Deformable baffles coupled with pulsatile flow improve mixing in microfluidic devices

An important objective for many microfluidic mixer devices is to attain a high level of mixing efficiency at low Reynolds numbers. Previous research incorporating rigid obstacles into microchannels has shown enhanced chaotic advection and improved mixing index; however, the increased pressure drop and corresponding shear forces within the fluid domain can create issues in biological applications. In this paper, we show how an innovative micromixer strategy, i.e., incorporating deformable baffles and utilizing pulsatile flow, results in a high level of mixing efficiency at low Reynolds numbers (Re =1.25), where diffusion is the pure mechanism of mixing. The numerical investigation involved solving the continuity, Navier-Stokes, solid mechanics, and fluidsolid interaction equations alongside a convection-diffusion model to analyze species concentration. To find the best conditions of the micromixer, the mixing index as the objective function was optimized, and various parameters, including phase difference, velocity ratio, Strouhal number, baffle distance, and Reynolds number, were investigated. Through optimization of these parameters, we show a notable improvement in the mixing index (increase from 21.7 % to 78.86 %) at a Reynolds number of 1.25 with 2 mixing units, more than 92 % mixing efficiency by using 6 mixing units, and more than 95 % mixing efficiency at a Reynolds number of 0.1. Moreover, the incorporation of deformable baffles and pulsation results in a lower pressure drop. These conditions are optimal for biological applications that require thorough mixing of the sample inputs.