Inverse Problems in Non-Newtonian Electrokinetic Flows in Microchannel Networks

Volume 3 ◽  
2004 ◽  
Author(s):  
William B. Zimmerman ◽  
Julia M. Rees ◽  
Thomas J. Craven
Keyword(s):  
Slip Velocity ◽  
Pressure Profile ◽  
Carreau Fluid ◽  
Boundary Slip ◽  
Electrokinetic Flow ◽  
Nonlinear Viscosity ◽  
Relaxation Time Scale ◽  
Electrokinetic Flows ◽  
Electrokinetic Motion ◽  
End Wall

A model of the electrokinetic flow of a fluid with a nonlinear viscosity of the Carreau type is simulated by finite element methods in a microchannel T-junction. The simulations accelerate the fluid from rest using the model for boundary slip velocity imposed due to a Debye double layer motion proposed by Zimmerman and MacInnes (2003). The simulations demonstrate an interval of the transient evolution of the end wall pressure profile that scales proportionally with the Reynolds number. The shape of the steady state profile is shown to be sensitive to the relaxation time scale characterizing the shear rate dependence of a Carreau fluid. Consequently, this flow regime can be taken as a paradigm viscometric flow for electrokinetic motion.

scholarly journals Comparison of the Influences of Surface Texture and Boundary Slip on Tribological Performances

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Qiyin Lin ◽  
Baotong Li
Keyword(s):  
Surface Texture ◽  
Slip Velocity ◽  
Structure Parameters ◽  
Textured Surfaces ◽  
Slider Bearing ◽  
Boundary Slip ◽  
Surface Textures ◽  
Slip Surfaces ◽  
Texture Structure ◽  
The Relationship

Close attentions have been widely paid to the engineering textured and slip surfaces for improving bearing tribological performances. Comparison studies on the tribological characteristics of slip and textured surfaces are carried out in this work. The analysis results point out that the influences of surface texture and boundary slip on tribological performances of slider bearing are strongly similar. For the determinate surface textures, there is one and only value of slip velocity to make the tribological performances of textured and slip surfaces in agreement. The corresponding relation between the slip velocity and the texture structure parameters is also obtained, and the size of slip velocity is directly related to the texture geometry parameters including its position parameters. This study will help us to further understand the relationship between boundary slip and surface texture and also the slip phenomenon.

scholarly journals A depth-averaged electrokinetic flow model for shallow microchannels

2008 ◽  
Vol 608 ◽  
pp. 43-70 ◽  
Author(s):  
HAO LIN ◽  
BRIAN D. STOREY ◽  
JUAN G. SANTIAGO
Keyword(s):  
Electromechanical Coupling ◽  
Three Dimensional ◽  
Momentum Equation ◽  
Width Ratio ◽  
Complex Flow ◽  
Electrokinetic Flow ◽  
Plane Flow ◽  
Depth Direction ◽  
Averaged Equations ◽  
Electrokinetic Flows

Electrokinetic flows with heterogeneous conductivity configuration occur widely in microfluidic applications such as sample stacking and multidimensional assays. Electromechanical coupling in these flows may lead to complex flow phenomena, such as sample dispersion due to electro-osmotic velocity mismatch, and electrokinetic instability (EKI). In this work we develop a generalized electrokinetic model suitable for the study of microchannel flows with conductivity gradients and shallow-channel geometry. An asymptotic analysis is performed with the channel depth-to-width ratio as a smallness parameter, and the three-dimensional equations are reduced to a set of depth-averaged equations governing in-plane flow dynamics. The momentum equation uses a Darcy–Brinkman–Forchheimer-type formulation, and the convective–diffusive transport of the conductivity field in the depth direction manifests itself as a dispersion effect on the in-plane conductivity field. The validity of the model is assessed by comparing the numerical results with full three-dimensional direct numerical simulations, and experimental data. The depth-averaged equations provide the accuracy of three-dimensional modelling with a convenient two-dimensional equation set applicable to a wide class of microfluidic devices.

