Particle-train dynamics in curved microfluidic channels at intermediate Reynolds numbers

• Unusual particle-train dynamics were observed in curved microfluidic flows.
• Homogeneous particle-train twisting occurred in a transitional flow regime.
• Heterogeneously-sized particles self-organized at a transitional flow regime.
• Analysis explained particle focusing effects as a function of Reynolds number.
• Analysis explained heterogeneous particle-train organization.

A picture of the continuous transition of particle behavior with increasing Reynolds number (Re) is presented by the study of equilibrium positions andparticle array configurations in curved microfluidic channels. Particles with different diameters (d  =10–20μm) are studied flowing in curved channels of different heights (h  =50 and 100μm).The study focuses on an intermediate range (Re=10–40) where the competing inertial force and the Dean force result in complex phenomena which include particle train twisting, particle focusing in the same hybrid array, and the tendency of the smaller particles leading a hybrid array. These observations are coupled to numerical computations to further the quantitative understanding of the underlying physical systems. Three-dimensional finite-element modeling of the channel reveals the lateral flow-focusing position in the channel under varying Re. Dissipative hydrodynamic simulations describe the stability of each observed particle train configuration.