Influence of Head Geometry on the Distributive Performance of Air-assisted Seed Drills

Abstract

Systematic design of distributor heads for air-assisted drills has not been fully developed because of its inherent complexities. Apart from the aerodynamics of the distributor, the mechanics of seed flow in air is governed by quite a number of factors, such as the properties of the seeds, the quantity of seeds in the distributor at any instant of time, input air velocity and many other such parameters. In the absence of theoretical procedures for designing the distributor head, three heads with different aerodynamic configurations, namely parallel disc, closed funnel and streamlined flow were made and evaluated on a test rig exclusively developed for varying the seed feed rate and input air velocity. The distributive performance was studied for three types of seed namely sesame, pearl millet and sorghum. While distributing sesame, the velocity at the distributor outlet for a given input air velocity and seed rate, was 6–8% lower with the closed-funnel distributor than with the other types. Here, the lower air velocity was a manifestation of the clogging and turbulence as caused by its aerodynamic configuration. The clogging caused a lack of uniformity in the distributed air velocities between the outlet tubes, which ultimately lowered the uniformity of seed distribution. The ability of the distributor to output equal quantity of seeds to individual outlet tubes, termed as uniformity of distribution was correspondingly poor (33–40%) at input air velocities less than 4·5 m/s and seed feed rate less than 68 g/min with the closed-funnel distributor. Similarly, in the case of pearl millet and sorghum also, the closed-funnel distributor offered lower uniformity of seed distribution. The uniformity greatly depended on the seed feed rate rather than the input air velocities for pearl millet. On analysing the performances of the distributors, the head offering a streamlined flow was found to yield the best distributive performance for all the three types of seed. It offered 98·6% uniformity at 5·5 m/s input air velocity and 79 g/min seed feed rate for sesame. The uniformity obtained for pearl millet was 98·5% at 6·0 m/s input air velocity and 168 g/min seed feed rate and was 99·4% for sorghum at 8·0 m/s and 238 g/min. Hence, while developing a distributor for an air-assisted drill, procedures such as the finite element method can be adopted to iteratively model the head's shape towards streamlining the flow and thereby to improve the distribution efficiency.