Discharge Validation of Cylindrical Feed Pellets in Conical Hoppers Using Discrete Element Method

Prolonged storage of pelleted feed causes arching above the outlet of conical silos, yet how far the wall material governs the discharge stability of non-spherical pellets remains unresolved. An experimentally calibrated Discrete Element Method (DEM) framework was established in Ansys Rocky for the gravity discharge of cylindrical feed pellets (2 mm × 5 mm, aspect ratio 2.5) from 1:10 scaled steel and fiberglass conical silos at an outlet-to-particle-size ratio of approximately 18, after 4 h of consolidation. Of the hopper half-angles tested (10°, 20°, 30° and 45°), only 10° sustained gravity discharge; the others blocked completely in both wall materials. Parameters calibrated from consolidated-load direct shear tests reproduced the cumulative discharged mass to a MAPE of 2.5% (R2 = 0.99, steel) and 3.9% (R2 = 0.963, fiberglass), whereas the instantaneous flow rate remained stochastic. Both silos discharged in pulses, at 0.94 and 0.79 kg/s, with coefficients of variation of 25% and 28%. Mass flow indices of 0.211 and 0.278 place both in the funnel-flow regime, and measured peak wall pressures near the outlet reached ≈2000 Pa (steel) against ≈1650 Pa (fiberglass). Reducing wall friction from 0.83 to 0.74, therefore, did not improve stability: for elongated pellets at a low outlet-to-particle-size ratio, surface smoothness alone is no remedy, and outlet sizing, interlocking and wall load management must be addressed together.