Numerical simulation on transportation behavior of gradated coarse particles in deep-sea vertical pipe transportation

Flow pattern and hydrodynamic characteristics of coarse particles in deep-sea hydraulic lifting pipes are simulated using a numerical approach developed by combining the computational fluid dynamics method with a discrete element method in the Euler–Lagrange framework. This paper examines the effects of feed concentration, two-phase flow initial mixture velocity, and particle gradation on the dynamic characteristics of particles and flow pattern in the pipe by validating the rationality of numerical simulation. The results demonstrate that particles are distributed from the pipe center to the pipe wall, while the lift force causes more particles to be distributed in the pipe center. Moreover, greater inertia makes large particles more concentrated in the center. Particle-induced turbulence modifies the lift force and causes particles to move from the pipe center to its wall. Due to the increasing trend of lift force, particles gather toward the center of the pipe at an increasing pace as the initial velocity increases. The greater the feed concentration, the more particles disperse toward the pipe wall due to the violent momentum exchange caused by the high concentration and the significantly altered lift force caused by the high turbulent kinetic energy resulting from a high concentration. From the particle gradation 1:1:1 to 1:6:1, the pressure drop decreases gradually as the reduction in small particles decreases the number of particles near the wall, and the frictional energy loss between the particles and the pipe wall decreases.