Curved microchannels take advantage of inertial and Dean drag forces to achieve size-based separation of particles and cells. Despite the reported numerical and experimental correlations for Dean velocity (VDe) of Newtonian fluids, comprehensive studies and correlations are still required for the flow of viscoelastic fluids in curved microchannels. In this paper, the effects of curved channel height, radius of curvature, and kinematic viscosity were investigated to derive an empirical correlation for VDe of viscoelastic water. The developed knowledge of viscoelastic Dean flow velocity will be vital in design of elasto-inertial microfluidic devices for determination of lateral displacement of fluids in fluid exchange and Dean drag force in particle focusing and separation applications.

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We report the effects of a curvilinear microchannel width, height, and radius of curvature, as well as the kinematic viscosity and axial velocity of shear-thickening nanofluids, on the average Dean velocity ( VDe) of the secondary flow in the microchannel. Manipulation of inertial and Dean drag forces in curvilinear microchannels has enabled high throughput and high-resolution size-based separation of microparticles and cells in various biomedical applications. VDe plays a deterministic role in the estimation of the Dean drag force and the design of these microfluidic devices. In spite of the previous numerical and experimental studies on VDe of Newtonian and shear-thinning viscoelastic fluids, VDe of shear-thickening metallic nanofluids, such as SiO2 nanoparticles in water, in curved microchannels is still unknown. Such shear-thickening fluids are being used in thermal microsystem applications and are on the verge of entering the field of inertial microfluidics for particle and cell sorting. Our investigations have shown that VDe of shear-thickening SiO2-water nanofluids scales directly with the channel width and the fluid axial velocity, while being inversely proportional with the SiO2 concentration and the channel radius of curvature. Our non-dimensional analysis has led to the development of an empirical correlation that relates VDe-based Reynolds number of the nanofluid to the Dean number and the normalized kinematic viscosity of the nanofluid. It provides a significant accuracy in estimating VDe of shear-thickening fluids, compared to application of Newtonian or shear-thinning equations in the literature, which could be useful towards future design of particle and cell sorting and washing microdevices.

Separation and solution exchange of microparticles in non-Newtonian fluids are vital steps in biomedical applications. Dean drag and elastic forces in curved (and straight) microchannels lead to microparticle focusing in...

This paper describes a method for the synthesis of silica nanoparticles that can be later used for coating of quantum dots inside a microfluidic reactor. Here, a droplet-based system is used where two reagents were mixed inside the droplets to obtain silica. Particles in the size range of 25±2.7 nm were obtained with comparable size distribution to controlled batchwise synthesis methods. This method is suitable to be used later to coat CdSe nanoparticles inside the microreactor.