Self-organization and chaos in a fluidized bed

We present experimental evidence that a complex system of particles suspended by upward-moving gas can exhibit low-dimensional bulk behavior. Specifically, we describe large-scale collective particle motion referred to as slugging in an industrial device known as a fluidized bed. As gas flow increases from zero, the bulk motion evolves from a fixed point to periodic oscillations to oscillations intermittently punctuated by "stutters," which become more frequent as the flow increases further. At the highest flow tested, the behavior becomes extremely complex ("turbulent").