Numerical Investigation of Hydraulic Transport Characteristics in a Vertical-to-Horizontal Elbow for Deep-Sea Mining

Hydraulic transport through pipeline bends can redistribute particles and alter the pressure response in deep-sea mining lifting systems. This study examines coarse-particle transport through a vertical-to-horizontal elbow using a two-way coupled CFD–DEM framework. The framework is benchmarked at the component level against published horizontal-pipe, vertical-pipe, local particle-transport, and elbow pressure-drop data. We examine how feed concentration, particle diameter, particle gradation, and particle density affect local particle concentration, particle velocity, slip velocity, and pressure response. Under the investigated conditions, time-averaged local particle concentration generally exceeds feed concentration, indicating solids holdup within the monitored regions. A concentration minimum occurs within 2–3 pipe diameters downstream of the elbow, where bend-induced particle acceleration temporarily reduces local solids holdup. Feed concentration and particle density produce the largest changes in the apparent hydraulic gradient. Particle diameter and gradation have weaker effects at the tested mixture velocity of 3 m/s. Broader gradations reduce the downstream increase in local concentration and the attenuation of particle velocity. These results describe simulated transport trends across the vertical–bend–horizontal transition under the operating conditions studied.