Rheology of concentrated suspensions and their settling characteristics in vessels having inclined walls. Final report

Technical Report · Tue May 01 04:00:00 EDT 1979

DOI:https://doi.org/10.2172/6216906· OSTI ID:6216906

Acrivos, A.

A fundamental investigation is presented of two subjects involving the behavior of solid particles suspended in Newtonian liquids: enhanced sedimentation in vessels having inclined walls, and, the rheology of concentrated suspensions. A theory developed for enhanced sedimentation is based on principles of continuum mechanics. The resulting equations are solved analytically using asymptotic techniques, and simple expressions, containing no adjustable constraints, are derived for the settling rate and for the resulting flow pattern within the suspension and within the clear fluid. It is shown that the Ponder--Nakamura--Kuroda expression for the enhancement applies if the flow is laminar and if the dimensionless number ..lambda.. - a ratio of a sedimentation Grashof number to a sedimentation Reynolds number - is large. The latter condition is always met in practice and in most laboratory experiments. Also, for values of H/b of order ..lambda../sup 1/3/ or larger, the present theory predicts the existence of a new type of settler operation not reported previousy. All the predictions of the theory were found to be in excellent agreement with experiments. Suspensions of solid particles in Newtonian liquids have historically been viewed as Newtonian fluids having an effective viscosity eta/sub s/ which is a function only of phi, the solids concentration. This has been particularly the case when the particles are monodispersed solid spheres large enough for non-hydrodynamic effects to be negligible. If phi exceeds 30% such suspensions are no longer isotropic Newtonian fluids. Then the concept of an effective viscosity no longer applies: a fact consistent with the large scatter in the effective viscosities experimentally determined by previous investigators. A new constitutive equation was therefore developed which treats the suspension as a fluid with structure and which accurately modeled our experimental data.

• Research Organization: Stanford Univ., CA (USA). Dept. of Chemical Engineering
• OSTI ID: 6216906
• Report Number(s): EPRI-AF-1085
• Country of Publication: United States
• Language: English

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