Particle separation using modified Taylor’s flow

Abstract

In this study, the separation of micron-size particles from a liquid slug is achieved by using a passive mechanism through Taylor’s flow. We have exploited the recirculation of a fluid along the travelling air–liquid interfaces to align particles in a streamline. Recirculation of concentrated particles is achieved along the centre of the microchannel that aligns with the maximum velocity plane across the channel. The microchannel is fabricated through a four-step manufacturing process to achieve the necessary dimensions and surface chemistry along the side wall of the microchannel. For a flow of liquid, a fully developed flow regime can be witnessed by observing the parabolic velocity profile. The symmetric profile with maximum velocity along the center line of the channel is a depiction of the no-slip boundary at the channel wall. A liquid-repellent solid wall, or a superhydrophobic solid wall, changes the parabolic profile and subsequently, the magnitude and position of maximum velocity changes. Along a channel with one wall of superhydrophobic coating, the profile becomes asymmetric and the shifts location of the maximum velocity from the center of the channel. After introducing a bubble of the same size as the channel width, the bubble also experiences this asymmetry. As famously Taylor flow depicts, the traveling bubble concentrates the particles along a maximum velocity profile which is along the center of the channel towards the wall with slp condition. However, for one wall with slip condition, it facilitates the shift of the stream of particles on the desired side of the center of the channel. This shift is used to guide particles towards one arm of the Y section of the channel located downstream of the flow. To demonstrate this shift in the particle stream, we conducted experiments along two different channels: one with no slip condition, and the second with a coating that exhibits slip condition along the wall.