(22a) Linking Bubble Characteristics and Species Segregation in Bubbling Gas-Fluidized Beds

Low-velocity, bubbling, gas-fluidized-bed experiments involving Geldart Group B particles with continuous size distributions have been carried out, with a focus on obtaining (i) axial concentration profiles and (ii) axial bubble profiles. The system of interest is Geldart Group B particles, namely, sand of various widths of Gaussian or lognormal distributions. Similar to previous works on binary systems, segregation results show that mean particle diameter decreases with increasing bed height, and that wider Gaussian distributions show increased segregation extents. Surprisingly, however, lognormal distributions exhibit a non-monotonic segregation trend with respect to distribution widths. Given the widely accepted view of bubbles as ?mixing agents', the initial expectation was that bubble characteristics for lognormal distributions would be similarly non-monotonic. Surprisingly, the results show that measured bubble parameters (frequency, velocity and size) increase monotonically with increasing width of PSD's for all continuous distributions examined (Gaussian and lognormal). A closer inspection of the data reveals a bubble-less region at the bottom of the bed for the segregated systems, despite the entire bed being fully fluidized. More specifically, results indicate that regardless of the magnitude of the bubble parameters, the larger the bubble-less layer is, the more segregated the system becomes. The direct comparison between experimental bubbling and segregation patterns performed here provides a more complete physical picture of the link between the two phenomena.