Fluid dynamics of a microfluidic micromixer–micropump driven by adjacent micro synthetic jets

Efficient mixing at the microscale remains a significant challenge in microfluidic systems due to the dominance of laminar flow and the consequent limitation of convective transport. Synthetic jets, generated by the oscillatory motion of a diaphragm within a cavity, produce a zero net mass flux while imparting periodic momentum to the surrounding fluid, thereby enabling localised flow perturbation and vortex generation that can substantially enhance mixing and mass transfer in microchannels. In this study, a pair of adjacent micro synthetic jets (AMSJs) is positioned perpendicularly to a microchannel to investigate their potential as a novel micropump-mixer. The vectoring effect of the adjacent jets, in which the phase difference between the actuators can manipulate the combined jet direction, is used to control internal flow structures. A numerical investigation examines the influence of four key parameters: the phase difference between actuators, the orifice-to-orifice centre separation distance, the Reynolds number of jets, and the stroke length with water as working fluid. The results show that reducing the orifice spacing strengthens jet interaction and suppresses secondary vortices. An optimal phase difference of approximately 130° produces a stable vectored jet. This configuration eliminates the need for external pumps or complex geometric features to induce cross-flow. In pumping mode, the AMSJ-driven device can sustain back pressures of up to 1.7kPa[jls-end-space/]and achieve flow rates of up to 23ml/min in a microchannel with a height of 200 μm[jls-end-space/], a length of 4.5mm[jls-end-space/], and a width of 1 mm. Strong vortex interaction, merging, and wall-induced secondary and tertiary vortices generate intense stretching and folding of the fluid interface, leading to rapid and efficient mixing of two miscible liquids. Mixing indices exceeding 0.9 are obtained within a few milliseconds for sufficiently large stroke lengths and moderate jet Reynolds numbers (Rej=100 and Lj=73[jls-end-space/]). These results demonstrate that AMSJs provide an effective, valveless, and compact approach for simultaneous pumping and mixing in microfluidic systems.