Oxygen transfer in three scales of concentric tube airlift bioreactors

Oxygen transfer was evaluated in three internal-loop airlift reactors (ALRs) of different working volumes (2, 5, and 10 dm3) and similar geometric configuration utilizing eight Newtonian and five non-Newtonian fluids. The effects of the superficial gas velocity (UGR) and liquid viscosity (μL) had opposite effects on the volumetric oxygen transfer coefficient (kLa). However, they presented the same orders of magnitude showing that the viscosity effect on oxygen mass transfer cannot be neglected. A correlation for kLa based on dimensional analysis considering the effects of the geometric parameters, the physical properties of the fluid, and the operational conditions presented a very good fitting to the experimental data. The correlation shows that the influence of the reactor internal diameter on kLa was considered positive. Therefore, in larger-scale reactors an appropriate oxygen transfer can be reached under smaller aeration conditions.