Heat and mass transfer enhancement in microchannels via flow instability induced by a composite structure of a flexible plate and a quarter-circular bluff body

To overcome the heat and mass transfer limitations of low Reynolds number microchannel flow, this paper proposes a flow instability-induced enhancement strategy by placing the flexible plate upstream of a bluff body to accelerate the local fluid flow. A quarter-circular bluff body is further selected to trigger an earlier vortex shedding due to the sharp-edge effect. The flow pattern transition is regulated by the composite structure. Its effects on heat and mass transfer performance including Nusselt number, outlet mixing efficiency and pressure loss are studied across various magnitudes of Reynolds number. The flow instability analysis reveals distinct flow regime transitions from laminar to vortex flow due to an increase in flexible plate height and Reynolds number. As compared to the isolated bluff body configuration, the introducing of the upstream flexible plate significantly reduces the critical Reynolds number for laminar-to-vortex flow transition by up to 67%. This induced flow instability substantially enhances the heat transfer and mixing performance. The composite structure achieves maximum Nusselt number improvements of 29%, 64%, and 49% and maximum mixing efficiency enhancements of 71%, 336%, and 32% at Reynolds numbers of 10, 30, and 90, respectively, as compared to the isolated quarter-circular configuration. The findings offer a promising strategy for improving the performance of microfluidic cooling systems and micromixers in low-Reynolds-number applications.