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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. [ABSTRACT FROM AUTHOR]

The different slurry transport properties in horizontal pipeline are investigated using a steady three-dimensional hydrodynamic model based on the kinetic theory of granular flow. The flow velocity and solid concentration distributions of slurry transported by pipeline and their regularly changing trends with varying pipe diameter (D = 51.5, 54.9, 103, 263, and 495 mm), solid volume concentration (Cvf = 20%, 30%, 40%, and 50%), grain diameter (dp = 0.09, 0.125, 0.165, 0.27, and 0.44 mm) and flow velocities (v = 2, 3, 4, and 5 m/s) are studied. The simulation result shows that under heterogeneous regime, fine particles, smaller than the sum of thickness of the viscous sublayer and buffer layer are most concentrated toward the pipe bottom (maximum concentration at the relative location ymax ≈ 0.02 D) while the greatest concentration of coarser particles is away from the pipe bottom (ymax ≈ 0.1 D). The results obtained in this work provide a solid foundation for further study of the resistance mechanism and pipe wear and can be used as a reference for analyzing the mesoscopic processes of slurry transport by pipeline. [ABSTRACT FROM AUTHOR]

The existing formulas for calculating the pipeline transport resistances of granular materials are mostly based on the experimental data for single-sized or regularly graded particles. Consequently, it is necessary to simplify the in-situ distribution using an equivalent size, such as the median particle size (d50), arithmetic mean size (dm), or harmonic average size (dk), in the sediment transport resistance calculations. This simplification completely ignores the effect of particle gradation on the pressure drop, particularly in the case of multi-size, high-concentration particle transport. Therefore, the mechanism and degree of influence of the particle size variation in different flow conditions on the pipeline resistance was investigated in this study. The interaction between the differently sized particles in the graded slurry was also examined. Furthermore, a new model called the Shanghai Jiao Tong University high-concentration multi-sized slurry pressure drop (SJTU-HMSPD), which is based on the particle size distribution and multi-regime slurry resistance in pipeline transport throughout the flow velocity range, was developed and is presented in this paper. The SJTU-HMSPD is more suitable for calculating the pipeline transport resistances of complex graded slurries, and the calculation results agree well with the experimental data. All the input data are available in practice making the model very convenient. [ABSTRACT FROM AUTHOR]

Resistance reduction has always been a concerning problem in pipeline transportation projects. Moreover, adding fine particles has shown resistance reduction. Therefore, we studied the effect of adding finer particles on the transport characteristics of coarse-particle slurries in pipelines. The flow conditions and slurry characteristics, such as the flow velocity and particle volume concentration, and the addition of finer particles can reduce the resistance of coarse-particle slurries under certain working conditions. In this study, the changes in the transport characteristics of slurries with 0.44 mm diameter glass balls after adding an equal volume of 0.125 mm diameter glass balls under different flow velocities and volume concentrations were analysed. The effects of adding fine particles on the transport characteristics of coarse particles under different flow conditions were determined, including the distributions of the particle volume concentration, velocity, particle pressure, and wall shear stress. We observed that adding fine particles could change the flow regime of coarse particles near the critical flow velocity (from sliding bed to heterogeneous flow), thereby considerably reducing the pipeline resistance (by approximately 20%). At a high flow velocity (heterogeneous or homogeneous flow), the addition of fine particles will increase the resistance. The study results explain the mechanism and characteristics of resistance reduction on adding fine particles from the perspective of changing the flow regime. These findings can serve as a reference for further studying the resistance reduction mechanism on adding fine particles and for finding the optimal particle size distribution for slurry transport in pipelines. • The addition of finer particles on coarse-particle slurry in pipelines is studied. • The mechanism of resistance reduction by adding finer particles is identified. • Resistance reduction effect by adding finer particles is evaluated. • Findings show insights on optimal particle sizes for slurry transport in pipelines. [ABSTRACT FROM AUTHOR]