Numerical study on coarse granular flow and performance characteristics of the Coanda effect-based collector for deep sea mining

The application of the Coanda effect-based method for harvesting polymetallic nodules from the seafloor is a sophisticated technique in underwater exploitation. The primary objective of this paper is to investigate the influence of the non-dimensional curvature radius (h/R) of the jet flowing against the wall on the lift capacity of the Coanda effect-based collector. A computational fluid dynamics approach coupled with the discrete element method is proposed and validated. The high-speed curved jet entrains seawater from the bottom clearance to prevent sediment erosion, resulting in an up-wash flow along the collector tube. The adverse pressure gradient and the impinging kinetic energy of the jet are two factors that provide lift force for the manganese nodules. As the value of h/R increases, the wall becomes more curved, resulting in a larger jet half-width and faster energy diffusion along the jet wall, which gradually dominates the movement of particles. The collection rate for the case with h/R = 0.028 (91.4 %) is slightly higher than that for h/R = 0.0145 (91.8 %), while both cases are higher than that for h/R = 0.0459 (90.3 %). As h/R increases, the lifted particles exhibit sharper trajectories at the particle separation position, leading to reduced collection efficiency.