Airflow Distribution and its Relation to Bulk Grain Drying
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Experimental and computer simulation of in-bin grain drying was conducted. The study was to model the non-uniform distribution of temperature and moisture content in bins with slanted or partially perforated floors, hence with non-parallel airflow streamlines. Complete data were obtained for grain drying with non-parallel airflow. These data included moisture contents, temperatures, static pressures, intergranular air velocities, and shrinkage of the drying beds. The intergranular air velocities measured were found to be about three times those calculated from the superficial air velocity divided by the bulk porosity. The non-parallel airflow regions were more pronounced near the air entrance. A way from the entrance regions, the air velocity profile tended to be uniform. The partially perforated floor created higher resistance to airflow than the totally or slanted perforated floors. The drying pattern depended on the floor configuration. For the slanted floor, grain at the center of the bin remained undried at about 20% moisture content when the average moisture content of the bin reached 14% (w.b.). Typical bulk shrinkage of grain was about 20% for grain dried from 22% to 12% moisture content. The shrinkage was non-uniform with the slanted floor. Grain shrinkage resulted in denser packing of the grain and an increase in the resistance to airflow. This increase was somewhat compensated for by a decrease in the grain bed depth. The net decrease in airflow supplied to the bin was about 13% . An improved simulation scheme was developed to simulate the airflow distribution and to compute heat and mass transfer processes along streamlines. The improved simulation scheme predicts the general pattern of moisture content. Under non-parallel airflow conditions, the model provides a better estimation of moisture content than it does of grain temperature. Accurate prediction of airflow distribution was needed to simulate the grain drying process accurately. More work is required to simulate three dimensional flow and drying with concurrent grain shrinkage.