Fertilizer injecting route analysis and test for air-blowing seed-fertilizer hole-applicator via CFD-DEM coupling

Abstract：The pneumatic hole-fertilization device can deliver a pre-calculated amount of fertilizer to pre-designed locations in soil and is hence effective in improving fertilizer use efficiency. The operation of the pneumatic hole-fertilization device consists of three steps: taking fertilizer, transporting it and injecting it to soil. To ensure accuracy in taking fertilizer, it needs to completely remove the fertilizer from the chamber in the device and curtail spatial distribution of the fertilizer in soil during the injecting process. The structure of the gas channel in the injecting component controls the quality of fertilizer transporting, while the fertilizer movement in the chamber remains elusive. There is a paucity of study about the impact of fertilizer-moving route on performance of the device. Depending on how the disposing outlet pipe is connected to the fertilizer-plate, the fertilizer injection can be divided into lateral injection and bottom injection. In this paper, we simulated the impact of the two injections on fertilizer movement using the discrete element method software - EDEM, and then coupled it with CFD to simulate gas flow and fertilizer movement under different inlet velocities. The results showed occurrence of backflow of the fertilizer as airflow velocity increased due to the disturbance caused to the fertilizer in the chamber when the connected area between the chamber and the inlet pipe was small. Increasing the connected area can attenuate gas flow velocity and reduce fertilizer disturbance, thereby stabilizing fertilizer movement. When the inlet velocity was 4 m/s, both injections worked poorly. Increasing the inlet velocity could improve fertilizer removal rate and the accumulation performance. When the inlet velocity was 8 m/s, the accumulation performance of fertilizer under lateral injection was superior to under bottom injection, while the bottom injection had the edge in fertilizer-clearing rate. We also conducted a bench experiment under different inlet velocities to compare the two injections by capturing the distribution and movement of fertilizer in the proximity of the outlet using a high-speed camera. The experimental results were consistent with the EDEM-CFD simulations. When the inlet velocity was 8 m/s, the fertilizer removal rate and the distribution length under the lateral injection were 85.5% and 9.9 cm respectively, while under the bottom injection they were 87.1% and 11.4 cm respectively. Comparing the EDEM-CFD simulation with the experimental results revealed that EDEM-CFD can be used as a tool to design and optimize the fertilizer route in the pneumatic hole-fertilization device.