Pulsating Electroosmotic Flow and Wall Block Mixing in Microchannels

2008 ◽  
Author(s):  
G. H. Tang ◽  
X. J. Gu ◽  
R. W. Barber ◽  
D. R. Emerson ◽  
Y. H. Zhang ◽  
...  
Keyword(s):  
Electroosmotic Flow ◽  
Fluid Motion ◽  
Pulsating Flow ◽  
Practical Significance ◽  
Mixing Efficiency ◽  
Heterogeneous Surfaces ◽  
Microfluidic Systems ◽  
Navier Stokes Equation ◽  
Design And Optimization ◽  
Poisson Boltzmann Equation

Understanding electroosmotic flow in microchannels is of both fundamental and practical significance for the design and optimization of various microfluidic devices to control fluid motion. Electroosmotic flows in microfluidic systems are restricted to the low Reynolds number regime, and mixing in these systems becomes problematic due to negligible inertial effects. To enhance the species mixing effect, the current study presents a numerical investigation of steady-state electroosmotic flow mixing in smooth microchannels, channels patterned with surface blocks, channels patterned with heterogeneous surfaces, as well as pulsating electroosmotic flow. The lattice Boltzmann equations, which recover the nonlinear Poisson-Boltzmann equation, the Navier-Stokes equation including the external force term, and the diffusion equation, were solved to obtain the electric potential distribution in the electrolyte, the velocity field, and the species concentration distribution, respectively. The simulation results confirm that wall blocks, heterogeneous surfaces, and electroosmotic pulsating flow can all change the flow pattern and enhance mixing in microfluidic systems. In addition, it is shown that pulsating flow provides the most promising method for enhancing the mixing efficiency.

Numerical Analysis of Micro-Mixing in Rough Microchannels

2011 ◽  
Vol 189-193 ◽  
pp. 1452-1455 ◽  
Author(s):  
Da Yong Yang
Keyword(s):  
Electroosmotic Flow ◽  
Roughness Element ◽  
Fluid Motion ◽  
Microfluidic Devices ◽  
Practical Significance ◽  
Mixing Efficiency ◽  
The Finite Element Method ◽  
Governing Equations ◽  
Design And Optimization ◽  
Control Fluid

Understanding the micro-mixing of electroosmotic flow is of both fundamental and practical significance for the design and optimization of various microfluidic devices to control fluid motion. In this paper, the governing equations of the micro-mixing in rough microchannels with rectangle surface roughness are solved using the finite element method and the effects of roughness height and space on mixing efficiency are investigated. The results indicate that the effects cannot be ignored and the mixing efficiency increases with the roughness element height and density.

Frequency Dependent Velocity and Vorticity Fields of Electroosmotic Flow in a Closed-End Rectangular Microchannel

2004 ◽  
Author(s):  
Marcos
Keyword(s):  
Electroosmotic Flow ◽  
Navier Stokes ◽  
Vorticity Field ◽  
Navier Stokes Equation ◽  
Rectangular Microchannel ◽  
Layer Potential ◽  
Frequency Dependent ◽  
Variable Approach ◽  
Poisson Boltzmann ◽  
Poisson Boltzmann Equation

The frequency dependent electroosmotic flow in a closed-end rectangular microchannel is analyzed in this study. Dynamic AC electroosmotic flow field is obtained analytically by solving the Navier-Stokes equation using the Green’s function formulation in combination with a complex variable approach. With the Debye-Hu¨ckel approximation, the electrical double layer potential distribution in the channel is obtained by analytically solving the linearized two-dimensional Poisson-Boltzmann equation. Additionally, the Onsager’s principle of reciprocity is demonstrated to be valid for AC electroosmotic flow. The effects of frequency-dependent AC electric field on the oscillating electroosmotic flow and the induced backpressure gradient are studied. Furthermore, the expression for the electroosmotic vorticity field is derived, and the characteristic of the vorticity field in AC electroosmotic flow is discussed. Based on the Stokes second problem, the solution of the slip velocity approximation is also presented for comparison with the results obtained from the analytical solution developed in this study.

