LIQUID-PHASE MIXING IN EXTERNAL-LOOP AIRLIFT BIOREACTORS

Mixing time, circulation time and downcomer linear liquid velocity wer e measured in two sizes of external-loop airlift bioreactors with Newt onian and non-Newtonian fluids. The mixing time increased as a result of an increase of non-Newtonian characteristics. However, the liquid c irculation time was affected only slightly by non-Newtonian flow behav ior. A semi-empirical correlation for circulation time in external-loo p airlift bioreactors was proposed. The proposed correlation was compa red with the present experimental results and those in the literature. Reasonable agreement was obtained between the predicted and experimen tal values of circulation times. The downcomer liquid velocity was alm ost independent of the downcomer-to-riser cross-sectional area ratio. The correlation based on the concept of an eddy diffusivity predicted downcomer liquid velocities in Newtonian and non-Newtonian fluids.