Behavior and Properties of Bubble-Free Fluidization

Recently, McLaren et al. (PNAS, 2019) reported gravitational instabilities occurring in gas-fluidized beds consisting of light and heavy particles vibrated vertically so as to enable particle motion without gas bubbles rising through the system. This “bubble-free fluidization” state is somewhat different from the bubbling fluidization and homogeneous fluidization states conventionally seen in gas-fluidized beds, since bubbles do not drive particle convection and the bed volume does not expand significantly beyond packed bed conditions. Here, we investigate the convective, diffusive and rheological properties of this bubble-free fluidization state using imaging experiments and computational modeling.