Analysis of the pressure buildup behind rigid porous media impinged by shock waves in time and frequency domains

2015 ◽  
Vol 779 ◽  
pp. 842-858 ◽  
Author(s):  
O. Ram ◽  
O. Sadot
Keyword(s):  
Porous Medium ◽  
Shock Waves ◽  
Shock Tube ◽  
Pressure Profile ◽  
Air Gap ◽  
Front Face ◽  
Porous Sample ◽  
Rear Face ◽  
Pressure Buildup ◽  
End Wall

The transformation of a time-dependent pressure pulse imposed on the front face of a rigid porous medium sample, mounted in a tunnel, through the sample and a fixed-volume air gap between the rear face of the sample and the end wall of a tunnel is studied both experimentally and analytically. In the experiments, rigid porous samples that are placed at various distances from a shock tube end wall are subjected to the impingement of shock waves. The pressure buildup behind the porous sample is monitored and compared with the pressure imposed at the front face of the porous sample. The shock tube is fitted with a short driver section in order to generate blast-like decaying pressure profiles, which continue to decay after the initial shock impingement. In this scenario, the measured pressure profile at the end wall, which is affected by the properties of the porous medium and the size of the air gap separating its rear face and the shock tube end wall, is significantly different from the pressure profile imposed on the front face of the porous sample. The mechanism governing the pressure transformation provided by the porous medium is attributed to a selective filtration process that attenuates the pressure changes associated with high frequencies. The results of the present study are also analysed in conjunction with previously published analytical and numerical models to achieve a broader understanding of the physical mechanisms affecting the pressure buildup.

Study of Nanoscale Pressure-Driven Electrokinetic Flow with Effects of Wall Lattice Plane

2009 ◽  
Vol 25 (4) ◽  
pp. 363-378 ◽  
Author(s):  
T.-H. Yen ◽  
C.-Y. Soong ◽  
P.-Y. Tzeng
Keyword(s):  
Charge Density ◽  
Flow Characteristics ◽  
Continuum Theory ◽  
Face Centered Cubic ◽  
Electrokinetic Flow ◽  
Solvent Model ◽  
Analytic Expressions ◽  
Lattice Planes ◽  
Electrokinetic Flows ◽  
Pressure Driven

ABSTRACTThe objective of the present study is to explore pressure-driven flows with the presence of electric double layer (EDL) in nanochannels of various wall lattice planes. Three face-centered cubic (fcc) lattice planes, i.e. fcc(111), fcc(100), and fcc(110), of the channel wall are considered. The structure of diffuse EDL and electrokinetic flow characteristics are dealt with in an atomistic view. Fluid and charge density layering phenomena and their influences on the Stern layer are investigated with the molecular dynamic simulation results. In most of the simulations, a monatomic molecule, W, is used as the solvent model and the charged particles W+ and W− of the same size as the ions. To examine behaviors of the dissimilar particles, a simulation with the aqueous model W for fluid, Na+ for cation and Cl− for anion is also performed. Effects of ion concentrations, wall-fluid interaction energy, and surface charge density on the electro-hydrodynamics are studied. In addition, based on the continuum theory, two analytic expressions for zeta potential with the presence of fluid slippage are derived and analyzed. The present results disclose interesting physics about the influences of wall lattice-fluid interactions, which are significant in further understanding and applications of the nanoscale electrokinetic flows.

