Simplified dynamic pressure method for kLa measurement in aerated bioreactors

Abstract

A simplified version of the dynamic pressure method for measuring mass-transfer coefficients in gas–liquid systems is proposed. With this method oxygen concentration in the liquid phase is monitored after a sudden change of total pressure is applied to the system. With respect to the original technique introduced by Linek [14] the simplified version here proposed greatly simplifies the data treatment, yet resulting in good accuracy for most practical purposes. In practice, with the help of a simple mathematical model, it is found that the dynamic oxygen concentration response, when plotted as residual driving force versus time in a semi-log diagram, should be expected to finally settle on a straight line. From the slope of this last kLa can be immediately computed. Experimental data obtained on a lab-size stirred tank reactor confirm all model predictions, including the feature that the adoption of large pressure changes may lead to better accuracy. Mass transfer coefficient data obtained by means of the simplified dynamic pressure method (SDPM) here proposed are compared with the relevant data obtained on the same system by the most accurate physical technique (pure oxygen absorption in a pre-evacuated liquid), as well as with the literature data, resulting in SDPM full validation. All kLa data obtained are finally organized by a conventional power law correlation.