How bellows design solves the problem of uneven seed distribution in pneumatic seeding systems？
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Credit: HIGHER EDUCATON PRESS
In the field of modern agricultural machinery, pneumatic conveying seed-discharge systems have been widely adopted due to their compact size, high seed-discharge efficiency, and strong adaptability, which are particularly aligned with the current development trend of high-speed mechanized operations. Such systems mainly consist of seed dischargers, distributors, seed-mixing devices, and delivery pipelines. They transport and distribute seeds to different seeding rows through high-speed airflow, enabling efficient sowing. However, existing research has mostly focused on optimizing core components such as distributors and Venturi tubes, with insufficient attention paid to the critical link of delivery pipelines. After passing through 90° bends, seeds tend to form particle bundles on the outer side of the pipeline due to inertial forces, leading to uneven subsequent distribution and affecting sowing quality. How to solve this problem by optimizing the pipeline structure, especially the design parameters of bellows, has become the key to improving the performance of pneumatic seed-discharge systems.
Professor Ruiyin He from the College of Engineering, Nanjing Agricultural University, and his team proposed a bellows structure optimization scheme based on the EDEM-Fluent coupled method, systematically analyzing the influence of bellows parameters on the uniformity of rice particle distribution in the flow field. The relevant research has been published in Frontiers of Agricultural Science and Engineering (DOI: 10.15302/J-FASE-2025651).
The research team first determined the overall pipeline layout through numerical simulations: the horizontal pipe adopts a 300-mm straight pipe section connected to vertical bellows as a transition to avoid particle accumulation at bends. Subsequently, the L9(34) orthogonal test method was used to optimize four parameters—corrugated circle radius, bellows length, corrugation spacing, and corrugation length—with the coefficient of variation of the uniformity of bellows outlets as the evaluation index. The results showed that when the corrugated circle radius is 8 mm, bellows length is 500 mm, corrugation spacing is 40 mm, and corrugation length is 16 mm, the coefficient of variation of particle distribution in the pipeline reaches 3.46%, with significantly improved uniformity.
To verify the applicability of the optimized scheme, the team conducted bench tests under different flow rate conditions indoors. Under three particle mass flow rates (33.5, 67.0, and 101 g·s–1), when the bellows length is in the range of 400−500 mm, the coefficient of variation of the row discharge volume of the system meets the requirements of national standards. Among them, the 500-mm-long bellows performed optimally under all flow rates, with coefficients of variation of 3.26% ± 0.46%, 2.11% ± 0.54%, and 2.37% ± 0.27%, respectively.
The research innovatively proposed three basic principles for the piping design of pneumatic seed-discharge systems: the horizontal pipe is designed as a straight pipe to shorten the airflow stabilization stroke of the vertical pipe; the initial section of the vertical pipe is set as a straight pipe to avoid particle clogging; and the optimal bellows length is 400–500 mm to meet the installation needs of different machine models. Through EDEM-Fluent coupled simulations, the study also revealed the dual mechanism of “collision dissipation-vortex perturbation” for particle motion in bellows: the corrugated structure changes the particle trajectory, increases collisions between particles and between particles and the pipe wall, and uses vortex perturbation to promote particle dispersion, thereby achieving uniform distribution within a shorter pipeline length. The research results provide a reference for the optimization of pneumatic seed-discharge systems and have practical value for promoting the development of precision seeding technology.