Variability of pressure drops in grain generated by kernel shape and bedding method

Experiments were performed to evaluate the influence of seed shape and the packing orientation of seeds on the pressure drop. Relationships between the pressure drop and airflow velocity of five seeds were determined as a function of filling method and its influence on kernel orientation. The sample container was a cube with a length of 0.35 m on each side that held approximately 35 kg of clean wheat. Eleven airflow rates were supplied in a range from 0.03 to 0.35 m s−1. Seeds that were nearly spherical (rapeseed and pea) as well as oblong seeds (wheat, rye and oats) were used for the tests. Three filling methods of the cube were used, including one that produced asymmetric particle orientation (bedding) within the grain sample. Pressure drop was measured in all three directions: the vertical (Z) and both horizontal directions (X and Y). Results obtained from the experiments showed that seed shape and the filling method strongly influenced pressure drop. At an air velocity of 0.3 m s−1, when the cube was filled along the vertical axis the uncompacted samples had a pressure drop in the vertical direction that was 1.1 (peas) to 2.1 (oats) times higher than the pressure drops along the X and Y axes. The pressure drops along the X and Y axes were approximately equal. Compaction of the sample filled vertically resulted in the pressure drop in the vertical direction increasing between 1.7 (wheat, rye and peas) and 2.4 (oats) times the pressure drop in the uncompacted sample. In asymmetrically filled samples the pressure drops along the horizontal directions increased by a factor of 2.2 relative to the centrally filled samples.