Study on heat and moisture transfer of nonspherical rice during hot‐air drying in thin‐layer grain pile

Abstract

AbstractTo investigate fluid flow and coupled heat‐moisture transfer in the hot‐air drying of grain piles, this study integrated the discrete‐element method with computational fluid dynamics. A model for a thin‐layer grain pile, consisting of nonspherical rice particles represented by 13 spheres, was developed. Using a heat‐moisture transfer model based on fluid–solid coupling, the drying process with hot air was simulated and validated against experimental data. Finally, by controlling the drying temperature and the initial moisture content of rice, the variations in temperature and moisture content during the hot‐air drying process were explored. The numerical results indicated that the nonuniform pore structure within the grain pile, gaps on the surface of nonspherical rice, and the wall effect led to complex airflow patterns, resulting in the formation of dead zones within the grain pile. The oscillation frequency and amplitude of radial porosity near the wall were relatively large, and the minimum porosity occurred at a radial distance of 1/2dg. Heat and moisture transfer rates between the rice and drying air were influenced by the temperature and moisture concentration differences. During the drying process, variations in temperature and moisture content were observed among rice particles. Limited by the moisture diffusion coefficient, there existed a notable disparity in moisture content between the interior and surface of the rice. The results also showed that the curvature of the drying curve in the grain pile varied and was influenced by the drying conditions, especially under the high‐temperature drying condition of 60°C.Practical ApplicationsIn this study, a grain pile model for nonspherical rice particles composed of 13 spheres was developed based on the discrete‐element method and computational fluid dynamics. Furthermore, in accordance with the heat and mass transfer mechanism of fluid–solid coupling, a heat‐moisture transfer model for the hot‐air drying of the grain pile was constructed. This was done to deeply explore the internal fluid dynamic characteristics and the heat‐moisture transfer within the grain pile during the drying process. The newly established model can be widely applied to numerical simulation studies of drying and also has reference value for the design of drying systems.