Ionic liquids show good prospect in gas-liquid reaction and separation processes. Investigation of flow and dispersion performance of gas/ionic liquid systems is important for the development of technology and devices for gas-liquid dispersion as well as application of ionic liquids in gas-liquid reaction and separation processes. The flow and dispersion performance of N2/[Bmim]BF4 in coaxial annular microchannels was investigated. Flow patterns of bubble-flow

bubble-slug-transition-flow

slug-flow and slug-annular-transition-flow were observed. The influence of gas and liquid flow rates on gas-liquid flow pattern was studied in different microchannels and flow pattern maps were determined accordingly. The effects of gas and liquid flow rates on dispersion size were also investigated. The mechanism was discussed and mathematical models were established to predict the dispersion size in different microchannels.