Determining Effects of Fertilizer Particle Shape on Aerodynamic Properties

A method was investigated for determining the extent to which aerodynamic properties of fertilizer particles can be explained by a combination of turbulent airflow theory and a response surface involving geometric shape and mass of particles for a sample of specific fertilizer material. Fall tests were conducted, where particles were dropped and fall times were described by a mathematical model using turbulent airflow theory. Secondly, a measure of particle shape was determined to explain the difference between theoretical and measured fall times. Various dimensions of particles were measured using digital image processing. Absolute radius deviations from a preassumed best-fit circular shape were recorded and combined from two perpendicular particle images and designated “shape factor”. For a sample of calcium ammonium nitrate (CAN) particles, the shape factor ranged from 11.8 to 73.0 (perfect spheres are zero). Over that range, the difference between theoretical and measured fall times was satisfactorily explained (R2 = 0.82 ) by a function of shape factor and particle mass. A new approach to characterize a bulk of fertilizer material and its spreading properties was proposed.