Bubble self-organization in pulsed annular gas-solid fluidized beds

Pulsating the gas flow in rectangular, quasi-2D fluidized beds can turn the chaotic bubble flow into a regular bubble pattern. Bubbles form a rising triangular lattice, leading to a scalable flow structure with controllable properties, such as narrow bubble size distribution, distance between bubbles, and residence time. This overcomes challenges encountered in conventional units, like flow maldistribution and non-uniform contact. In this work, we reproduced a similar, dynamically structured flow in a cylindrical annular geometry. Regular bubble patterns emerge along the circumference of the cylinder. The absence of lateral walls and strongly curved boundaries could cause instabilities. This study presents an operating window for creating spatiotemporally structured flows and compares the flow properties in quasi-2D rectangular and annular systems, quantifying the impact of curvature and, effectively, lateral walls on flow behavior. These insights offer new opportunities for modularization of fluidized bed operations.