Modelling high concentration settling slurry flows

Abstract

lurry flows are encountered frequently in the chemical process industries and one of the simplest methods of classification is based S upon the tendency of the slurry to segregate or "settle" in the quiescent state. Non-settling slurries are composed of fine particles and are usually flocculated. The floc interaction which generates the internal structure that prevents settling is also responsible for the non-Newtonian behaviour which is commonly observed with these slurries. Satisfactory prediction of pipeline friction can usually be achieved for these slurries in both laminar and turbulent flow, using models which assume the slurry is a continuum.Slurries of particles which are too coarse to flocculate usually approximate Newtonian behaviour, so that the ratio of slurry viscosity to that of the carrier fluid can be considered as a function of particle shape and solids concentration. The effect of particle shape is sometimes taken into account by including the maximum settled concentration, C , , , , , as a parameter in correlations for relative viscosity. One equation describing this effect for sand grains with C, , , , , near 0.63 is (Cillies et al., 1999):where C is the solids volume fraction. At high solids concentrations, where the last two terms become important, particle-particle interactions are considered to play a major role in energy dissipation when the slurry is sheared in laminar flow. Recent experimental studies of sand transported by liquids of high viscosity have indicated that these interactions provide the mechanism for particle suspension in laminar flow (Cillies et al., 1999). For slurries of coarse particles, i.e., "settling" slurries, the frictional processes are fairly complex, especially when the flows are turbulent. Energy losses for flows of these settling slurries have been considered by many researchers to be a combination of kinetic (fluid-like) and Coulombic (velocity independent) friction. However a paradox is introduced by the fact that slurry viscosity does not appear to be an important parameter in kinetic slurry friction, at least at low and moderate solids concentrations. Spells (1 955) has given an equation for estimating the velocity above which pressure gradients can be calculated from a "homogenous" rule of thumb using the slurry density and the carrier fluid viscosity. Although predictions from Spells' equation are not particularly useful, the asymptotic high velocity behaviour which he described was confirmed at concentrations below about 30% to 35% solids by volume in horizontal flow by Cillies et al. (1 991).

Assessing Eulerian–Lagrangian simulations of dense solid-liquid suspensions settling under gravity

“…Other applications are sediment transport (e.g. in environmental flows [2]), catalytic slurry reactors [3], and hydrotransport in the mining industries [4]. Crystallization processes are often carried out in agitated tanks operated under turbulent conditions with high solids loading (20% solids by overall volume is not exceptional).…”

Modeling of sand-water slurry flow through horizontal pipe using CFD

“…From then, many researches took place aiming at predicting concentration distribution for slurry flows. A few notable of them are Shook and Daniel (1965), Shook et al (1968), Karabelas (1977), Seshadri et al (1982), Roco and Shook (1983), Roco and Shook (1984), Gillies et al (1991), Gillies and Shook (1994), Gillies et al (1999), Gillies and Shook (2000), Kaushal and Tomita (2002), Kaushal and Tomita (2003) and Kaushal et al(2005). Apart from this, several studies for predicting pressure drop over the length also took place for slurry flows.…”

Effect of a Symmetric Contraction on the Concentration Profiles of a Particle-Laden Slurry

“…For constant fluid rheological parameters, size of the particles (d p ), and pipe diameter (D), the deposition velocity (V d ) can be defined as the mean velocity of the continuous phase at which the particles start to settle at the bottom of the pipe under the action of gravity. Resuming the discussion on concentration profiles, it is worth mentioning at this point that the concentration variation in relation to changes in the type of fluid, particle diameter (d p ), and different pipe diameters (D) has been extensively dealt with by Roco andShook (1984), Schaan et al (2000), Gillies and Shook (2000), Gillies et al (2004), and Kaushal and Tomita (2007). Roco and Shook (1984) performed a thorough experimental analysis by varying all the parameters that were mentioned previously, and derived empirical relations that would predict the contractions has hardly been documented.…”