The influence of a seed drop tube of the inside-filling air-blowing precision seed-metering device on seeding quality

This work aimed to improve the seeding quality of maize and to investigate the influence of the seed drop tube on the seeding quality. The airflow-assisted seed-dropping device (the seed drop tube) was designed for an inside-filling air-blowing precision seed-metering device. The mechanism of the movement of the maize seeds in the seed drop tube was analyzed. The magnitude of the steady-state flow and the flow velocity of the steady-state airflow are analyzed for different combinations of structural parameters of the seed drop tube using computa-tional fluid dynamics. The flow field simulations yielded the maximum steady-state airflow velocity for a seed drop tube inlet diameter of 24 mm and a throat height of 30 mm. CFD-DEM coupled simulation was used to investigate the movement of maize seeds in a seed drop tube with a throat height of 30 mm and a seed drop tube inlet diameter of 24 mm. The collisions of the maize seeds and the time of their fall were analyzed. The analysis shows that the maize seeds collided after entering the seed inlet and before reaching the stable acceleration zone. The seeds fell quickly. The falling times of the seeds were nearly uniform. The mean and standard deviation values of the seed fall time were 0.12 +/- 0.008 s. High-speed camera and bench tests were used to verify the performance of the seed drop tube. Maize seed collisions captured by the high-speed camera were consistent with the coupled simulation tests. The influence of the seed drop tube on the qualified index and coefficient variation of the seed interval at different working pressures and different working speeds of the seed-metering device were compared and analyzed. The seed drop tube reduced the coefficient variation by 3.66 % at a working pressure of 4.5 kPa and a working speed of 41 r/min. At a working pressure of 4.5 kPa and an operating speed of 32 r/min, the seed drop tube increased the qualified index by 1.06 % and reduced the coefficient variation by 1.17 %. The lowest coefficient of variation at this point was 9.58 %, with a qualified index of 96.56 %.