Hydrodynamic particle volume and fluidized bed expansion

Particulate fluidized bed expansion may be described by the Richardson‐Zaki equation, \documentclass[article]\pagestyle[empty]\begin[document]$ \frac[u][[u_i ]] = e^n $\end[document] The values of n for very fine and/or aggregated particles and for particles of irregular shape are often found to be larger than those for comparable spherical particles. Previous work on aggregated systems by one of the authors showed that a modified Richardson‐Zaki equation, \documentclass[article]\pagestyle[empty]\begin[document]$ \frac[u][[u_i ]] = \left( [1 - KC] \right)^n $\end[document] (where C = 1‐ε), provided a more consistent correlation of the data. The parameter K accounted for the effective hydrodynamic volume of the particles during fluidization and the application of this concept to non‐spherical particles was the subject of the present study. While K for spherical particles was essentially equal to unity, values from 1.17 to 1.43 were found for equidimensional but irregular particles with considerably higher values for flat particles. An equation relating K to particle shape is offered which, when combined with the Richardson‐Zaki relationships, provides a more accurate prediction of the expansion behaviour of non‐spherical particles.