Application of electrokinetic instability flow for enhanced micromixing in cross-shaped microchannel

Huang, Minzhong; Yang, Ruey-Jen; Tai, Chang-Hsien; Tsai, Chien‐Hsiung; Fu, Lung-Ming

doi:10.1007/s10544-006-0034-z

Cited by 65 publications

(33 citation statements)

References 43 publications

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“…The absolute instability always occurs at a high intensity of the electric field. Recently, this instability flow has also direct applications to rapid electrokinetic passive mixing in a DC field (Park et al 2005;Tai et al 2006;Huang et al 2006). However, there are two disadvantages of the application of electrokinetic instability flow to microfluidic mixing.…”

Section: Electrokinetic Instability (Eki) Mixingmentioning

confidence: 99%

Electrokinetic mixing in microfluidic systems

Chang

Yang

2007

Microfluid Nanofluid

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The applications of electrokinetics in the development of microfluidic devices have been widely attractive in the past decade. Electrokinetic devices generally require no external mechanical moving parts and can be made portable by replacing the power supply by small battery. Therefore, electrokinetic-based microfluidic systems can serve as a viable tool in creating a lab-on-a-chip (LOC) or micro-total analysis system (TAS) for use in biological and chemical assays. Mixing of analytes and reagents is a critical step in realizing lab-on-a-chip. This step is difficult due to the flow in microscale devices which are typically limited to low Reynolds numbers, turbulence does not readily occur. The mixing of two or more fluid streams in a simple microchannel is dominated by the molecular diffusion effect. The diffusive mixing time is given by t m ~ w 2 /D and the mixing length (l m ) along the downstream channel increases linearly with the Péclet number (i.e. l m ~ Pe×w), where w and D are the channel width and molecular diffusivity. However, the rate of diffusive mixing in microscale channels is very slow compared to the convection of the fluid along the channel since the Péclet number of typical microchannel flows is very high due to biomolecules (e.g. DNA and protein) with relatively low molecular diffusivities. To reduce the mixing time and length, various schemes to enhance micro-mixing have been proposed in the past years. This review reports recent developments in the micro-mixing schemes based on DC and AC electrokinetics. The overview given in this article provides a potential user or researcher of electrokinetic-based technology to select the most favorable mixing scheme for applications in the field of micro-total analysis systems. Mixing principle and chaotic mixingAlthough it is difficult to induce turbulence (so-called Eulerian chaos) in microchannels, an effective mixing in low Reynolds number flow regimes can be obtained by the chaotic advection mechanism (or so-called Lagrangian chaos or laminar chaos), which provides an effective increase in the interfacial contact area and concentration gradient due to reduction of the striation thickness (i.e. diffusion length).In this way, mixing time and length can be considerably reduced. If an exponential reduction of striation thickness should occur, the mixing time and mixing length can be reduced down to t m ~ ln(Pe) and l m ~ ln(Pe), respectively, for chaotic flows in the limit of large Pe. An effective mixing always requires repeated stretching and folding of fluid elements, e.g blanking vortex models. Blinking vortex models are similar to the link twist map (LTM) strategy which is based on a dynamic system theory described in the literature [1]. An LTM is often obtained when the dynamic system has a structure such that the motion can be described by the repeated application of two twist maps. Over the past few years, many effective micromixers have been designed according to the LTM strategy. Micro-mixing based on electrokinetics

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Section: Electrokinetic Instability (Eki) Mixingmentioning

confidence: 99%

Electrokinetic mixing in microfluidic systems

Chang

Yang

2007

Microfluid Nanofluid

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272

150

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“…8 According to a recent review, Chang and Yang 9 implied that, so far, many efforts have been made to enhance mixing in microfluidics, e.g. using sufficiently high DC or AC voltage to force flow in a microchannel based on electrokinetic instability, [10][11][12][13][14][15] but the forced flows in these studies are chaotic advection, not turbulence. Can there be turbulence in a microchannel with Re on the order of 1?…”

Section: Introductionmentioning

confidence: 99%

There can be turbulence in microfluidics at low Reynolds number

2014

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Turbulence is commonly viewed as a type of macroflow, where the Reynolds number (Re) has to be sufficiently high. In microfluidics, when Re is below or on the order of 1 and fast mixing is required, so far only chaotic flow has been reported to enhance mixing based on previous publications since turbulence is believed not to be possible to generate in such a low Re microflow. There is even a lack of velocimeter that can measure turbulence in microchannels. In this work, we report a direct observation of the existence of turbulence in microfluidics with Re on the order of 1 in a pressure driven flow under electrokinetic forcing using a novel velocimeter having ultrahigh spatiotemporal resolution. The work could provide a new method to control flow and transport phenomena in lab-on-a-chip and a new perspective on turbulence.

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“…The use of electrokinetic instability (EKI) as a mixing technique for electrokinetically driven microfluidic flows with conductivity gradients has received considerable attention in recent years [36][37][38][39][40]. In an attempt to improve the mixing performance of micromixers, Tai et al [39] developed a T-type mixer with parallelogram barriers within the microchannels.…”

Section: Introductionmentioning

confidence: 99%

Numerical analysis of a rapid magnetic microfluidic mixer

et al. 2011

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This paper presents a detailed numerical investigation of the novel active microfluidic mixer proposed by Wen et al. (Electrophoresis 2009, 30, 4179-4186). This mixer uses an electromagnet driven by DC or AC power to induce transient interactive flows between a water-based ferrofluid and DI water. Experimental results clearly demonstrate the mixing mechanism. In the presence of the electromagnet's magnetic field, the magnetic nanoparticles create a body force vector that acts on the mixed fluid. Numerical simulations show that this magnetic body force causes the ferrofluid to expand significantly and uniformly toward miscible water. The magnetic force also produces many extremely fine finger structures along the direction of local magnetic field lines at the interface in both upstream and downstream regions of the microchannel when the external steady magnetic strength (DC power actuation) exceeds 30 Oe (critical magnetic Peclet number Pe(m),cr = 2870). This study is the first to analyze these pronounced finger patterns numerically, and the results are in good agreement with the experimental visualization of Wen et al. (Electrophoresis 2009, 30, 4179-4186). The large interfacial area that accompanies these fine finger structures and the dominant diffusion effects occurring around the circumferential regions of fingers significantly enhance the mixing performance. The mixing ratio can be as high as 95% within 2.0 s. at a distance of 3.0 mm from the mixing channel inlet when the applied peak magnetic field supplied by the DC power source exceeds 60 Oe. This study also presents a sample implementation of AC power actuation in a numerical simulation, an experimental benchmark, and a simulation of DC power actuation with the same peak magnetic strength. The simulated flow structures of the AC power actuation agree well with the experimental visualization, and are similar to those produced by DC power. The AC and DC power actuated flow fields exhibited no significant differences. This numerical study suggests approaches to maximize the performance of the proposed rapid magnetic microfluidic mixer, and confirms its exciting potential for use in lab-on-a-chip systems.

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Application of electrokinetic instability flow for enhanced micromixing in cross-shaped microchannel

Cited by 65 publications

References 43 publications

Electrokinetic mixing in microfluidic systems

Electrokinetic mixing in microfluidic systems

There can be turbulence in microfluidics at low Reynolds number

Numerical analysis of a rapid magnetic microfluidic mixer

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