Passive mixing enhancement in microchannel flows using flexible structures

In the field of biomedical diagnostics and drug development-related chemical applications, miniaturised systems are employed and are usually termed microfluidic devices. Mixing samples and reagents in these devices must be mixed thoroughly before processing. The available mixing methods like active stirrers, high flow rate, additional pumping and active methods usually used in macro-scale devices cannot be used in microfluidic devices due to the dimensional constraints such as shorter channel length, and low Reynold number flows due to the viscosity-dominated biological flows. So, passive mixing processes are the best choice which solely rely on mass transport phenomena due to molecular diffusion, flow transition and chaotic advection. To assist these phenomena in micro-devices, usually, geometric designs are proposed and experimented which increase the contact surface area and decrease the diffusion path. Some such designs and passive mixing methods are T- and Y- Y-shaped mixers, separation and re-lamination mixers and serpentine-shaped mixers. In this work, we introduce structural flexibility in the channel geometrical design and investigate the flow agitation and its impact on the quality of the mixing process. We found that wall-mounted flexible structures inside a channel flow act as a passive stirrer that causes increased mixing efficacy than that in the case of rigid plates. We systematically investigate the various parametric influences on flow agitation, such as structure flexibility and inlet flow rate. This numerical setup involving flexible structures transforms a steady inlet flow into a periodic flow generator in the channel. This pumping effect, due to the 'passive stirrers' in the design, leads to flow transition and encourages fluid mixing. An efficient mixing device shall significantly advance the state-of-the-art developments in microfluidic devices. Also, similar inspirations can be forwarded to the mixing process across the scales in industries.