Rheology of suspensions of spherical particles in a newtonian and a non-newtonian fluid

Abstract

Properties of suspensions of spherical glass beads (25–38 μm dia.) in a Newtonian fluid and a non-Newtonian (NBS Fluid 40) fluid were measured at volume fractions, φ, of 0%, 10%, 20% and 30%. Measurements were made using a modified and computerized Weissenberg Rheogoniometer. Properties measured included steady shear viscosity, η( γ . ), first normal stress difference, N 1( γ . ), linear viscoelastic properties, η′(ω) and G′(ω), shear stress relaxation, σ − ( γ . , t), and growth, σ +( γ . , t) and normal stress relaxation, N 1 −( γ . , t). For a the Newtonian fluid, increasing φ causes both η and η′ to increase, with η′ showing a slight frequency dependence. Both N 1 and G′ are zero and stress relaxation and growth occur essentially instantaneously. For the NBS fluid, both η and η′ increse with φ at all γ . and ω, respectively, the increase being greater as γ . and ω approach zero. N 1 and G′ are less affected by the presence of the particles than η and η′ with the effect on G′ being more pronounced than on N 1. For fixed γ . , stress relaxation and growth exhibit greater non-linear effects as φ is increased. A model for predicting a priori the linear viscoelastic properties for suspensions was found to yeild reasonable estimates up to φ = 20%.