A comprehensive review of gas-liquid two-phase flow in static mixers

In this study, the gas-liquid two-phase flow in the static mixer is comprehensively reviewed from the macroscopic hydrodynamic characteristics to the mesoscopic bubble dynamic behaviors. Firstly, the classification of static mixers and their applications in gas-liquid two-phase flow are summarized. Secondly, the research on energy efficiency and bubble characteristics in the static mixer is outlined. The experimental techniques for measuring the pressure drop (gyp) and identifying bubbles are mainly introduced and the evaluation parameters of flow and mixing characteristics are analyzed, which includes gyp, Sauter mean diameter (d32) and volumetric mass transfer coefficient (kLa). The non-swirling and swirling flow patterns are systematically analyzed and the evolution characteristics of gas-liquid two-phase flow are discussed in horizontal and vertical static mixers. In addition, the multi-scale modeling method of coupling computational fluid dynamics (CFD) and population balance model (PBM) is summarized and the important theories of bubble dynamics are elucidated, which encompass bubble drag, coalescence and breakup models. The applicability and limitations of different models in predicting the bubble size are analyzed. Finally, the flow mechanism of gas-liquid systems in static mixers is systematically summarized and its future prospects are presented.