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Keywords:

  • bubbling gas-fluidized bed;
  • axial bubble profile;
  • continuous particle-size distribution (Gaussian, lognormal);
  • Geldart Group B;
  • segregation

Abstract

Experiments involving a bubbling, gas-fluidized bed with Gaussian and lognormal particle-size distributions (PSDs) of Geldart Group B particles have been carried out, with a focus on bubble measurements. Previous work in the same systems indicated the degree of axial species segregation varies non-monotonically with respect to the width of lognormal distributions. Given the widely accepted view of bubbles as “mixing agents,” the initial expectation was that bubble characteristics would be similarly non-monotonic. Surprisingly, results show that measured bubble parameters (frequency, velocity, and chord length) increase monotonically with increasing width for all PSDs investigated. Closer inspection reveals a bubble-less bottom region for the segregated systems, despite the bed being fully fluidized. More specifically, results indicate that, the larger the bubble-less layer is, the more segregated the system becomes. The direct comparison between bubbling and segregation patterns performed provides a more complete physical picture of the link between the two phenomena. © 2011 American Institute of Chemical Engineers AIChE J, 2011