Investigating the Influence of Grain Drying with Ambient Air Versus Heated Air within an Eighth-Scale Grain Drying Bin

The choice of whether to use heated or ambient air during grain and oilseed drying is often complex, and it has a great effect on the overall quality of the product. A significant problem when drying with heated air is overdrying the bottom layer in attempting to dry the top layer. This is possible because grains or oilseeds within a storage bin can be more than 15.2 m deep. However, while the bottom layer is less likely to be overdried when using ambient air, there is a risk that the upper layers could be subject to mold and degradation if moisture is not removed quickly enough. An eighth-scale grain drying bin was equipped with temperature, moisture, and relative humidity sensors at different heights to observe temperature and moisture migration throughout the 60-cm deep bed as corn and wheat were dried. For both commodities, trials were run where they were dried with heated air and ambient air. Likewise, thin-layer drying models were applied to the deep bed, and the drying process was simulated using the finite difference method for both commodities using ambient and heated air. The absolute humidity, air temperature, grain temperature, and moisture content were modeled throughout the drying bed with respect to location and time. Data obtained from the simulations compared well with the experimental data. When comparing the moisture content determined from simulation with the same measured with the microwave moisture sensor within the drying system, root mean square error (RMSE) values for corn and wheat were 0.61 (heated air), and 0.45% and 0.50% (ambient air) moisture content wet basis (w.b.), respectively. A 30% increase in drying time was observed when ambient air was used to dry wheat. A 2-% increase in ending moisture content was observed when drying with ambient air for both commodities. The empirical results obtained from the eighth-scale drying system confirmed the results obtained from simulation for each trial. While results obtained may be unique to the current study, the effectiveness of the models was demonstrated.