(331a) Derek Geldat and the A/B Transition

Geldart’s 1972 paper [1] on classification of particles in terms of their fluidization characteristics is easily at or near the top of the most influential publications on the subject of fluidization.  According to his classification, group A particles manifest a small window of stable bed expansion upon fluidization before bubbling sets in.  In contrast, Group B particles bubble immediately upon fluidization.  The boundary separating these two groups of particles, commonly referred to as the A/B transition, has been the subject of a great deal of research and controversy.  Several authors have attempted to explain the A/B transition as a manifestation of a stability boundary, while others have been critical of such studies; (for example see the review article by this author  [2]).  Experiments with particles of different sizes [3] suggest that the window of stable bed expansion becomes smaller and smaller as the particle size increases, which provides a simpler interpretation.

In this talk, the history of this debate will be reviewed.  Questions remaining about this A/B transition will be described.

References

[1] D. Geldart, Powder Technol., 7 (1973) 285.

[2] S. Sundaresan, Annu. Rev. Fluid Mech., 35 (2003) 63.

[3] P. N. Loezos, P. Costamagna and S. Sundaresan, Chem. Eng. Sci. , 57 (2002) 5123.