Electrohydrodynamic mixing and instability induced by co-linear fields and conductivity gradients

Hoburg, James F.; Melcher, James R.

doi:10.1063/1.861967

Cited by 57 publications

(39 citation statements)

References 5 publications

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“…An important comparison to this work is the temporal stability analysis of an electrohydrodynamic instability with zero base flow (Hoburg & Melcher 1976, 1977. The mechanism proposed by Hoburg & Melcher is qualitatively similar to that described in figure 17.…”

Section: Mechanism Of Electrokinetic Instabilitymentioning

confidence: 66%

Convective and absolute electrokinetic instability with conductivity gradients

et al. 2005

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Electrokinetic flow instabilities occur under high electric fields in the presence of electrical conductivity gradients. Such instabilities are a key factor limiting the robust performance of complex electrokinetic bio-analytical systems, but can also be exploited for rapid mixing and flow control for microscale devices. This paper reports a representative flow instability phenomenon studied using a microfluidic T-junction with a cross-section of 11 µm by 155 µm. In this system, aqueous electrolytes of 10:1 conductivity ratio were electrokinetically driven into a common mixing channel by a steady electric field. Convectively unstable waves were observed with a nominal threshold field of 0.5 kV cm −1 , and upstream propagating waves were observed at 1.5 kV cm −1 . A physical model has been developed for this instability which captures the coupling between electric and flow fields. A linear stability analysis was performed on the governing equations in the thin-layer limit, and Briggs-Bers criteria were applied to select physically unstable modes and determine the nature of instability. The model predicts both qualitative trends and quantitative features that agree very well with experimental data, and shows that conductivity gradients and their associated bulk charge accumulation are crucial for such instabilities. Comparison between theory and experiments suggests the convective role of electro-osmotic flow. Scaling analysis and numerical results show that the instability is governed by two key controlling parameters: the ratio of dynamic to dissipative forces which governs the onset of instability, and the ratio of electroviscous to electro-osmotic velocities which governs the convective versus absolute nature of instability.

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Section: Mechanism Of Electrokinetic Instabilitymentioning

confidence: 66%

Convective and absolute electrokinetic instability with conductivity gradients

et al. 2005

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“…Although the instability mechanism was not fully understood, a more systematic investigation by Chen and Santiago (2002) established the critical importance of conductivity gradient and high electric field strength in inducing the instability. Further studies by Santiago and co-authors (Chen et al, 2005;Lin et al, 2004) related the instability physics with earlier works on electrohydrodynamic (EHD) instability by Hoburg and Melcher (1976), Hoburg and Melcher (1977) and Baygents and Baldessari (1998). Combining linear analysis and nonlinear numerical simulations, these studies provided a comprehensive model framework for the understanding and prediction of EKI, and the results compared favorably with experimental measurements.…”

Section: Introductionmentioning

confidence: 87%

Electrokinetic instability in microchannel flows: A review

Lin

2009

Mechanics Research Communications

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“…Alternatively, active mixers have been reported using temporally controlled flow profiles with sequential flow switching between two inlets [14], by superimposing low frequency sinusoidally fluctuating flow on a steady state flow [15] and using magnetic microstirrers [16]. A category of active mixing techniques has also been reported using conductivity gradients first in macroscale systems [17,18] and more recently on the microscale using conductivity gradients that are perpendicular to the flow direction [19][20][21] and electrokinetically driven mixing [22] where an AC electric field is used to produce a flow instability that mixes the two phases. The use of electrohydrodynamic (EHD) instability for mixing between a single phase with spatially varying conductivity has also been reported [23,24].…”

Section: Introductionmentioning

confidence: 99%

Two phase micromixing and analysis using electrohydrodynamic instabilities

Zahn

Reddy

2006

Microfluid Nanofluid

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Organic-aqueous liquid (phenol) extraction is one of many standard techniques to efficiently purify DNA directly from cells. Effective mixing of the two fluid phases increases the surface area over which biological component partitioning may occur. In this work, two phase mixing has been demonstrated in a three inlet microfluidic device geometry. Mixing between the two phases has been achieved by producing an electrohydrodynamic instability at the liquid-liquid interface between the two phases. The initial instability is modeled by considering the small signal linearized analysis for interfacial stresses from both fluid and electrical stress tensors for both inviscid and viscous models. These models predict the onset of instability and the stability criteria over a range of unstable wavenumbers of the mixing process. These models may be applied to relevant microscale geometries, where the unstable wavenumbers and fastest growth wavenumber are determined. At an applied electric field of $8.0·10 5 V/m an instability is experimentally observed by labeling the organic phase with a fluorescent dye and visualizing interfacial perturbations by microscopy. Increasing the electric field increases the instability growth rate and results in an increase of the level of mixing. These results show an increase in conductive fluid entrainment into the nonconducting fluid core measured as a percentage of area of entrainment into the fluorescently labeled organic phase. The entrainment area is seen to increase from 1.9 to 28.6% as the applied field is increased from 8.0·10 5 to 9.0·10 5 V/m. The mixing images are converted into a power spectrum using a fast Hartley transform and the band of unstable wavenumbers of the mixing process are determined. From these results, the theoretical field strengths required to produce these unstable wavenumbers are calculated using the theoretical model, determining the maximum field strength required to excite the largest measured unstable wavenumber. At lower field strengths tested, the theoretically predicted maximum electric field and fastest growth wavenumber compare favorably with the initially applied field and measured fastest growth wavenumber whereas at higher field strengths the theoretical field is much larger than the initially applied field. This is attributed to the larger level of mixing and the ability of the instability to grow beyond the linear range and the field increases as the mixing process occurs due to entrainment of highly conductive fluid decreasing the effective dielectric spacing so that the linearized models underpredict the instability growth rates and interfacial perturbations.

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Electrohydrodynamic mixing and instability induced by co-linear fields and conductivity gradients

Cited by 57 publications

References 5 publications

Convective and absolute electrokinetic instability with conductivity gradients

Convective and absolute electrokinetic instability with conductivity gradients

Electrokinetic instability in microchannel flows: A review

Two phase micromixing and analysis using electrohydrodynamic instabilities

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