Settling devices for separating particles from a bulk fluid with applications in numerous fields. The particle settling devices include a first stack of cones with a small opening oriented upwardly or downwardly. Optionally, the settling devices may include a second stack of cones with a small opening oriented downwardly or upwardly. The cones may be concave or convex. These devices are useful for separating small (millimeter or micron sized) particles from a bulk fluid with applications in numerous fields, such as biological (microbial, mammalian, plant, insect or algal) cell cultures, solid catalyst particle separation from a liquid or gas and waste water treatment.