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Abstract
The influence of a pseudoplastic non-Newtonian fluid upon the hydrodynamic performance and mixing parameters of a concentric tube air-lift fermenter has been studied using a range of dilute xanthan gum solutions (0-0.5% weight by volume). Liquid circulation times vary in a complex pattern with increasing gum concentration. At low concentrations, circulation was more; rapid due to drag reduction whilst at the highest concentrations circulation times were increased. The column voidage decreased with increasing gum concentration and bubbly flow in the riser was replaced by slug flow. For all gum concentrations the effective dispersion coefficient for a single passage around the loop was increased relative to tap water. An improved radio-pill flow follower system for hydrodynamic studies is described.