2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/216258We present a model including diffusion and particle-size dispersion for separation of particles in deterministic lateral displacement devices also known as bumper arrays. We determine the upper critical diameter for diffusion-dominated motion and the lower critical diameter for pure convection-induced displacement. Our model explains the systematic deviation, observed for small particles in several experiments, from the critical diameter for separation given by simple laminar flow considerations.5 pages, 3 eps figures, revtex4Fluid DynamicsComputational Physicstext