A Review on the Hydrodynamics of the Liquid-Liquid Two-Phase Flow in the Microchannels

The ability of small and microchannels to enhance mass transfer, reduce diffusional limitations, and create a safer process has made them the best choice for process intensification. This study provides a review of the available experimental and computational literature on the hydrodynamics of liquid-liquid two-phase flow in microscale, namely, flow regimes, pressure drop, and flow structure. When two immiscible liquids flow in small channels, various flow patterns can be observed, with the development of those patterns being influenced by several parameters, such as the geometry of the mixing junction and channel, the channel material, the fluids properties, and the orientation of the flow. As part of the flow patterns observations and measurement, the velocity fields and internal circulation reported in the literature were reviewed in the context of the microparticle velocimetry (μPIV) implementation. Also, relevant to our study is the literature outlining, pressure drop, and the available models that have been used to predict it. These models are discussed in detail with special reference to flow patterns and fluids viscosities. Moreover, the numerical studies results using computational fluid dynamics (CFD) have also been reviewed and discussed, in terms of the validity of the simulation and the different parameters affecting slug formation and flow patterns. Each section of the discussion also points out the gaps in the research and proposes future work that could further develop the technology under a review of liquid-liquid two-phase flow in microchannels.