Experimental analysis of flow topology and particle behavior in microcavities

Abstract

Efficient hydrodynamic particle trapping requires the precise control of flow structures that serve as hydrodynamic traps. Microfluidic structures, such as microcavities of various shapes and sizes, can be applied as hydrodynamic traps, and the exerting force can be controlled by changing the geometrical parameters and flow regimes of the cavities. In this study, the capability of trapping microparticles in rectangular, semicircular, and triangular microcavities is experimentally investigated. The flow structure in microcavities with a length-to-depth ratio L/h of 1–4 for rectangular cavities and L/h = 1–2 for semicircular and triangular cavities at a Reynolds number ranging between 1 and 1000 is visualized using a microparticle image velocimetry system. Additionally, patches of 20 µm particles are visualized using a high-speed camera. Different flow phases, namely attached, transitional, and separated, are observed and correlated with the cavity parameters and flow regime. Additionally, qualitative flow parameters determining particle behavior, such as the vortex center location and temporal vortical stability, are analyzed. Finally, the particle behavior is correlated with the flow structure in the cavities, and guidelines for the development of the optimal design of micro- and nanofluidic devices are discussed.