Transient electroosmotic flow induced by AC electric field in micro-channel with patchwise surface heterogeneities

Luo, Win‐Jet

doi:10.1016/j.jcis.2005.09.052

Cited by 30 publications

(15 citation statements)

References 21 publications

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“…Through a numerical investigation, Lee et al [24] demonstrated various kinds of flow circulation in a circular slit with time-periodic EOF for non-uniform zeta potential distribution along the microchannel walls. Luo [25] numerically investigated the transient electroosmotic flow induced by an alternating electric field with patch-wise surface heterogeneities in a planner microchannel. Tang et al [26] studied the pulsating electroosmotic flow in a planar microchannel with non-uniform surface charges by the lattice Boltzmann method.…”

Section: Introductionmentioning

confidence: 99%

Analytical Solution of Time-Periodic Electroosmotic Flow through Cylindrical Microchannel with Non-Uniform Surface Potential

Khan

Dutta

2019

Micromachines

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Time-periodic electroosmotic flow (EOF) with heterogeneous surface charges on channel walls can potentially be used to mix species or reagent molecules in microfluidic devices. Although significant research efforts have been placed to understand different aspects of EOF, its role in the mixing process is still poorly understood, especially for non-homogeneous surface charge cases. In this work, dynamic aspects of EOF in a cylindrical capillary are analyzed for heterogeneous surface charges. Closed form analytical solutions for time-periodic EOF are obtained by solving the Navier–Stokes equation. An analytical expression of induced pressure is also obtained from the velocity field solution. The results show that several vortices can be formed inside the microchannel with sinusoidal surface charge distribution. These vortices change their pattern and direction as the electric field change its strength and direction with time. In addition, the structure and strength of the vorticity depend on the frequency of the external electric field and the size of the channel. As the electric field frequency or channel diameter increases, vortices are shifted towards the channel surface and the perturbed flow region becomes smaller, which is not desired for effective mixing. Moreover, the number of vorticities depends on the periodicity of the surface charge.

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Section: Introductionmentioning

confidence: 99%

Analytical Solution of Time-Periodic Electroosmotic Flow through Cylindrical Microchannel with Non-Uniform Surface Potential

Khan

Dutta

2019

Micromachines

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“…Therefore, numerical or experimental studies should be conducted for solution of complete non-linear equations or for flow in more complicated situations. Luo applied numerical techniques to solve the P-B equation for transient AC and DC electro-osmotic flow in a curved rectangular microtube [16] and parallel plates with patchwise surface heterogeneities [17]. Yang et al [18] also presented numerical solutions for the entry region of transient electro-osmosis between two large parallel plates.…”

Section: Introductionmentioning

confidence: 99%

A numerical investigation of transient electro-osmotic flow in rectangular microchannels: A comparison of different models

Kamali

Eslami

2010

Proceedings of the Institution of Mechanical Engineers, Part C:

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Transient electro-osmotic flow in rectangular microchannels is investigated numerically in this article. The complete Poisson—Boltzmann equation along with the time-dependent momentum equation is solved using the finite-difference method. Moreover, linearized equations based on the Debye—Huckle assumption are also solved to compare with the available analytical approximate solutions. The effects of different parameters such as wall zeta potential, non-dimensional electrokinetic width, and channel aspect ratio are also studied. It is shown that the Debye—Huckle approximation is not only valid for small values of zeta potential, but also the channel hydraulic diameter should be large enough with respect to electrical double layer (EDL) thickness. In addition, the flow behaviour at higher values of zeta potential is shown to be completely different from what available analytical solutions predict. Effective parameters on the transition period from the start time to the steady-state condition are also discussed. On the other hand, a comparison between the present numerical solution and the results of slip velocity approximation reveals that the slip model could be only used for very large values of non-dimensional electro-kinetic width. Finally, velocity distributions in channels of different aspect ratios are provided and discussed.

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“…By inducing a multiple stretching-folding effect within the microchannel, sample mixing could be achieved within 100*300 ms (Branerbjerg et al 1996). Researchers have also explored the feasibility of achieving species mixing by patterning the microchannel walls with a heterogeneous surface charge (Ajdari 1995; Qian and Bau 2002;Erickson and Li 2002;Biddiss et al 2004). Luo (2006 and Luo et al (2007) applied an external AC electrical field to a microchannel with patchwise surface heterogeneities, enabled a significant reduction in both the mixing channel length and the retention time.…”

Section: Introductionmentioning

confidence: 99%

Effect of ionic concentration on electrokinetic instability in a cross-shaped microchannel

Luo

2008

Microfluid Nanofluid

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This paper performs numerical and experimental investigations into electrokinetic instability (EKI) effects to accomplish mixing of multiple solutions with different electric conductivities in a cross-shaped microchannel. This study considers two multiple-species, namely two aqueous electrolyte solutions and three electrolyte solutions with conductivity ratios ranging between 1 and 10, respectively. A stratified flow condition is formed when the intensity of the applied DC electrical field is below a certain threshold value. However, as the intensity increased, various EKI phenomena are induced, including a series of flow recirculations at the interfaces of neighboring species flows, a string of pearl-like flow structures aligned with the low-conductivity species stream, and a wavy perturbation of the species interfaces. The EKI phenomena are clarified in terms of the respective axial velocities and specie flow pressure gradients. In practice, the nature of the EKI effect depends upon the relative directions of the conductivity gradients within the microchannel. Analyzing the EKI phenomena effects in mixing multiple-species, it is found that the mixing performance obtained when the conductivity gradients are orientated in opposing directions is higher than that achieved when the conductivity gradients are aligned. Furthermore, the optimal mixing index is achieved when the conductivity gradients are directed away from one another (i.e. from the center of the microchannel toward the microchannel walls) rather than toward one another (i.e. from the microchannel walls toward the center of the microchannel).

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Transient electroosmotic flow induced by AC electric field in micro-channel with patchwise surface heterogeneities

Cited by 30 publications

References 21 publications

Analytical Solution of Time-Periodic Electroosmotic Flow through Cylindrical Microchannel with Non-Uniform Surface Potential

Analytical Solution of Time-Periodic Electroosmotic Flow through Cylindrical Microchannel with Non-Uniform Surface Potential

A numerical investigation of transient electro-osmotic flow in rectangular microchannels: A comparison of different models

Effect of ionic concentration on electrokinetic instability in a cross-shaped microchannel

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