Prediction of mean bubble size in pneumatic reactors

In the present work, a new methodology to estimate the mean bubble size (dB) in pneumatic bioreactors is proposed. The semi-theoretical method is based on Higbie's penetration theory and estimates dB. It uses experimental gas hold-up (ɛ) data and volumetric mass transfer coefficient (kLa) obtained in three scales of concentric-tube airlift reactor (ALR) of 2, 5 and 10 dm3 and three different pneumatic bioreactors of 2 dm3, which are concentric-tube airlift reactor (ALR), bubble column reactor (BCR) and split airlift reactor (SAR). The parameter kLa was separated into its components kL and a. Mean bubble size (dB) and convective oxygen transfer coefficient (kL) proved not dependent on the superficial gas velocity in the riser (UGR) for ALR and SAR and superficial gas velocity (UG) for BCR reactor in the experimental range studied. The results indicate that kLa is a function only of the gas–liquid interfacial area of the bubbles (a) and therefore of the gas hold-up (ɛ).