Moisture-Dependent Granular Flow, Stratification, and Stone–Grain Segregation Dynamics in Vibratory Gravity Rice De-Stoning Systems

Abstract

Moisture-dependent granular segregation remains a critical limitation in vibratory gravity rice de-stoning systems, where stones and grains exhibit overlapping size distributions but differ in density, morphology, and surface properties. Although granular segregation under gravity and vibration has been widely studied, most existing investigations focus on dry or idealized particle systems, providing limited insight into realistic agricultural materials where moisture-induced cohesion plays a dominant role. Unlike previous studies focused on dry or idealized particles, this work provides experimentally validated evidence of nonlinear moisture–vibration–gravity coupling in realistic agricultural granular systems. This study experimentally investigates the coupled effects of moisture content, vibration kinematics, and gravity on granular flow, stratification, and stone–grain segregation in a vibratory gravity rice de-stoner using FARO-44 and NERICA-11 rice varieties. Experiments were conducted at moisture contents of 10–14% (wet basis), shaker angles of 12–15°, and varying pulley diameters using a factorial experimental design combined with analysis of variance and response surface methodology. Results show that stone recovery efficiency decreases monotonically with increasing moisture content due to capillary-induced cohesion, which suppresses kinetic sieving and density-driven percolation. Shaker angle emerged as the dominant mechanical control parameter, with 15° providing optimal stratification through a balance of gravitational transport and vibration-induced lift, while pulley diameter contributed primarily through interaction effects by stabilizing vibratory energy transmission. Quadratic response surface models exhibited strong predictive capability (R² > 0.90), confirming the nonlinear nature of moisture–vibration–gravity interactions. Multi-objective optimization identified an optimal operating condition of 144 mm pulley diameter, 15° shaker angle, and 10% moisture content for FARO-44 rice, achieving approximately 84% cleaning efficiency, 57 kg h⁻¹ throughput, and 690 kg per 12 h capacity with a desirability index of 0.991. The findings provide a physics-based interpretation of moisture-controlled granular segregation and offer a statistically validated operational framework for improving separation efficiency in vibratory gravity de-stoning systems.