Electroosmotic Flow In Rectangular Microchannel Research Articles

Optimised Electro-Osmotic Flow in Rectangular Microchannels with Smoothed Corners

Electro-osmotic flows are a means of circulating polar fluids through microchannels without resorting to mechanical pumping. The lack of moving parts, of noise and the ease of integration in silicon chips make them an interesting option for microchip cooling and miniaturized total analysis systems. This paper describes an optimization in terms of first- and second-law analysis of the cross-section of a microchannel subject to electro-osmotic flow. Starting from rectangular cross-sections of different aspect ratios, its corners are progressively smoothed and the resulting Poiseuille and Nusselt numbers computed. Performance evaluation criteria are then used to assess the change in, among others, heat transfer rate, temperature difference between wall and bulk fluid, and equivalent pumping power. The entropy number is also computed and the results commented. It is found that the latter criterion highlights a configuration of minimum entropy generation, whereas the trends of the heat transfer and temperature difference are opposite to that of the equivalent pumping power.

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

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.

Electroosmotic flow in rectangular microchannels with Joule heating effects

Experimental studies were conducted on fully developed and steady electroosmotic flow in rectangular microchannels where the channel height (H) to width (W) ratios are varied. The Joule heating and its effects with the changes of the channel aspect ratio (H/W), the applied electric field strength and the type of buffer solutions were examined and data were presented. It is found that the presence of Joule heating and flow area change could have a great impact on the electroosmotic flow (EOF) via the buffer solution temperature rise.

Characterization of electroosmotic flow in rectangular microchannels

In this paper, the electroosmotic displacing process between two solutions (namely the same electrolyte of different concentrations) in a rectangular microchannel is studied theoretically and experimentally. Firstly, the electric potential and velocity field in a rectangular microchannel are obtained by solving the governing equations. Fourier transform method is used to solve the electrolyte concentration profile equation. The electric current versus time curve through the microchannel is predicted based on the concentration profile obtained. The current monitoring technique is then used to study the electroosmotic displacing process. The results from the measured current–time relations agree well with those from the prediction, suggesting a reliable theoretical model developed in this study.

Numerical simulation on influence factors of electroosmotic flow in rectangular microchannel

Aiming at the design parameter optimization prob- lem of the electroosmotic pumping,the mathematic model of electroosmotic flow is made.The coupling equations governing the electric double layer (EDL) field and the velocity field in the cross-section of rectangular microchannels are numerically solved by employing a finite control volume scheme.The de- pendence of the potential,velocity and volumetric flowrate on the aspect ratio,hydraulic diameter,liquid properties and the applied electrical field is analyzed.And the fitting polynomials of the relationships between the volumetric flow,average ve- locity and influence factors are presented.The numerical simu- lation results show that the volumetric flowrate decreases as the aspect ratio increases.When the aspect ratio approaches 1,the volumetric flowrate is minimum.The volumetric flowrate in- creased with the square of hydraulic diameter.The average velocity is dependent on the ionic concentration and the applied electrical field strength.However,the aspect ratio and hydraulic diameter have little impact on the average velocity.

Dynamic aspects of electroosmotic flow in rectangular microchannels

The study presents an analysis of the dynamic aspects of the electroosmotic flow in rectangular microchannels. An analytical solution for electrical potential distribution in the channel is obtained by solving the linearized Poisson–Boltzmann equation under the Debye–Hückel approximation. Dynamic electroosmotic flow field driven by an alternating electric field is solved analytically by using the Green's function method. Parametric studies are carried out to examine the time evolution of the electroosmotic flow under the effects of the channel size, ionic concentration, and zeta potential. Specifically, the effect of frequency-dependent AC electric field on the oscillating electroosmotic flow is discussed. In addition, the solution of the slip velocity approximation based on the Stokes second problem is presented for comparison with the results obtained from the analytical scheme developed in this study.

An experimental study of electro-osmotic flow in rectangular microchannels

Experimental studies were carried out on fully developed and steady electro-osmotic flow in a rectangular channel where the channel height $h$ is comparable to its width and the thickness of the electric double layer characterized by the Debye length is much less than $h$ . The nano-particle image velocimetry technique was used to measure the two components of the velocity field parallel to and within about 100 nm of the channel wall for $h\,{\leq}\,25\,\umu$ m. The mobility of the particle tracers was calculated from averaged velocity data for various electric field strengths. The experimentally determined mobility values are compared with analytical predictions for dilute aqueous solutions of sodium tetraborate.

Numerical solution of electro-osmotic flow in a “flow field effect transistor”

Recently, a general applicable numerical model for the simulation of steady electro-osmotic flow in rectangular micro-channels has been presented and evaluated based on available analytical solutions [Anal. Chem. 74 (19) (2002) 4919]. This model combines the steady multi-ion transport model and the Navier–Stokes equations, and has been implemented in a finite element code. The model includes the ion distribution in the Helmholtz double layer and considers only one single electrical potential field variable throughout the domain. In this paper, the model is further evaluated through comparison with experimental data obtained in a so-called flow field effect transistor or FlowFET [Science 286 (1999) 942]. It has been found that the numerical solutions are in very good agreement with the experimental data and with the commonly used slip boundary condition model.

Liquid transport in rectangular microchannels by electroosmotic pumping

The characteristics of electroosmotic flow in rectangular microchannels were investigated in this paper. A 2D Poisson–Boltzmann equation and the 2D momentum equation were used to model the electric double layer field and the flow field. The numerical solutions show significant influences of the channel cross-section geometry (i.e. the aspect ratio) on the velocity field and the volumetric flow rate. Also, the numerical simulation of the electroosmotic flow reveals how the velocity field and the volumetric flow rate depend on the ionic concentration, zeta potential, channel size and the applied electrical field strength.