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 − 2.5ϕ)−1 that remains accurate at much higher volume fractions of particles ϕ than the usual first-order approximation μ/μ0 = 1 + 2.5ϕ.