Heat and moisture transfer during aeration of maize grain piles with heterogeneous porosity formed by central loading

Porosity heterogeneity formed during silo loading is often omitted from continuum models despite its influence on airflow and coupled heat and moisture transfer. This study examined its effects in a 1.5 m diameter, 3.0 m high small-scale silo using loading tests, stratified sampling, a 96 h aeration experiment, and computational fluid dynamics simulations. Radial distributions of broken kernels, impurities, other grains, and porosity were measured at several drop heights. These measurements and a vertical pressure correction were used to construct the porosity field. Temperature predictions were evaluated against measurements and compared with a constant porosity model. Broken kernels and fine materials accumulated mainly in the central region, whereas coarse impurities occurred near both the center and wall. Corrected porosity ranged from 0.411 at the bottom center to 0.462 near the upper wall. With heterogeneous porosity, airflow shifted toward the wall, where velocity was about 40% higher than at the center, and the bottom pressure drop was 12.69% higher than in the constant porosity case. The constant porosity model over-predicted early cooling by up to 4.27 °C, whereas the heterogeneous model reproduced slower cooling at the center and faster cooling near the wall. Because spatially resolved grain moisture measurements were unavailable, moisture fields were interpreted qualitatively and suggested slower moisture reduction in the upper central region. Including the measured porosity distribution improved airflow and temperature predictions and provided a theoretical indication of spatial moisture migration. Fitted front relationships apply only to the tested silo geometry, airflow rate, and boundary conditions.