Effects of large particles on the transport characteristics of slurries in horizontal pipes

To explore the microscopic effects of adding large particles on the transport characteristics of slurries in horizontal pipes, especially the reason why the pipeline resistance can be significantly reduced under certain working conditions, we simulated and compared the transport characteristics of a glass sphere slurry with a uniform particle size of 0.125 mm, before and after addition of the same particle volume fraction of 0.44-mm glass spheres at different flow rates and different solid-volume concentrations. The effects of the addition of large particles on the transport characteristics of small particles under different flow conditions, including the solid-volume concentration distribution, particle velocity distribution, granular pressure, turbulent kinetic energy of the small-particle phase, and wall shear force were studied. The adition of large particles was found to increase the granular pressure, decrease the turbulent kinetic energy of the small-particle phase, significantly reduce the wall shear force of the small particles, and reduce the total pipe resistance (by ∼10%) at flow velocities of 4 m/s and solid-volume concentrations of 20%, while under other conditions, especially at flow velocities of 2 m/s, the addition of large particles significantly increased the total pipe resistance. In addition, the mechanism and characteristics of the resistance reduction achieved by the large particles were examined from the perspective of reduced turbulence intensity. The results offer insights for a greater understanding of the resistance reduction mechanism and characteristics of graded slurry.