Electroosmotic flow mixing in zigzag microchannels

Abstract

In this study we performed numerical and experimental investigations into the mixing of EOFs in zigzag microchannels with two different corner geometries, namely sharp corners and flat corners. In the zigzag microchannel with sharp corners, the flow travels more rapidly near the inner wall of the corner than near the outer wall as a result of the higher electric potential drop. The resulting velocity gradient induces a racetrack effect, which enhances diffusion within the fluid and hence improves the mixing performance. The simulation results reveal that the mixing index is approximately 88.83%. However, the sharp-corner geometry causes residual liquid or bubbles to become trapped in the channel at the point where the flow is almost stationary, when the channel is in the process of cleaning. Accordingly, a zigzag microchannel with flat-corner geometry is developed. The flat-corner geometry forms a convergent-divergent type nozzle which not only enhances the mixing performance in the channel, but also prevents the accumulation of residual liquid or bubbles. Scaling analysis reveals that this corner geometry leads to an effective increase in the mixing length. The experimental results reveal that the mixing index is increased to 94.30% in the flat-corner zigzag channel. Hence, the results demonstrate that the mixing index of the flat-corner zigzag channel is better than that of the conventional sharp-corner microchannel. Finally, the results of Taguchi analysis indicate that the attainable mixing index is determined primarily by the number of corners in the microchannel and by the flow passing height at each corner.

Vortex generation in electroosmotic flow passing through sharp corners

“…The experimental images were captured by an optical microscope (Model: Eclipse 50i, Nikon, Japan), filtered spectrally, and then observed using a charge-coupled device camera (CCD, model: SSC-DC50A, Sony, Japan). The mixing effectiveness within the microchannel was quantified based on the intensity of the Rhodamine B sample using the mixing index presented in Lin et al (2005) and Chen and Yang (2007), i.e.…”

Enhancement of electrokinetically driven microfluidic T‐mixer using frequency modulated electric field and channel geometry effects

“…A droplet-based microfluidic system was also reported to achieve fast mixing by inducing chaotic flow inside droplets moving through winding microchannels [10]. In addition, Chen and Yang [11] investigated electrokinetic mixing in zigzag microchannels with sharp and flat corner geometries, and found that the electrokinetic mixing index of the flat-corner zigzag channel is better than that of the conventional sharp-corner microchannel. Active mixers utilize external driving forces to disturb the flow and thus to enhance mixing.…”

Millisecond-order rapid micromixing with non-equilibrium electrokinetic phenomena

“…This type of mixer typically relies on complex flow patterns, which define unique structures of different passive mixers. Various passive micromixers have been reported: branched-microchannels (Erbacher et al 1999), staggered herringbone mixers (Stroock et al 2002;Villermaux et al 2008), zigzag-shaped channels (Chen and Yang 2007;Egawa et al 2009), three-dimensional nanopore structures (Park et al 2009), and split-and-recombine configurations (Hardt et al 2005(Hardt et al , 2006Tofteberg et al 2010). Active mixers, on the other hand, operate with external energy input and thus mixing is achieved with various external disturbances.…”