Abstract

Gas-solid fluidized beds have been shown to be consistent with deterministic chaos, and are appropriately termed a self-excited nonlinear system. The present study examines chaos suppression resulting from an opposing oscillatory flow in gas-solid fluidization. Recent studies of a new fluidization concept, termed pulse-stabilized fluidization, have shown promising results for heat transfer enhancement in fluidized bed combustors. Pulse stabilized fluidization is accomplished through a secondary flow that is oriented vertically downward in the fluidized bed, and is characterized by a mean and a sinusoidally oscillating component. This opposing oscillatory flow significantly alters the hydrodynamics of fluidization.

Chaos suppression may result from the systematic perturbation of a system variable or control parameter. In the present study, chaos suppression is demonstrated in the hydrodynamics of a bubbling fluidized bed through local instantaneous pressure measurements. Quantitative chaos measures are presented to demonstrate the degree to which chaos is suppressed in the fluidized system under specific operating conditions. The chaos, which is clearly suppressed in the pressure time-series data, is at times distinctly different from measured instantaneous heat flux data under the same operating conditions. Entropy values determined from phase-space attractors are contrasted between pressure and heat flux data to infer aspects of the physics.

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