Chaotic mixing inside microdroplets in microchannel with slanted grooves and staggered-herringbone grooves

The present study employed simulation methods to investigate droplet-mixing-based chaos in microchannels with slanted grooves and staggered-herringbone grooves. The microdroplets rotate under the influence of transverse flow, generating two asymmetrical circulating vortices internally to enhance the mass transfer between the two halves of the droplet with mixed components. Compared to the slanted groove micromixer (SGM) with a 60° slanted angle, the SGM with a 45° slanted angle exhibited a more obvious difference in vortex size, resulting in higher mixing efficiency. The droplets rotate and stretch inside the staggered-herringbone groove micromixer (SHGM). Due to the influence of the interlaced structure, the internal vortex state exhibits continuous variation, thereby significantly enhancing the mixing efficiency. For SHGM, when the inlet velocities of the discrete phase and the continuous phase are 0.001 and 0.003 m/s, respectively, over 90% mixing efficiency is achieved after the droplet travels a distance of 0.6 mm, corresponding to an effective mixing time of 60 μs. Further studies were conducted on the effects of parameters such as two-phase flow velocity, surface tension, viscosity, contact angle on the thickness of the continuous liquid film, and the size of the corner flow, as well as on the variation pattern of the mixing efficiency of microdroplets. For SHGM, the time required to achieve complete mixing can be reduced to the order of tens of microseconds, with the ability to adjust the mixing time by modifying the control parameters.