Granular particles, such as sand or catalyst, are ubiquitous in nature and industry, and the complexity of granular flows continues to confound physicists, geoscientists, applied mathematicians and engineers. In heterogeneous catalytic reaction processes, packed beds and fluidized beds are two most widely used reactors and both of them involve gas flow through granular particles. In packed beds, particles are kept stationary and thus local hot spots can form, although the gas-solid contact efficiency is maximized. In fluidized beds, particles are suspended in a fluid-like state with heterogeneous gas bubbles rising, which promotes heat transport while also creates difficulties in scale-up due to mathematically chaotic bubble motions. Recently, we found that by combining both gas flow and vertical vibration, structured flow patterns including structured convection cells, structured surface waves, and structured bubbling can be formed at some specific conditions. Within the structured convection cells and surface waves, particles can move in a densely packed yet fluidized state without significant gas bubbles traveling through the particles, creating the best aspects of both packed beds and fluidized beds, while avoiding their detractions. Within the structured bubbling pattern, the otherwise chaotic bubble dynamics in conventional fluidized beds can be transformed to a highly predictable triangular pattern, in which bubbles of uniform size form and rise without coalescing or splitting, simplifying the scale-up of fluidized beds. Overall, these found structured flow patterns provide a potentially new way to address the problems of the currently-widely-used heterogeneous catalytic reactors. Based on numerical simulations, the mechanisms underlying different structured flow patterns were uncovered.
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