Research on the hydraulic conveying characteristics of floating feed pellets in horizontal pipes based on the CFD-DEM coupling method

Hydraulic conveying of aquaculture feed pellets through pipes has recently been adopted in offshore fish farms, but design guidelines for safe and energy-efficient operation are still lacking. In this study. In this study, the hydraulic conveying characteristics of floating aquaculture feed pellets within horizontal pipelines were investigated based on the CFD-DEM coupling method. In this study, a two-way coupled CFD-DEM framework is used to investigate the hydraulic conveying characteristics of floating feed pellets in a horizontal pipe with an inner diameter of 0.10 m and a total length of 3.0 m. Water with an inlet velocity of 2.0 m·s−1 and a pellet mass flow rate of 0.3 kg·s−1 is considered. The feed pellets are modeled as cylinders with diameter-to-length ratio ϕ in the range 0.4–1.6 and pellet size ratio ζ in the range 0.06–0.12. After validating the CFD-DEM model against classic experimental data for coarse spherical particles, the effects of ϕ and ζ on conveying velocity, cross-sectional distribution, collision frequency, energy loss and fluid pressure drop are systematically analyzed under statistically steady conditions. The results show that pellet shape strongly affects conveying behavior: increasing ϕ reduces pellet-wall collision frequency and associated energy loss, whereas increasing ζ enhances energy loss and significantly increases pressure drop. In all cases, pellet-pellet collisions are more frequent than pellet-wall collisions, but pellet-wall impacts dominate the collisional energy dissipation. The pressure drop along the pipe is nearly linear in the fully developed region, consistent with a constant friction factor. Within the investigated parameter space, designing pellets with moderately large ϕ and relatively small ζ improves conveying safety and reduces hydraulic energy consumption, providing practical guidance for feed pellet and pipeline design in marine aquaculture.