Experimental and Computational Study of Pattern Formation in Periodically Pulsed Gas-Solid Fluidized Beds

Despite great efforts to understand the chaotic dynamics of fluidized beds, the unpredictable behaviour of these reactors still complicates their design, control and scale-up. Fluidized bed engineering would be considerably simplified by forcing the bed to behave in a more predictable manner.

More than a decade ago, Coppens et al. [1, 2] demonstrated experimentally that a periodic flow could induce the formation of regular patterns in gas-solid fluidized beds: in quasi-2D beds, bubbles rise forming hexagonal configurations with a pitch that seems independent of bed width. In shallow 3D beds, the patterns formed on the surface resemble those observed in vibrated granular media. In spite of the potential of this phenomenon, little progress has been achieved:  pattern formation in fluidized beds is far from being understood and the experimental conditions to observe it are unclear. Moreover, Computational Fluid Dynamics (CFD) have not been able so far to clearly reproduce the experimental patterns, even though discrete element model (DEM) studies by Wang and Rhodes suggest some organization of the bubbles [3].

In this contribution, we discuss our recent insights about pattern formation in fluidized beds by facing the problem on three fronts: experimentally, theoretically and with CFD.

References:

[1] M.-O. Coppens, M.A. Regelink and C.M. van den Bleek, World Conference in Particle Technology (2002).

[2] M.-O. Coppens and J.R. van Ommen, Chem. Eng. J. 96, 117-124 (2003).

[3] X.S. Wang and M.J. Rhodes, Powder Techn. 159, 142-149 (2005).