Transient Electroosmotic Flow in Slit Microchannel Containing Salt-Free Medium

2009 ◽  
Author(s):  
Shih-Hsiang Chang
Keyword(s):  
Surface Charge Density ◽  
Electroosmotic Flow ◽  
Theoretical Study ◽  
Capillary Tube ◽  
Navier Stokes ◽  
Free Medium ◽  
Navier Stokes Equation ◽  
Poisson Boltzmann ◽  
Flow Through ◽  
Poisson Boltzmann Equation

A theoretical study on the transient electroosmotic flow through a slit microchannel containing a salt-free medium is presented for both constant surface charge density and constant surface potential. The exact analytical solutions for the electric potential distribution and the transient electroosmotic flow velocity are derived by solving the nonlinear Poisson-Boltzmann equation and the Navier-Stokes equation. Based on these results, a systematic parametric study on the characteristics of the transient electroosmotic flow is detailed. The general behavior of electroosmotic flow in a planar slit is similar to that in a capillary tube; however, the rate of evolution of the flow in a tube with time is faster by a factor of about 2.4 than that in a slit with its width equal to the tube diameter.

scholarly journals Geometric Design-based Dimensional Synthesis of a Novel Metamorphic Multi-fingered Hand with Maximal Workspace

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Wei An ◽  
Jun Wei ◽  
Xiaoyu Lu ◽  
Jian S. Dai ◽  
Yanzeng Li
Keyword(s):  
Geometric Design ◽  
Practical Significance ◽  
Design Parameters ◽  
Control Algorithms ◽  
Discretization Method ◽  
Dimensional Synthesis ◽  
Symmetrical Structure ◽  
Design And Optimization ◽  
Total Length

AbstractCurrent research on robotic dexterous hands mainly focuses on designing new finger and palm structures, as well as developing smarter control algorithms. Although the dimensional synthesis of dexterous hands with traditional rigid palms has been carried out, research on the dimensional synthesis of dexterous hands with metamorphic palms remains insufficient. This study investigated the dimensional synthesis of a palm of a novel metamorphic multi-fingered hand, and explored the geometric design for maximizing the precision manipulation workspace. Different indexes were used to value the workspace of the metamorphic hand, and the best proportions between the five links of the palm to obtain the optimal workspace of the metamorphic hand were explored. Based on the fixed total length of the palm member, four nondimensional design parameters that determine the size of the palm were introduced; through the discretization method, the influence of the four design parameters on the workspace of the metamorphic hand with full-actuated fingers and under-actuated fingers was analyzed. Based on the analysis of the metamorphic multi-fingered hand, the symmetrical structure of the palm was designed, resulting in the largest workspace of the multi-fingered hand, and proved that the metamorphic palm has a massive upgrade for the workspace of underactuated fingers. This research contributed to the dimensional synthesis of metamorphic dexterous hands, with practical significance for the design and optimization of novel metamorphic hands.

The Design and Simulation for a Novel Electroosmotic Micromixer

2006 ◽  
Author(s):  
Hongjun Song ◽  
Xie-Zhen Yin ◽  
Dawn J. Bennett
Keyword(s):  
Electric Field ◽  
Cross Section ◽  
Chemical Reactions ◽  
Electroosmotic Flow ◽  
Chaotic Advection ◽  
Microfluidic Systems ◽  
Mixing Effect ◽  
Passive Mixers ◽  
The Cross ◽  
External Forces

The analysis of fluid mixing in microfluidic systems is useful for many biological and chemical applications at the micro scale such as the separation of biological cells, chemical reactions, and drug delivery. The mixing of fluids is a very important factor in chemical reactions and often determines the reaction velocity. However, the mixing of fluids in microfluidics tends to be very slow, and thus the need to improve the mixing effect is a critical challenge for the development of the microfluidic systems. Micromixers can be classified into two types, active micromixers and passive micromixers. Passive micromixers depend on changing the structure and shape of microchannels in order to generate chaotic advection and to increase the mixing area. Thus, the mixing effect is enhanced without any help from external forces. Although passive micromixers have the advantage of being easily fabricated and requiring no external energy, there are also some disadvantages. For example, passive mixers often lack flexibility and power. Passive mixers rely on the geometrical properties of the channel shapes to induce complicated fluid particle trajectories thereby enhancing the mixing effect. On the other hand, active micromixers induce a time-dependent perturbation in the fluid flow. Active micromixers mainly use external forces for mixing including ultrasonic vibration, dielectrophoresis, magnetic force, electrohydrodynamic, and electroosmosis force. However, the complexity of their fabrication limits the application of active micromixers. In this paper we present a novel electroosmotic micromixer using the electroosmotic flow in the cross section to enhance the mixing effect. A DC electric field is applied to a pair of electrodes which are placed at the bottom of the channel. A transverse flow is generated in the cross section due to electroosmotic flow. Numerical simulations are investigated using a commercial software Fluent® which demonstrates how the device enhances the mixing effect. The mixing effect is increased when the magnitude of the electric field increased. The influences of Pe´clet number are also discussed. Finally, a simple fabrication using polymeric materials such as SU-8 and PDMS is presented.

