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Experiments have been performed to test the efficiency with which a novel fluidised bed technique could separate different metallic powders in terms of size and density. The overall aim was to assess the potential of this technique for the commercial separation of defective powder fractions from mechanically alloyed (MA), iron based powders. Separation in terms of size was readily achieved, with the largest powder particles sinking to the bottom of the fluidised bed. In a simulated commercial process, density separation of defective Fe3Al powder could not be demonstrated as any differences in density were overshadowed by size and morphology differences. However, from a batch of iron based powder (ρ=8·02 g cm-3), seeded with six other metallic powders, aluminium powder (ρ=2·70 g cm-3) segregated strongly to the top of the bed from where samples containing 93 vol.-%Al were taken. The process is thought to be sensitive to differences in density of a factor of 1.1–3. [ABSTRACT FROM AUTHOR]

The dispersion of pulses of a range of shapes through a bubbling fluidized bed has been studied using an ECAT EXACT HR+ PET camera. The equipment and materials used made it possible to label actual bed particles with a radioactive labeler for use as tracer. The experimental equipment and procedure as well as the data analysis procedure are described. The results are shown as bitmaps, 3-D plots, and contour plots of the relative tracer concentration during 1-s time intervals. The particle pulse is shown to exhibit a cyclical axial motion while it is being dispersed. The results are compared with a phenomenological stochastic model for particle dynamics. It is further shown that the model, which is based on the notions of upward material transport with the fluidization bubbles and material descent with dispersion in the bulk, qualitatively captures all the essential features. Material transport only in bubble wakes, however, could not account quantitatively for the results. The discrepancy is likely attributable to "gulf streaming" in the bed, a phenomenon that should be studied experimentally and accounted for in models for particle dynamics in fluidized beds. [ABSTRACT FROM AUTHOR]