Abstract
Suitable methods to realize a multi-dimensional fractionation of microparticles smaller than {10},upmu mathrm{{m}} diameter are still rare. In the present study, size and density fractionation is investigated for 3.55,upmu mathrm{{m}} and {9.87},upmu mathrm{{m}} particles in a sharp-corner serpentine microchannel of cross-sectional aspect ratio h/w = 0.25. Experimental results are obtained through Astigmatism Particle Tracking Velocimetry (APTV) measurements, from which three-dimensional particle distributions are reconstructed for Reynolds numbers between 100 and 150. The 3D reconstruction shows for the first time that equilibrium trajectories do not only develop over the channel width, i.e. in-plane equilibrium positions but also over the channel height at different out-of-plane positions. With increasing Reynolds number, 9.87,upmu mathrm{{m}} polystyrene left( rho _{mathrm{{PS}}} = 1.05,mathrm{{g}};mathrm{{cm}}^{-3} right) and melamine left( rho _mathrm{{MF}} = 1.51,mathrm{{g}};mathrm{{cm}}^{-3} right) particles focus on two trajectories near the channel bisector. In contrast to this, it is shown that 3.55,upmu mathrm{{m}} polystyrene particles develop four equilibrium trajectories at different in-plane and out-of-plane positions up to a critical Reynolds number. Beyond this critical Reynolds number, also these particles merge to two trajectories at different channel heights. While the rearrangement of 3.55,upmu mathrm{{m}} polystyrene particles just starts beyond mathrm{{Re}}>140, 9.87,upmu mathrm{{m}} polystyrene particles undergo this rearrangement already at Re=100. As the equilibrium trajectories of these two particle groups are located at similar out-of-plane positions, outlet geometries that aim to separate particles along the channel width turn out to be a good choice for size fractionation. Indeed, polystyrene particles of different size assume laterally well-separated equilibrium trajectories such that a size fractionation of nearly 100% at Re=110 can be achieved.
Highlights
Microparticles with diameters below 10 μm and well-defined properties are increasingly used in e.g. the pharmaceutical and chemical industry or metallurgy (Baghban Taraghdari et al 2019; Li et al 2019; Kumar and Venkatesh 2019)
To validate the capability of the serpentine microchannel to fractionate particles according to size and density, three-dimensional particle distributions are determined in a first step
The size and density fractionation performance of a sharp corner serpentine channel was investigated for defined particle combinations
Summary
Microparticles with diameters below 10 μm and well-defined properties are increasingly used in e.g. the pharmaceutical and chemical industry or metallurgy (Baghban Taraghdari et al 2019; Li et al 2019; Kumar and Venkatesh 2019). Multi-dimensional fractionation processes are essential to fabricate intermediate particle products with e.g. monodisperse size, shape or surface properties. Microfluidic particle fractionation has been realized by means of active as well as passive approaches. While active approaches utilize external acoustic, magnetic or electrical force fields (Nilsson et al 2004; Suwa and Watarai 2011; Podoynitsyn et al 2019), passive approaches only rely on hydrodynamic forces. Inertial effects may be utilized to force particles on certain equilibrium trajectories, whose position depends on both the particle and fluid flow properties. Inertial effects include particle centrifugal forces, as well as inertial particle migration, which is present if the particle diameter is large compared to the channel dimensions (Di Carlo 2009).
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