Technical Note: Field-observed angles of repose for stored grain in the United States

Authors: BHADRA, RUMELA - Kansas State University; Casada, Mark; TURNER, AARON - University Of Kentucky; BOAC, JOSEPHINE - Kansas State University; THOMPSON, SIDNEY - University Of Georgia; MAGHIRANG, RONALDO - Kansas State University; MONTROSS, MICHAEL - University Of Kentucky; MCNEILL, SAMUEL - University Of Kentucky

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2016
Publication Date: 1/15/2017
Publication URL: http://handle.nal.usda.gov/10113/5653780
Citation: Bhadra, R., Casada, M.E., Turner, A., Boac, J.M., Thompson, S.A., Maghirang, R.G., Montross, M.D., McNeill, S.G. 2017. Technical Note: Field-observed angles of repose for stored grain in the United States. Applied Engineering in Agriculture. 33(1):131-137. doi:10.1303/aea.11894.

Interpretive Summary: Grain, unlike liquid, forms a pile when unloaded on a solid surface. The pile is characterized by the angle it forms with the horizontal plane, known as angle of repose. The grain's angle of repose is a key parameter needed for stored grain inventory calculations and handling equipment design. Angle of repose is a function of inherent kernel characteristics, resulting in different angles for different crops, and the angle of the surface varies slightly when emptying a system compared to the angle that forms with a pile during filling. We measured piling angles of repose for corn, sorghum, barley, soybeans, oats, and hard red winter (HRW) wheat in steel and concrete bins and outdoor piles. The angle of repose for corn ranged from 15.7° to 30.2° (median of 20.4°). Sorghum, barley, soybeans, oats, and HRW wheat had median angles of 24.6°, 21.0°, 23.9°, 25.7°, and 22.2°, respectively. For these six crops the measured piling angles of repose were generally lower than typical values cited in a standard handbook from the Midwest Plan Service (MWPS-29), but higher than some laboratory measurements from other studies. The grain was measured at typical storage moisture contents during this study and, thus, did not have a wide enough moisture range to determine a correlation between angle of repose and moisture content. Accurate angle of repose information is important to elevator managers, farmers, and equipment designers because it is required information for grain inventory calculations and grain bin and grain handling equipment design. This study provides robust data on angle of repose in the field for these six crops.

Technical Abstract: Bulk grain angle of repose (AoR) is a key parameter for inventorying grain, predicting flow characteristics, and designing bins and grain handling systems. The AoR is defined for two cases, piling (dynamic) or emptying (static), and usually varies with grain type. The objective of this study was to measure piling angles of repose for corn, sorghum, barley, soybeans, oats, and hard red winter (HRW) wheat in steel and concrete bins in the U.S. Angles were measured in 182 bins and seven outdoor piles. The piling AoR for corn ranged from 15.7° to 30.2° (median of 20.4° and standard deviation of 3.8°). Sorghum, barley, soybeans, oats, and HRW wheat also exhibited a range of AoR with median values of 24.6°, 21.0°, 23.9°, 25.7°, and 22.2°, respectively. Angles of repose measured for the seven outdoor piles were within the ranges measured for the grain bins. No significant statistical correlation was observed between AoR and moisture content, unlike previous literature based on laboratory measurement of grain samples with wider ranges of moisture content than those observed in this study. Overall, the measured piling AoR were lower than typical values cited in MWPS-29, but higher than some laboratory measurements.