Bubble formation dynamics in various flow-focusing microdevices.

The aim of this study is to investigate three types of gas-liquid micromixer geometries, including a cross-shape and two converging shape channels for the bubble formation in different liquids. The bubble shape, size, and formation mechanism were investigated under various experimental conditions such as the flow rates of two phases, physical properties of the liquid, and mixer geometries. A micro particle image velocimetry technique and a high-speed camera were used to characterize and quantify gas-liquid flows. It was revealed that the bubble formation, in particular the bubble size, depends on the geometry of the mixing section between two phases. A correlation gathering numerous experimental data was elaborated for the estimation of the bubble size. The influence of different parameters such as the flow rate ratio between two phases, surface tension, and liquid viscosity is well taken into consideration on the basis of the understanding of the bubble formation mechanism at the microscale. This paper marks an original improvement in the domain where no flow field characterizations or correlations were established in flow-focusing devices.