Darcy’s law is a function of viscosity, permeability, and velocity and can be used to predict the airflow resistance in granular materials at low air velocities. Permeability also governs the magnitude of natural convection currents during periods of non-aerated grain storage. The permeability of corn, soybeans, soft white winter wheat, and soft red winter wheat were measured as a function of bulk density and moisture content. Air was passed through a column of grain and the flow rate and pressure drop measured. Bulk density and kernel density were also measured to determine the porosity of grain in the test column. Two filling methods were used to change the bulk density of grain by approximately 50 kg/m3, an increase of 7%. This resulted in a reduction in porosity of approximately 4 percentage points. However, permeability decreased by a maximum of 45%. Wheat had the lowest permeability (between 1.15 × 10-8 and 7.29 × 10-9 m2 or highest resistance coefficient between 1591 and 2510 Pa.s/m2, respectively, depending on bulk density and moisture content), while corn and soybeans were similar (permeability varied between 1.30 × 10-8 and 3.03 × 10-8 m2 or resistance coefficient between 1,408 and 604 Pa·s/m2, respectively). Experiments were conducted up to an air velocity of 0.0052 m/s that resulted in a Reynolds number of 2.5, which was slightly above the maximum air velocity expected during non-aerated grain storage. Nevertheless, Darcy’s law would be appropriate for predicting natural convection currents during non-aerated storage.
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The authors wish to acknowledge the financial support of USDA-NRI under contract number 2001-35503-10025.
This article is published with the approval of the Director of the Kentucky Agricultural Experiment Station and designated paper number 03-05-115.
Montross, Michael D. and McNeill, Samuel G., "Permeability of Corn, Soybeans, and Soft Red and White Winter Wheat as Affected by Bulk Density" (2005). Biosystems and Agricultural Engineering Faculty Publications. 81.