LAUSR

Extensive experimental studies on internal-loop airlift reactors, including center-rising (CR-ALR) and annulus-rising airlift reactors (AR-ALR), have been reported in the literature. However, to the best of the authors' knowledge, the effects of the aeration mode on the local hydrodynamics remain an under-investigated area, especially for complex culture media. At present, it is difficult to select the best aeration mode for ALRs due to limited understanding of the pros and cons of the different modes. This study presents a detailed quantitative investigation of the overall gas holdup, local liquid velocity, liquid circulation time, shear rate distribution, and volumetric mass transfer coefficient in center- and annulus-rising airlift bioreactors to better understand the effect of aeration mode on airlift bioreactor performance. Particle image velocimetry is employed to conduct local measurements. The results show that the overall gas holdup, liquid circulation time, and volumetric mass transfer coefficient are larger in the AR-ALR than in the CR-ALR. The local liquid velocity circulating into the downcomer of the AR-ALR, which contributes to bubbles entrainment and therefore to overall gas holdup, is higher than in the CR-ALR. It was observed that a large circulation loop formed in the CR-ALR, whereas two counter-looping circulation cells appeared in the AR-ALR. It was also found that the shear rate field was more uniform in the AR-ALR than the CR-ALR although the shear rates were similar in magnitude. This article is protected by copyright. All rights reserved