Flow pattern and pressure drop in highly concentrated slurries transportation pipelines were discussed. The particles are settling, and tend to settle down to the bottom of pipes due to the action of gravity force forming different flow patterns which can be indicated by particle concentration profile. Three distinct flow patterns can be observed for different particle size distribution at different velocities: fully stratified, partially stratified and fully suspended flow patterns. As for pressure drop, it is well known that pressure drops in pipeline flows of slurries are strongly dependent on the flow pattern developed in a pipeline. Furthermore, fine particles suspended in water make the water more viscous, and increase the friction. In case of coarse particles, having larger volume, they have the tendency to contact with the pipe wall and with the other coarse particles more times, which increase the friction of flow. Meanwhile, coarse particles are lifted by the pressure difference generated as they rotate in the liquid preventing the coarse particles from settling down which results in less friction. The mixture of particles of different sizes is helpful to reduce pressure drop in pipeline flow slurries. Narrow grading particles tend to have high frictional losses, while broad grading particles have low frictional losses at high concentrations.
Confined fluidization of fines in fixed bed of coarse particles