Rheology of Non-Brownian Suspensions

Suspensions of non-Brownian particles are commonly encountered in applications in a large number of industries. These suspensions exhibit nonlinear flow behavior, even in Newtonian suspending fluids under conditions where inertial effects can be ignored and linearity would normally be expected. We review the observed rheological behavior, emphasizing concentrated suspensions of spheres in Newtonian fluids, and we examine both particle-level and continuum approaches to describing the nonlinear behavior. Particle-particle nonhydrodynamic interactions appear to be important in concentrated suspensions. Continuum descriptions are not yet adequate to describe the observed behavior.