Hydromechanical stress is a crucial
parameter for a broad range
of multiphase processes in the field of (bio)chemical engineering.
The effect of impeller type and geometry on hydromechanical stress
in stirred tanks is important. The present study aims at characterizing
conventional and new impeller types in terms of particle stress. A
two-phase liquid/liquid noncoalescing dispersion system is employed,
and the drop breakage is monitored in-line in a stirred tank. The
published effects of agitation on drop deformation are confirmed and
expanded significantly for five modified new impeller types. Radial
impellers are advantageous for applications where low shear conditions
are desired. A modified propeller with a peripheral ring and the developed
wave-ribbon impellers present remarkable results by producing significantly
low and high hydromechanical stress, respectively. The results obtained
are correlated in terms of mean and maximum energy dissipation rate,
as well as circulation frequency in the impeller swept volume.
Mainly with respect to biotechnological cases, current developments in the field of impeller geometries and findings for multistage configurations with a specific view on aerated stirred tanks are reviewed. Although often the first choice, in the given case the 6‐straight blade disc turbine is usually not the best option. Furthermore, quantities usable for scale‐up, specifically applicable in this field are discussed. Only quantities taking local conditions into account appear to be able to actually compare different stirrer types and scales.
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