A micromixer with consistent mixing performance for a wide range of flow rates

Characterization of the oil water two phase flow in a novel microchannel contactor equipped with helical wire static mixer

This study investigates an oil/water two-phase system to assess the potential efficacy of a novel passive mixer in enhancing the liquid-liquid interfacial area within a micro-channel contactor. In this system, two fluids are introduced into a microchannel with a diameter of 800 μm and a length of 20 cm, which is equipped with a stainless-steel helical wire measuring 250 μm in diameter. Throughout the experiments, both fluids are supplied at equal flow rates, and the dominant forces, including attachment and detachment forces, are examined. The results reveal a critical Weber number of 3.8 × 10-³, at which the first detachment occurs. A comparison between microchannels with and without the passive micromixer demonstrates that greater slug breakup occurs in the system incorporating the helical wire micromixer. This innovative configuration results in a significant reduction in slug/droplet size compared to a microchannel without a barrier, decreasing from approximately 600 μm to 390 μm at a flow rate of 0.8 mL/min. Additionally, a flow map is presented, illustrating three distinct flow regimes: flow contains long slug, Slug-droplet flow, and droplet flow regimes, with the droplet flow regime covering the largest area. The findings indicate that the implementation of this innovative passive mixer substantially increases the interfacial area, providing significant advantages for mass transfer applications.

An acoustofluidic device for efficient mixing over a wide range of flow rates

Whether reagents and samples need to be combined to achieve a desired reaction, or precise concentrations of solutions need to be mixed and delivered downstream, thorough mixing remains a critical step in many microfluidics-based biological and chemical assays and analyses. To achieve complete mixing of fluids in microfluidic devices, researchers have utilized novel channel designs or active intervention to facilitate mass transport and exchange of fluids. However, many of these solutions have a major limitation: their design inherently limits their operational throughput; that is, different designs work at specific flow rates, whether that be low or high ranges, but have difficulties outside of their tailored design regimes. In this work, we present an acoustofluidic mixer that is capable of achieving efficient, thorough mixing across a broad range of flow rates (20-2000 μL min-1) using a single device. Our mixer combines active acoustofluidic mixing, which is responsible for mixing fluids at lower flow rates, with passive hydrodynamic mixing, which accounts for mixing fluids at higher flow rates. The mechanism, functionality, and performance of our acoustofluidic device are both numerically and experimentally validated. Additionally, the real-world potential of our device is demonstrated by synthesizing polymeric nanoparticles with comparable sizes over a two-order-of-magnitude wide range of flow rates. This device can be valuable in many biochemical, biological, and biomedical applications. For example, using our platform, one may synthesize nanoparticles/nanomaterials at lower flow rates to first identify optimal synthesis conditions without having to waste significant amounts of reagents, and then increase the flow rate to perform high-throughput synthesis using the optimal conditions, all using the same single device and maintaining performance.