Oak Ridge National Laboratory
Knoxville TN 37932-6472
C.E.A. Finney, K. Nguyen
University of Tennessee
Knoxville TN 37996-2210
Morgantown Energy Technology Laboratory
Morgantown WV 26507-0880
Recent studies of slugging in beds of Group D particles have demonstrated apparently low-dimensional dynamical patterns with strong similarities to deterministic chaos. It has been conjectured that these patterns result from a macroscopic self-organization of the particles that produces unstable nonlinear oscillations of varying complexity. It has also been demonstrated that the nonlinear instabilities can be exploited to either enhance or diminish the slugging using small gas pulses that are injected using an appropriate feedback injection scheme.
We present a simple model which captures many experimentally observed features for Group D slugging. The model utilizes a simple iterative function relating each bed oscillation to succeeding oscillations. In addition to providing a means for making on-line control decisions, the model provides insight into the granular-flow physics that are involved. We derive the model based on physical arguments and compare its predictions with laboratory experimental data. We show that despite the model's simplicity, it agrees well with observations and provides a means of correlating slugging data.
Additionally, we illustrate how our model explains chaotic features observed in slugging beds. We show that dynamic patterns are produced by interaction of nonlinear drag forces and stochastic perturbations of bed parameters. This interaction of deterministic and stochastic elements produces patterns sometimes referred to as "noise-induced chaos" or "noisy chaos" which is similar to, but subtly different from, the classical paradigm of deterministic chaos. We believe that noisy chaos may be more generally relevant for the characterization of fluidized beds.
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Updated: 2001-05-16 ceaf