Effects of geometrical confinement on the generation of droplets at microfluidics T-junctions with rectangle channels

Abstract

Despite the fact that there are not a few relative studies, the effects of geometrical confinement on droplets’ generation at micro-T-junctions are not explicitly addressed. A three-dimensional volume of fluid (VOF) CFD model is developed here to study this classic microfluidics problem. The micro-T-junctions are designed with arms of a same hydraulic diameter but different width-to-depth ratios (\(\chi \) = 1/10–10), covering both deep-style (\(\chi <1)\) and flat-style T-junctions (\(\chi >1)\). It is found that the width-to-depth ratio (confinement style) shows complex effects on the dynamics of droplets’ generation. At \(\chi \le 1/10\), droplets are failed to be generated at the T-junctions. Compared to the normal T-junctions (\(\chi >1\)), the deep-style T-junctions (\(1/6<\chi <\) 1) show much higher generation frequency of droplets at \({\mathrm{Ca}}_{\mathrm{c}}>0.06\) and the volume of generated droplets scales with \({{\mathrm{Ca}}_{\mathrm{c}}}^{-1}\) instead of typical \({{\mathrm{Ca}}_{\mathrm{c}}}^{-0.33}\). The comparative study of two paired T-junctions with reciprocal width-to-depth ratio (e.g., a deep-style T-junction, \(\chi \) = 1/3 and a flat-style T-junction, \(\chi \) = 3) explicitly illustrates that the geometrical confinement stabilizes the generation dynamics of droplets at T-junctions. The mechanism for the stabilization effect is discussed. It provides some new insights in terms of designing devices of droplets’ generation.