A new definition of bed expansion index and voidage for fluidized biofilm-coated particles

Experimental data available in the literature for bed voidage and bed expansion index of biofilm-coated particles in a fluidized bed was extracted, sorted and used to study the validation of the proposed bed expansion index equations in the literature. Drag coefficients of biofilm-coated particles for all the aforementioned data were calculated using a new proposed equation [1] that describes drag forces as a function of Archimedes numbers. Archimedes number was proposed to be superior to Reynolds number for bed expansion definition. New equations based on Archimedes number and physical properties of biofilm-coated particles were proposed to calculate the bed expansion index of fluidized biofilm-coated particles as well as bed voidage in fluidized bed bioreactors. The new equations predicted the existing experimental bed expansion index and voidage with less standard average error than all other literature equations that related bed expansion to Reynolds number.

► The validity of all literature bed expansion index (n) correlations for bioparticles was studied.
► In validation, the newly proposed drag coefficient equation based on Ar (AIChE 2010) was considered.
► A new equation for (n) based on Ar of bioparticles and their physical properties was proposed.
► The new equation predicted the experimental n and voidage more accurately than those in literature.
► The new equation is an explicit function of settling velocity and avoids trial and error calculation.