Mixing and Flow Transition in an Optimized Electrokinetic Turbulent Micromixer

Abstract

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.

Transition Routes of Electrokinetic Flow in a Divergent Microchannel with Bending Walls

“…The mixing is enhanced as well with small-scale flow structures rapidly developed. When V/m, the EK flow exhibits an ultrafast mixing with fine structures, as shown in Figure 4 f. The evolution of the mixing process is consistent with previous studies [ 21 , 25 ] in flat electrodes scheme, indicating the changing of the micromixer structure will not intrinsically affect the mixing enhancement through EK turbulence.…”

“…The different receptivity of the flow to AC EBF also leads to a different transitional route to chaos and turbulence. Here, we use Hz as an example to show the evolution of the EK flow with an electric Rayleigh number ( , is a dimensionless frequency that represents the ratio of charge relaxation time to AC electric field period, is the kinematic viscosity of fluid, F/m, , and ) [ 25 ]. As shown in Figure 11 , when , shows two peaks relative to that without AC electric field.…”

“…They observed many statistical properties which were believed to exist only in macroscale high Reynolds number turbulence [ 22 , 23 ], such as Kolmogorov −5/3 law of the velocity spectra, Obukhov-Corrsin −5/3 law of the concentration spectra, etc. The EK turbulence leads to a fast mixing of momentum and scalar, especially a mixing length of O (100 µm) [ 24 , 25 ].…”

Analysis of Covarine Particle in Toothpaste Through Microfluidic Simulation, Experimental Validation, and Electrical Impedance Spectroscopy

“…Micromixers play a crucial role in lab-on-a-chip devices that find applications in a range of fields such as chemistry and engineering analysis. − A particular investigation focused on the optimization of a “Y” type electrokinetic turbulent micromixer, revealing that the most effective mixing was achieved in a 350 μm wide micromixer with specific AC electric field conditions [2]. Another study aimed to develop a rapid and robust method for the structural characterization of monoclonal antibodies.…”

Numerical Simulation of the Influence of Non-Uniform ζ Potential on Interfacial Flow

“… is the velocity vector, with , and being the velocity components in , , and directions, respectively, and , and the corresponding unit vectors in Cartesian coordinates (see Figure 1 ). is the electric volume force (EVF), which can be expressed as [ 41 , 42 , 43 ]. where is electric charge density, is the vector of electric field strength.…”