Numerical Analysis of Acoustophoretic Discrete Particle Focusing in Microchannels

Acoustophoretic particle focusing is a modern and very attractive method of removing a variety of objects from solutions in a microfluidic channel. The process is inherently general and can be readily extended to multiple types of applications such as healthcare (e.g. malignant cell removal), academic research (e.g. nanoparticle separation), industrial (e.g. reclaiming of rare earths) and environmental applications (e.g. sequestration of suspended solids). According to classical understanding, particle separation is realized by the acoustic radiation force. Traditionally, the wavelength of the acoustic wave has to be fine-tuned to the channel width and specified to λ = 2Lchannel. This creates a constant pressure node in the middle of the channel that forces particle motion towards it. Particle motion is theorized to be caused by differences in the pressure gradient acting on the partciles and/or wave scattering. This article also demonstrates that particle focusing can also be achieved under different conditions, provided that the amplitude of the oscillations is sufficiently high. In this study, results from numerical simulations performed in FLOW-3D help promote understanding of acoustophoretic particle focusing by closely examining the forces that act on the particles. To the best of our knowledge, this is the first explicit study of this phenomenon that focuses on the different force contributions This computational analysis can be generally applied to a multitude of acoustophoretic processes and should prove useful in promoting understanding of the phenomena involved in particle focusing.