Gas-liquid-liquid multiphase flow in microfluidic systems – A review

Gas-liquid-liquid (G/L/L) multiphase flow in microfluidic system has been a vital part of microfluidics, micro-chemical and micro-analysis in recent years. Microfluidics has emerged as a useful tool to prepare G/L/L that affords improved control over the micro-scale structure. With the aid of clever and efficient device designs, precise regulation of the size, shape and components can be realized. Existing results have shown that G/L/L multiphase micro-flow exhibits more complicated laws and unique characteristics in flow, transport and reactions compared with liquid-liquid or gas-liquid two-phase flow, allowing the optimal and more efficient control of the process. In this review, focused on the G/L/L multiphase flow in microfluidic systems, we recount the historical development of this system and approach, along with the state-of-the-art, including discussion of microfluidic devices (lithographically defined devices and capillary/needle-based devices) and microchannel type (cross-junction, flow-focusing, dual-coaxial, etc.) used to form and prepare G/L/L multiphase mixtures. Discussion is also extended to scaling laws and numerical simulations used to predict the size of microbubbles or droplets. In addition, flow and mass transfer characteristics, as well as applications and scale-up, are also discussed. Finally, the future trends in the development of G/L/L multiphase flow are addressed, emphasizing some directions worth detailed study and remaining challenges in the field.