Analysis of KLa Measurement Methods in Stirred Vessels: The Role of Experimental Techniques and Fluid Dynamic Models

Several dynamic and steady-state methods have been proposed in the literature for measuring the mass transfer coefficient in gas-liquid stirred vessels. Analysis has also been developed about the fundamentals of the most interesting techniques. Similarly, the flow behaviour of the gas and the liquid phases has been modelled in various ways – the different models often resulting in different KLa value estimates. Cross checking of a number of techniques and of various models has already been performed for a number of cases. However, not all the implications are clear and have been retained, especially for high-aspect-ratio equipment stirred with multiple impellers. In this paper the main problems in KLa characterisation are analysed: the most promising techniques and flow models are reviewed critically and several combinations of experimental methods and models have been tested with the purpose of providing information regarding their choice. Vessels stirred with sets of multiple impellers of different types as well as coalescing and non-coalescing gas-liquid systems have been considered. Recommendations about the use of some of the mentioned tools are also given, in relation to the final use of the coefficient.