On the effective viscosity of suspensions

This work discusses the classical problem of effective viscosity of a Newtonian fluid with rigid spherical particles. It argues that the simple non-interaction approximation when formulated correctly yields an effective viscosity ratio for the suspension in the form μ/μ₀ = (1 − 2.5?)⁻¹ that remains accurate at much higher volume fractions of particles ? than the usual first-order approximation μ/μ₀ = 1 + 2.5?.