Plenary Talk: Innovations in Fluidization, Inspired by Nature

Coppens, M. O., University College London
The non-uniform hydrodynamics of fluidized beds complicate their operation and scale-up. Over the past two decades, we have developed approaches that seek to structure bubbling fluidized bed hydrodynamics by drawing lessons from natural systems. A first example is a fractal injector, inspired by the structure of lungs and trees, to distribute fluids uniformly, promote local mixing, and preserve hydrodynamics over different length scales. A second example is pulsation of the gas flow, inspired by wave and wind-induced regular patterns on dunes and beaches, to organize a chaotic bubble flow into a regular, triangular tessellation of rising bubbles (deep, quasi-2D bed) or a square pattern (shallow, 3D bed) with controllable wavelength and bubble size, over a range of frequencies.

Simulations provide insights into the mesoscopic physics that induce the observed patterns by dynamic self-organization. Wave patterns in shallow beds display similarities with those observed in vibrated granular layers, although fluid-solid interactions lead to much richer behavior and qualitative differences as well, which are especially noted in the bubble patterns formed in deeper, quasi-2D beds. Common two-fluid models are unable to reproduce pattern propagation, because granular friction results in transitions in collective particle behavior between solid-like and fluid-like, during each pulsation period. On the other hand, discrete element model simulations, coupled with computational fluid dynamics, offer insights that do not only allow us to employ gas oscillation as a way to structure fluidized beds, but also to take pattern formation as a robust fingerprint to test computational models, which can be used to model and design fluidized beds more generally. Probing the rich behavior of pulsating fluidized beds helps us to augment our understanding of fluidization fundamentals. In this context, we are currently investigating annular beds, allowing us to study transitions in hydrodynamics between quasi-2D to 3D systems, which is essential in the application of this fascinating nature-inspired phenomenon to fluidized bed operation and design.