Aerodynamic Properties of Jatropha Seeds

Accurate scientific data are crucial to efficient design of machines for cleaning, separation, drying and postharvest handling of agricultural materials such as Jatropha seeds. Therefore this study was undertaken to determine the terminal velocity and drag coefficient of native and improved accessions of Jatropha seeds at four moisture content levels (4%, 8%, 12% and 16% db). The aerodynamic properties were determined using theoretical and experimental methods. The experimental method involves the use of a vertical wind tunnel. The values of terminal velocity obtained from the theoretical methods ranged from 5.72 – 13.24m/s for native accession and 6.45 – 13.45m/s for improved accession. On the other hand, values of terminal velocity obtained from the experimental method ranged from 7.98 – 11.08 m/s for native accession and 7.42 – 11.36 m/s for the improved accession. The drag coefficient values obtained from the theoretical methods ranged from 0.27 – 1.67 and 0.292 – 1.474 for the native and improved accessions, respectively. The experimental values of drag coefficient ranged from 0.07 – 0.173 for the native accession and 0.07 – 0.164 for the improved accession. Moisture content was observed to have a significant effect (p < 0.05) on both terminal velocity and drag coefficient. Conversely, the accession had no effect on any of the aerodynamic properties. Means separation using Duncan's Multiple Range Test showed that the difference, for the experimental terminal velocity, lies between 8 to 12% for native accession and 8 to 16% for improved accession. These moisture contents are the points at which the seeds gain significant weight to alter its terminal velocity. Regression equations for determination of terminal velocity and drag coefficient of Jatropha seeds were obtained for different moisture content levels using the mass of the seeds.