Dynamic Porosity Characteristics of Corn Bed During Convective Drying: A Numerical and Experimental Study Based on EDEM–Fluent Coupled Simulation

During the grain drying process, porosity directly affects the pore curvature, effective evaporation area, and ventilation resistance of the granular bed, which is an important factor in determining the drying rate, energy consumption and drying uniformity. Existing research on the porosity of flowing maize beds is relatively limited and has primarily focused on static pile conditions. Therefore, this study designed an air convection measurement system consisting of a variable-frequency fan, a valve opening adjustment device, and a differential pressure sensor. The following factors were selected: moisture content (13.03–33.37% w.b.), air velocity (0.6–1.0 m/s), maize flow velocity (0.04–0.06 m/s), and bed thickness (20–40 cm). Experiments were conducted using a Box–Behnken design, and the measured results were compared with theoretical values from the Ergun equation and results from EDEM–Fluent coupled simulations. The dynamic porosity ranged from 57.81% to 63.30%. Porosity decreased as moisture content and pile thickness increased, while it increased as the corn flow velocity increased; air speed had a minor effect. The response surface model had an R2 value of 0.9600, and the relative deviations between the measured, simulated, and predicted values did not exceed ±1%. The conclusion is that water content, corn flow velocity, and pile thickness are the primary factors affecting dynamic porosity.