A new drag model for CFD modeling of bubble columns with surfactant

Abstract

It is well known that a small amount of surfactant may significantly affect the flow stability in bubble columns, which cannot be interpreted by the slight variation of the liquid physical properties, e.g., surface tension, viscosity or density. The underlying mechanism is relevant to the interfacial dynamics due to surfactant concentration gradient. However, direct resolution of the micro-scale dynamics is challenging, as this requires complicated coupling of direct numerical simulation of interfacial dynamics and surfactant migration. In this study, a simplified correlative model was developed to take into account the surfactant effect on the average drag coefficient in the two-fluid model of CFD simulation. This novel drag model can improve the prediction of gas holdup in the homogeneous regime. By considering both the surfactant effect and swarm effect, the model can also reasonably estimate the gas holdup in the heterogeneous regime. A notable feature of this model is the reproduction of the peak of gas holdup at certain surfactant concentration in the experiments. Furthermore, although the model is based on the experimental data of ethanol solution, it can also predict the gas holdup in the bubble columns of other types of surfactants, e.g., butanol solution.