(223d) Conditions for Pattern Formation in Pulsed Fluidized Beds
Bringing in additional degrees of freedom provides the flexibility to manipulate the system hydrodynamics. In particular, pulsating gas-solid fluidized beds can lead to a unique fluidization state, where gas bubbles rise in a staggered way, forming regular patterns with a characteristic wavelength . Within a certain range of pulsed gas velocity, the bubble distribution and the physical properties can be effectively tailored by tuning the conditions of the inlet pulsed flow, such as the offset, pulsating frequency and amplitude. This phenomenon shows great potential to be applied as a non-intrusive method to structure the bed .
Despite its advantages, fundamental aspects underpinning pattern formation, such as energy dissipation and momentum transfer, have remained largely unexplored. Over the past years, a few modeling attempts have been conducted to investigate its underlying dynamics [4, 5], but with limited success. Only recently, we reported the first successful simulations capable of reproducing the pattern dynamics using a CFD-DEM (computational fluid dynamics â discrete element method) approach . These numerical results provide valuable physical insights into the fundamentals of fluidized bed dynamics.
In this presentation, we will discuss experiments on the formation and stability of regular patterns in 2D and 3D pulsed fluidized beds, subjected to various conditions and compare results with CFD-DEM numerical simulations. We present the impact of different pulsed flow conditions, particle physical properties, and bed depth on the pattern characteristics and regularity. A phase diagram is constructed to locate the pattern region and pointing out the favorable conditions for attaining patterns. We also discuss the propagation of the pattern structure in beds of different depth. By combining the experimental data with computational results, we interpret how the patterns propagate and are gradually disturbed when bubbles travel toward the bed surface, through analyzing gas and solid phase dynamics. These results are useful from a fundamental point of view, as well as for scale-up for applications.
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