The invention provides a device for separating a first entity and a second entity by flowing them downwardly in an inclined settling chamber. Each entity has its own outlet located at approximately the lowest end of the inclined settling chamber. The device may be used in industrial fields such as pharmaceutics, biologics, and biofuels, for the purposes of large-scale growth and separation of algae biomass, bacteria and yeast cultures; algae metabolite production; and cell separation, among others. The invention exhibits technical merits such as effective particle separation or concentration capacity, robust structure, easy operation, cost-effective manufacturability, disposability, and high productivity in e.g. perfusion photobioreactor systems.