Oak Ridge National Laboratory
Knoxville TN 37932-6472
C.E.A. Finney, K. Nguyen
University of Tennessee
Knoxville TN 37996-2210
We focus on dynamic slugging transitions in gas-fluidized beds of Geldart Group D particles as gas flow is varied. Our results are based on high-speed measurements of pressure drop and particle motion in a 10.2-cm-diameter bed operating at ambient temperature with air as the fluidizing medium. Our experimental solids are 4.5-mm-diameter steel and 2.9-mm-mean-diameter glass particles.
We demonstrate that our observations are consistent with viewing the large-scale bulk dynamics of the bed as a noisy but low-dimensional, nonlinear oscillator that undergoes transitions involving a fixed point, possibly two limit cycles, and chaotic motion. By constructing appropriate return maps of the bed dynamics, it is possible to characterize slugging transitions in terms of the formation and interaction of stable and unstable manifolds. The onset of chaos appears to occur through development of intermittent "stutters" in the slugging pattern.
We also show that the sensitivity of the slugging bed to small perturbations makes it possible to use chaos control algorithms to alter the bed behavior greatly. The resulting changes in bed operation can have important effects on heat- and mass-transfer efficiency.
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