scholarly journals Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index

Micromachines ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1055
Author(s):  
Alireza Farahinia ◽  
Jafar Jamaati ◽  
Hamid Niazmand ◽  
Wenjun Zhang
Keyword(s):  
Reynolds Number ◽  
Zeta Potential ◽  
Electroosmotic Flow ◽  
Molecular Diffusion ◽  
Slip Surface ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Slip Coefficient ◽  
Mixing Rate ◽  
Heterogeneous Distribution

One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz–Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.

scholarly journals Closed-Form Non-Stationary Solutionsfor Thermo and Chemovibrational Viscous Flows

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 175 ◽  
Author(s):  
Dmitry Bratsun ◽  
Vladimir Vyatkin
Keyword(s):  
Viscous Flow ◽  
Closed Form ◽  
General Procedure ◽  
Fluid Velocity ◽  
Fluid Motion ◽  
Boussinesq Approximation ◽  
Navier Stokes ◽  
Chemical Transformations ◽  
Navier Stokes Equation ◽  
Harmonic Vibrations

A class of closed-form exact solutions for the Navier–Stokes equation written in the Boussinesq approximation is discussed. Solutions describe the motion of a non-homogeneous reacting fluid subjected to harmonic vibrations of low or finite frequency. Inhomogeneity of the medium arises due to the transversal density gradient which appears as a result of the exothermicity and chemical transformations due to a reaction. Ultimately, the physical mechanism of fluid motion is the unequal effect of a variable inertial field on laminar sublayers of different densities. We derive the solutions for several problems for thermo- and chemovibrational convections including the viscous flow of heat-generating fluid either in a plain layer or in a closed pipe and the viscous flow of fluid reacting according to a first-order chemical scheme under harmonic vibrations. Closed-form analytical expressions for fluid velocity, pressure, temperature, and reagent concentration are derived for each case. A general procedure to derive the exact solution is discussed.

Thermally Fully Developed Electroosmotic Flow of Power-Law Fluids in a Circular Microchannel

2013 ◽  
Vol 29 (4) ◽  
pp. 609-616 ◽  
Author(s):  
Y.-J. Sun ◽  
Y.-J. Jian ◽  
L. Chang ◽  
Q.-S. Liu
Keyword(s):  
Power Law ◽  
Joule Heating ◽  
Electroosmotic Flow ◽  
Flow Behavior ◽  
Mathematic Model ◽  
Dimensionless Temperature ◽  
Fluid Temperature ◽  
Navier Stokes Equation ◽  
Power Law Fluids ◽  
Behavior Index

ABSTRACTThis study presents a thermally fully developed electroosmotic flow of the non-Newtonian power-law fluids through a circle microchannel. A rigorous mathematic model for describing the Joule heating in an electroosmotic flow including the Poisson Boltzmann equation, the modified Navier Stokes equation and the energy equation is developed. The semi-analytical solutions of normalized velocity and temperature are derived. The velocity profile is computed by numerical integrate, and the temperature distribution is obtained by finite difference method. Results show that the velocity profiles depend greatly on the fluid behavior index n and the nondimensional electrokinetic width K. For a specified value of K, the axial velocity increases with a decrease in n, and the same trend for the effect of K on the velocity can be found for a specified value of n. Moreover, the dimensionless temperature is governed by three parameters, namely, the flow behavior index n, the nondimensional electrokinetic width K, and the dimen-sionless Joule heating parameter G. The variations of radial fluid temperature distributions with different parameters are investigated.

Control of Flow Field, Mass Transfer and Mixing Enhancement in T-Shaped Microchannels

2016 ◽  
Vol 33 (3) ◽  
pp. 387-394
Author(s):  
Y. Bazargan-Lari ◽  
S. Movahed ◽  
M. Mashhoodi
Keyword(s):  
Flow Field ◽  
Applied Voltage ◽  
Electroosmotic Flow ◽  
Microfluidic Devices ◽  
Mixing Efficiency ◽  
Mixing Enhancement ◽  
Field Mass ◽  
Control Of Flow ◽  
Micro Mixer ◽  
Two Fluid

AbstractA T-shaped microfluidic micro-mixer was designed to mix desired concentrations of two fluid streams and to prepare their homogenous mixture solution. A hydrostatic pressure gradient was induced in one of the branches of the system (mixing channel) by applying external electric field and generating electroosmotic flow in the two other branches of the system. The flow field and transferred mass into the mixing channel can be regulated by controlling the applied voltage of the system. In order to prepare more homogenous mixture solution, some obstacles were added to the mixing channel to induce perturbation in the flow field and enhance the mixing efficiency of the system. Numerical simulations were performed to show the correctness of the proposed mixing strategy and to investigate the influences of the applied voltage on the mixing efficiency and induced pressure flow in the mixing channel. A proposed design can be used as a guideline to control and enhance mixing efficiency, and consequently functionality, of different microfluidic devices.

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