Experimental investigation for near-wall lift of coarser particles in slurry pipeline using γ-ray densitometer

Experimental data are collected in 54.9 mm diameter horizontal pipe for concentration profiles using γ-ray densitometer. Two sizes of glass beads with mean diameter and geometric standard deviation of 440 μm and 1.2 and 125 μm and 1.15, respectively, are used. These data are collected for flow velocity up to 5 m/s and overall concentration up to 50% by volume for each velocity. Experimental data measured by sampling probe and pressure gradients in the previous study D.R. Kaushal, K. Sato, T. Toyota, K. Funatsu, Y. Tomita, Effect of particle size distribution on pressure drop and concentration profile in pipeline flow of highly concentrated slurry, International Journal of Multiphase Flow, 31(7) (2005) 809-823.] are used to compare with γ-ray densitometer measurements and to study slip velocity and near-wall lift of particles in the pipeline. In overall, γ-ray densitometer and sampling probe give quite similar concentration profiles except for few cases of coarser (440 μm) particles at lower flow velocities. Measurements show that, for finer particles, point of maximum concentrations are near the pipe bottom (y/D = 0.1) and for coarser particles, maximum points are relatively away from the pipe bottom with decrease in shift as flow velocity increases. Pressure gradient profiles of equivalent fluid for finer particles are found to resemble with water data except for 50% concentration, however, more skewed pressure gradient profiles of equivalent fluid are found for coarser particles. Experimental results indicate absence of near-wall lift for finer particles due to submergence of particles in the lowest layer into the viscous sublayer and presence of considerable near-wall lift for coarser particles due to impact of viscous-turbulent interface on the bottom most layer of particles and increased particle-particle interactions. It is observed that near-wall lift decreases with increase in flow velocity; however, the effect of slip velocity on pressure drop is greater at lower flow velocities and less at higher flow velocities than near-wall lift of coarser particles in slurry pipeline. For finer particles, the departure from equivalent fluid pressure gradient profile at 50% concentration is attributed to the sudden increase of viscous sublayer thickness.