Experimental investigation of microparticle focusing in SiO2 nanofluids inside curvilinear microchannels

Curvilinear microchannels have enabled high throughput sized-based separation and manipulation of microparticles. Real life applications usually deal with fluid’s non-Newtonian behavior, where particles dynamics are altered compared to Newtonian mediums. Despite multiple reports on particle manipulation in shear-thinning fluids, no fundamental experimental investigation has been reported on microparticle focusing behavior inside shear-thickening fluids such as metallic oxide nanofluids in water (e.g., SiO₂-water). These nanofluids pose unique thermal characteristics and exhibit a drastic increase in viscosity as the shear rate rises in the microchannel. Here, we investigate the particle focusing behavior of co-flows of SiO₂ nanofluids inside curved microchannels with various channel widths and radii of curvature. We also report on the effect of nanofluid concentration, fluid axial velocity, and the particle size on particle migration. We observed a behavioral change in particle migration in SiO₂ nanofluids, where the shear-dependent effect could enhance the particle focusing at lower flow rates. Moreover, the dominance of Dean drag at higher axial velocities would dominate the particle migration and transfer them towards two focusing peaks close to the sidewalls. A thorough investigation of particle behavior in nanofluids inside curved microchannels could enable future applications in heat exchangers, solar energy collectors, and nanoplastic detection.