A Phase Map for Vertical Upflow of Slightly Cohesive Geldart A Powders Focused on High Solids Mass Flux

Flow regimes of vertical upflow for slightly cohesive Geldart A powders at high solids mass flux (Gs≳ 500 kg/m2s) are not fully resolved. In particular, Dense Suspension Upflow (DSU) as a distinct flow regime and its transition boundaries are not broadly accepted. Furthermore, the locus of the pressure gradient minimum, which is the broadly accepted dense–dilute transition at low Gs, requires validation at high Gs. In our recent work, by adapting the phase map of Wirth and by Eulerian modeling, DSU was defined as a distinct flow regime with gross upflow of solids and with granular temperature at the wall greater than that in the bulk. This study has further validated the definition of DSU and its transition boundaries by extending the modeling to areas not fully explored in the earlier work. Furthermore, this study has identified (a) the possibility of a phase of DSU between fast fluidization and turbulent regime at all Gs; and (b) the need to review the suitability of the locus of the pressure gradient minimum as the dense–dilute transition at high Gs. Additionally, our work has demonstrated (a) a new provisional correlation that the upper transport velocity for Geldart A powders is significantly greater than hitherto predicted; and (b) the slip velocity in the transport regimes increases with Gs to peak within fast fluidization and falls thereafter to attain low multiples of the terminal settling velocity within DSU.