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United States Department of Agriculture

Agricultural Research Service


Location: Engineering and Wind Erosion Research Unit

2013 Annual Report

1a.Objectives (from AD-416):
Obtain new field and laboratory data to refine and calibrate a science-based model for determining the packing of grains within upright storage structures. Laboratory data on bulk grain compression characteristics will be obtained for wheat, corn, soybeans, grain sorghum, oats, and barley. The effect of bin vibration on packing factor will also be investigated laboratory bins designed for that purpose. Field measurements of grain packing will be obtained from several states in the eastern U.S. in partnership with collaborators at ARS, Kansas State University, and the University of Georgia who will also make field measurements. Field data will be collected primarily for wheat, corn, and soybeans and also for grain sorghum, oats, and barley when those crops are available.

1b.Approach (from AD-416):
This research is part of a larger, nationwide project to refine and validate a procedure with known accuracy, based on measurable physical parameters, for determining the packing of grains within upright storage structures. Because grain is somewhat compressible when subjected to the cumulative weight exerted from the material above, accurate packing factors are required to determine the mass of grain in storage from bin dimensions and test weights. Inventory control is critical for stored grain managers due to financial aspects (auditing by state agencies) and for the future utilization of quality management systems. The major variables affecting stored grain packing are grain type, moisture content, test weight, internal friction, and bin wall material, geometry, and dimensions. Variation across different regions of the U.S. must be investigated as well as other minor factors. A preliminary model for determining packing factors for a wide range of grains and bins is being developed that employs the differential form of Janssen’s equation to estimate the pressure and in-bin bulk density for a given depth of grain in a bin. In the larger project, this model will be calibrated and validated by measuring packing factors for selected grains in bins in all of the major grain producing regions of the U.S. As part of that nationwide effort, the Cooperator will measure packing factors in selected states in reasonable proximity to their locations. Improved estimates of the compressibility of grains as a function of overburden pressure will be obtained using a laboratory apparatus designed to simulate internal pressure from various depths of overbearing grain. Field measurements of packing factors will be obtained by measuring the height of grain in bins of known dimensions and wall materials as they are filled and/or discharged with a measured mass of grain.

3.Progress Report:

Laboratory tests were designed to evaluate the effect of dockage levels on compressibility of hard red winter (HRW) wheat samples under applied pressure. Dockage levels of 0%, 1%, and 5% were tested with these samples. Results indicated that increasing dockage increased both the compressibility and variability in the data. Test weight decreased with dockage, as expected, while lower test weights produced greater compressibility, which led to compressibility increasing with increasing dockage. This test weight effect was consistent with previous results, which showed that with soft red winter (SRW) wheat samples higher initial sample density (higher test weight) yielded lower grain compressibility and, thus, lower packing. With lower initial bulk density the interstitial air space increased, which resulted in the bulk grain being more compressible. Thus, the overall effect of higher dockage was to lower test weight, which in turn increased the compressibility. A wide range of corn samples have also been tested for compressibility as a function of pressure in the laboratory compressibility box and data are being processed. Compressibility modeling studies were conducted to determine the most appropriate models for fitting the constant-moisture pressure data from the laboratory compressibility box. In addition to the standard data normally collected from the compressibility box up to about 20 psi, data were also obtained from a modified box up to 130 psi and from a small compressibility cylinder up to about 3600 psi. The density appeared to approach an asymptote in the compressibility box at the 20 psi upper limit used in standard tests. Data at higher pressures showed this was not a true asymptote and there was an inflection point where densities began to increase at a higher rate again at higher pressures. (The inflection point was about 500 psi in the compressibility sensor, but the magnitude of pressures in that cylinder is not directly comparable to that in the standard compressibility box.) The asymptotic models showed apparent asymptotes in the standard tests as high as 70 lb/bu, while density in the small compressibility cylinder reached as high as 90 lb/bu and the theoretical density limit is 110 lb/bu based on the kernel densities. Models were selected to cover the range of pressures in grain storage bins, up to 20 psi, and model predictions would be inaccurate above those levels. Overall the modified Page and Farazdaghi-Harris models were better than the others for characterizing this density data up to pressures of 20 psi. This extensive laboratory data is contributing to a greater understanding stored grain packing factors and should provide greater confidence in the packing factor predictions being developed compared to the old packing factor predictions.

Last Modified: 7/25/2014
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