Large-Scale Flow in Micro Electrokinetic Turbulent Mixer

Nan, Keyi; Hu, Zhongyan; Zhao, Wei; Wang, Kaige; Bai, Jintao; Wang, Guiren

doi:10.3390/mi11090813

Cited by 9 publications

(6 citation statements)

References 58 publications

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“…They hypothesized that there existed a largescale secondary flow caused by the imbalance of AC electroosmotic flow (ACEOF) near the top and bottom walls. Then, Nan et al 50 observed the 3D flow field using microparticle image velocimetry (μPIV) and verified the existence of a large-scale swirling flow that can enhance entrainment in the μEK turbulent micromixer.…”

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confidence: 99%

Mixing and Flow Transition in an Optimized Electrokinetic Turbulent Micromixer

et al. 2022

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Micromixer is a key element in a lab on a chip for broad applications in the analysis and measurement of chemistry and engineering. Previous investigations reported that electrokinetic (EK) turbulence could be realized in a "Y" type micromixer with a cross-sectional dimension of 100 μm order. Although the ultrafast turbulent mixing can be generated at a bulk flow Reynolds number on the order of unity, the micromixer has not been optimized. In this investigation, we systematically investigated the influence of electric field intensity, AC frequency, electric conductivity ratio, and channel width at the entrance on the mixing effect and transition electric Rayleigh number in the "Y" type electrokinetic turbulent micromixer. It is found that the optimal mixing is realized in a 350 μm wide micromixer, under 100 kHz and 1.14 × 10 5 V/m AC electric field, with an electric conductivity ratio of 1:3000. Under these conditions, a degree of mixedness of 0.93 can be achieved at 84 μm from the entrance and 100 ms. A further investigation of the critical electric field and the critical electric Rayleigh number indicates that the most unstable condition of EK flow instability is inconsistent with that of the optimal mixing in EK turbulence. To predict the evolution of EK flow under high Ra σ and guide the design of EK turbulent micromixers, it is necessary to apply a computational turbulence model instead of linear instability analysis.

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confidence: 99%

Mixing and Flow Transition in an Optimized Electrokinetic Turbulent Micromixer

et al. 2022

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“…Therefore, the mixing of fluids can be enhanced by nonlinear EK flow induced near electrodes. Besides, due to the unbalanced electric field on the low and high electric conductivity streams, a large scale vortical flow can be generated by the electro-osmotic flow (EOF) adjacent to the top and bottom walls, as have been investigated by Nan et al [25]. The vortical flow could significantly enhance the 3D mixing of fluids on large scales.…”

Section: Electric Field Effectmentioning

confidence: 99%

“…Recently, many works on electrokinetic instability (EKI) were accomplished and attracted much attention, it is a phenomenon described by charge accumulation at perturbed interfaces due to electrical conductivity gradients, which exist in the bulk flow [16][17][18][19][20]. Although many significant results have already been obtained through those previous works [21][22][23][24][25], much effort is still needed to improve our understanding of electrokinetic mixing under AC electric field, to make the electrokinetic micromixers more efficient and flexible for "lab-on-a-chip" applications.…”

Section: Introductionmentioning

confidence: 99%

Rapid AC Electrokinetic Micromixer with Electrically Conductive Sidewalls

et al. 2021

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We report a quasi T-channel electrokinetics-based micromixer with electrically conductive sidewalls, where the electric field is in the transverse direction of the flow and parallel to the conductivity gradient at the interface between two fluids to be mixed. Mixing results are first compared with another widely studied micromixer configuration, where electrodes are located at the inlet and outlet of the channel with electric field parallel to bulk flow direction but orthogonal to the conductivity gradient at the interface between the two fluids to be mixed. Faster mixing is achieved in the micromixer with conductive sidewalls. Effects of Re numbers, applied AC voltage and frequency, and conductivity ratio of the two fluids to be mixed on mixing results were investigated. The results reveal that the mixing length becomes shorter with low Re number and mixing with increased voltage and decreased frequency. Higher conductivity ratio leads to stronger mixing result. It was also found that, under low conductivity ratio, compared with the case where electrodes are located at the end of the channel, the conductive sidewalls can generate fast mixing at much lower voltage, higher frequency, and lower conductivity ratio. The study of this micromixer could broaden our understanding of electrokinetic phenomena and provide new tools for sample preparation in applications such as organ-on-a-chip where fast mixing is required.

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“…One of the most explored approaches for trying to achieve turbulent flow characteristics in microchannels is the use of electrokinetic forcing [9,10]. For example, as argued by the authors, Wang et al [11] have reported a direct observation of the existence of "turbulence" in microfluidics with Re ∼ 1 in a pressure-driven flow under electrokinetic forcing using a novel velocimeter with ultrahigh spatiotemporal resolution.…”

Section: Nomenclaturementioning

confidence: 99%

Thermophysical Analysis of Microconfined Turbulent Flow Regimes at Supercritical Fluid Conditions in Heat Transfer Applications

Bernades

Jofre

2022

Journal of Heat Transfer

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The technological opportunities enabled by understanding and controlling microscale systems have not yet been capitalized to disruptively improve energy processes. The main limitation corresponds to the laminar flows typically encountered in microdevices, which result in small mixing and transfer rates. This is a central unsolved problem in the thermal-fluid sciences, in what some researchers refer to as “quot;ab-on-a-chip and energy - microfluidic frontier”. Therefore, this work focuses on analyzing the potential of supercritical fluids to achieve turbulence in microconfined systems by studying their thermophysical properties. In particular, a real-gas thermodynamic model, combined with high-pressure transport coefficients, is utilized to characterize the Reynolds number achieved as a function of supercritical pressures and temperatures. The results indicate that fully-turbulent flows can be attained for a wide range of working fluids related to heat transfer applications, power cycles and energy conversion systems, and presenting increment ratios of O(100) with respect to atmospheric (subcritical) thermodynamic conditions. The underlying physical mechanism to achieve relatively high Reynolds numbers is based on operating within supercritical thermodynamic states (close to the critical point and pseudo-boiling region) in which density is relatively large while dynamic viscosity is similar to that of a gas. In addition, based on the Reynolds numbers achieved and the thermophysical properties of the fluids studied, an assessment of heat transfer at turbulent microfluidic conditions is presented to demonstrate the potential of supercritical fluids to enhance the performances of standard microfluidic systems by factors up to approximately 50x.

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Large-Scale Flow in Micro Electrokinetic Turbulent Mixer

Cited by 9 publications

References 58 publications

Mixing and Flow Transition in an Optimized Electrokinetic Turbulent Micromixer

Mixing and Flow Transition in an Optimized Electrokinetic Turbulent Micromixer

Rapid AC Electrokinetic Micromixer with Electrically Conductive Sidewalls

Thermophysical Analysis of Microconfined Turbulent Flow Regimes at Supercritical Fluid Conditions in Heat Transfer Applications

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