New criteria for application of the well-mixed model to gas-liquid mass transfer studies

The well-mixed model presents several advantages for the evaluation of interphase mass transfer rates in gas-liquid contactors: it simplifies the mathematical analysis and eliminates the need for measuring numerous mixing parameters. Although the well-mixed model corresponds to a theoretical concept, it is shown in this paper that, under certain conditions, it can be safely applied to the liquid phase of contactors for the purpose of determining the overall volumetric mass transfer coefficient KLaL. Based on a computer simulation of absorption and mixing processes, simple criteria were developed that specify the conditions for which the well-mixed model is applicable in practice, for either a semi-batch gas-liquid contactor or a continuous flow absorber at steady-state. The dimensionless group KLaLτc, where τc is the average circulation time in the liquid phase of the contactor, was found to be a key parameter in establishing the validity of the well-mixed model.