Physical modelling of colloidal slurry flows

Abstract

The study looks at the rheology and pipeline flow properties of colloidal suspensions dispersed in electrolytes of different concentration and type. Fuso silica spheres (0.8pm) form the dispersed phase of the suspension, and KN03, KCI electrolytes the continuous phase. The strength of the particle-particle interaction is significantly influenced by the electrolyte concentration. An increase in the electrolyte concentration from 10 4M to IM results in the formation of aggregates, thus influencing the sedimentation, sediment bed structure and pipeline transportation properties. Silica aggregates formed in IM electrolytes are on average 5.75 times bigger than the primary particle. Pipeline transportation studies have shown the aggregated suspension to have a lower minimum transport velocity than the dispersed suspension. Such behaviour is believed to be related to interfloc flows within the aggregate, enhancing the level of fluid turbulence. The centre-line and near wall turbulence intensities are enhanced in the presence of aggregates, while dispersed suspensions have negligible effect on modulating the fluid turbulence. Measurement of the streamwise RMS shows two critical Reynolds numbers with increasing flow velocity. The first critical Reynolds number (Re = 5500) occurs when the RMS profile of the aggregated suspension diverges (exceeds) from the RMS profiles of the dispersed and single phase flows. This enhancement is thought to be related to interfloc flows. A second critical Reynolds number (Re = 8000) is identified when the RMS profile of the aggregated suspension begins to converge with the dispersed and single phase RMS profiles. Convergence of the RMS profiles is related to the break-up of aggregates once a critical fluid shear stress is exceeded. Aggregate break-up data is verified with results collected using a Bohlin CVO-R rheometer