The mechanics of microparticle collection in an open fluid volume undergoing low frequency horizontal vibration

Manipulation of particles suspended in a fluid can be achieved using low frequency vibrations in an open fluid volume. The collection of particles at the solid-liquid (lower) interface is attributed to the generation of resonant capillary waves at the liquid-air (upper) interface. The resulting periodic flow field points to a hydrodynamic focusing mechanism which collects the particles over multiple cycles. This collection process is demonstrated by modelling the flow field produced in an open rectangular chamber undergoing horizontal oscillation. A particle tracing algorithm is then used to predict the collection locations of particles at different regions in the chamber. The modelling allows the collection mechanism to be understood and the effect of particle inertia on the process to be investigated; as a result, the speed of collection can be described as a function of particle size and density. The modelling results are supported by experimental observations in a rectangular well filled with water; the data show that particles with higher inertia collect faster. The effect of streaming is also observed in the experiments for particles with lower inertia.