has uniformity of milling in lower shaft speed.