CFD-PBM Modeling of Gas-Liquid Flow Through Screen-Type Static Mixers

Abstract

Gas-liquid flows are central to many chemical and environmental processes, where phase interactions govern bubble-size distribution, interfacial area, mass transfer, and overall reactor performance. Their significance is amplified in process intensification, where compact equipment is used to enhance transport rates while reducing operating volume and energy consumption. Screen-type static mixers are particularly relevant in this context, since they have been successfully applied to intensify gas-liquid operations such as oxygenation, ozonation, and carbon capture. However, the woven structure of screen mixers, together with their micro-scale openings, make fully resolved numerical simulations computationally expensive. This limitation motivates the use of a reduced geometric representation of these mixers that preserve the dominant hydrodynamic effects while remaining computationally manageable. In this work, a coupled computational fluid dynamics and population balance model (CFD-PBM) framework is developed and evaluated to predict the hydrodynamics and bubble-size evolution of gas-liquid flows through a reactor equipped with screen-type static mixers. Simulations are performed using a finite volume solver (ANSYS Fluent) using an Eulerian-Eulerian multiphase model. The dispersed gas phase is modeled using a class-based population balance approach, with bubble breakup and coalescence described via modified kernels from the literature. Mesh reliability is assessed through a grid convergence index analysis, and the model is validated against experimental measurements of pressure drop and mean bubble diameter. The results indicate that screens act as localized turbulence generators, concentrating energy dissipation over a short downstream distance and promoting bubble breakup in these regions. Farther downstream, as turbulence dissipation subsides, coalescence becomes the dominant mechanism. The coupled CFD-PBM model successfully reproduces this behavior, accurately predicting the axial evolution of bubble size along the reactor as well as the effect of solution contaminants on the dispersed phase behavior. Overall, the model reproduces the key physical mechanisms governing gas-liquid flow through screen-type static mixers. This thesis demonstrates that coupled CFD-PBM modeling provides a robust and physically consistent framework for analyzing turbulent gas-liquid dispersions in intensified systems such as screen-type static mixers. Moreover, the reduced-geometry approach is shown to deliver reliable predictions at a significantly lower computational cost compared to fully resolved simulations.