4.1. Effect of liquid velocity
Most liquid fluidized beds operate in the particulate fluidization
regime. However, with high density particles, it is possible to reach
the bubbling fluidization regime, where particle-free voids or
“bubbles” are formed. However, in all of the velocities applied in
this work the fluidized bed was in particulate fluidization regime.
Fig. 8 shows the effect of liquid velocity on the t90 for stainless
steel particles filled in the column. As can be seen from this figure
t90 decreases sharply in the fixed bed regime but after minimum
fluidization condition there are no considerable difference between
t90 values at different liquid velocities.
In the fixed bed regime the bed voidage remains is approximately
constant and by increasing the liquid velocity the Nusselt
number value rises. Whereas, at the fluidized bed regime although
the Nusselt value growths by increasing the liquid velocity the
voidage of the bed rises too and according to eq. (12) the very steep
curve of t90 in the fixed bed regime is changed to a cure with very
gradual slop for the fluidized state.