Abstract
Mixing time (θ) was measured in a 45 or 60 1 working liquid volume external-circulation-loop airlift (ECL-AL) fermentor, and in a geometrically similar 6 1 prototype, both equipped with perforated-plate spargers (1 mm dia. holes). Carboxymethylcellulose solutions were used to simulate the rheological behaviour non-Newtonian fermentation broths. The specific mixing time (θ/ V) is shown to be highly dependent on the dispersion height and gas superficial velocity in the riser section, as well as on the riser diameter and the effective viscosity of the liquid phase. In the range studied (0.111⩽ A D / A R ⩽0.46), the downcomer-to-riser cross-sectional-area ratio has a relatively minor effect on θ/ V. The superficial velocity of the circulating liquid in the riser ( u LR ) was also measured. The results have been combined with those of a previous investigation, by Popovic and Robinson, to better elucidiate the effect of dispersion height on the rate of liquid circulation. A modified correlation of u LR is presented and discussed.
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