Electrokinetic Flow and Measure Method in Microfluidic

2013 ◽  
Vol 275-277 ◽  
pp. 649-653 ◽  
Author(s):  
Lei Gong ◽  
Jian Kang Wu ◽  
Bo Chen
Keyword(s):  
Stokes Equations ◽  
Solid Wall ◽  
Streaming Potential ◽  
Navier Stokes ◽  
Electrokinetic Flow ◽  
Navier Stokes Equations ◽  
Electroviscous Effect ◽  
Poisson Boltzmann Equation ◽  
Electrokinetic Flows ◽  
Pressure Driven

An analytical solution for pressure-driven electrokinetic flows in a narrow capillary is presented based on the Poisson–Boltzmann equation for electrical double layer and the Navier–Stokes equations for incompressible viscous fluid. The analytical solutions indicate that pressure-driven flow of an electrolyte solution in microchannel with charged solid wall induces a streaming potential, which is proportional to the flowrate and induces an electroviscous effect on flow. A device for measuring the electrokinetic flow rate and streaming potential is proposed.

Nonlinear Smoluchowski slip velocity and micro-vortex generation

2002 ◽  
Vol 461 ◽  
pp. 229-238 ◽  
Author(s):  
Y. BEN ◽  
H.-C. CHANG
Keyword(s):  
Electric Field ◽  
Slip Velocity ◽  
Slip Length ◽  
Ionic Flux ◽  
Electrokinetic Flow ◽  
Surface Polarization ◽  
Counter Ions ◽  
Normal Electric Field ◽  
Porous Granule ◽  
Polarized Surface

When an electric field is applied across a conducting and ion-selective porous granule in an electrolyte solution, a polarized surface layer with excess counter-ions is created. The depth of this layer and the overpotential V across this layer are functions of the normal electric field j on the granule surface. By transforming the ionic flux equations and the Poisson equation into the Painlevé equation of the second type and by analysing the latter's asymptotic solutions, we derive a linear universal j–V correlation at large flux with an electrokinetic slip length β. The flux-induced surface polarization produces a nonlinear Smoluchowski slip velocity that can couple with the granule curvature to produce micro-vortices in micro-devices. Such vortices are impossible in irrotational electrokinetic flow with a constant zeta-potential and a linear slip velocity.

Measurement of Transient Electrokinetic Flow in Microchannels Using Micro-PIV Technique

2006 ◽  
Author(s):  
Deguang Yan ◽  
Chun Yang ◽  
Nam-Trung Nguyen ◽  
Xiaoyang Huang
Keyword(s):  
Zeta Potential ◽  
Measurement Data ◽  
Ccd Camera ◽  
Electrokinetic Flow ◽  
Full Field ◽  
Micro Piv ◽  
Piv Technique ◽  
Piv Measurement ◽  
Electrokinetic Flows ◽  
Electroosmotic Velocity

Measurement of the steady-state electroosmotic velocity distributions in microchannels has been reported in the literature. Characterizing time-dependent electrokinetic flows is of importance to the development of microfluidic devices such as rapid capillary electrophoretic separation systems, AC pumps, novel micromixers etc. In this paper, we report a novel technique for studying and quantifying the transient electrokinetic flow phenomena in microchannels using the micro-PIV system with an ordinary PIV CCD camera. This is achieved by synchronizing different trigger signals for the laser, CCD camera, and custom high-voltage switch. Using the transient micro-PIV technique, we further propose a method to determine the electrophoretic component in the particle velocity and the zeta potential of the channel wall. Then the time evolution of the full-field, electroosmotic velocity distributions in both open- and closed-end rectangular microchannels is obtained from the micro-PIV measurement data. Using the slip velocity approach and the measured channel zeta potential, the theoretical predictions of the transient electroosmotic flow in the open- and closed-end microchannels are obtained, and they are found in good agreement with the experimental results.

Electrokinetic energy conversion through cylindrical microannulus with periodic heterogeneous wall potentials

2021 ◽  
Author(s):  
Xin Chu ◽  
Yongjun Jian
Keyword(s):  
Energy Conversion ◽  
Conversion Efficiency ◽  
Fluid Velocity ◽  
Streaming Potential ◽  
Energy Conversion Efficiency ◽  
Mixing Efficiency ◽  
Electrokinetic Flow ◽  
Wall Potential ◽  
Flow Through ◽  
Electrokinetic Flows

Abstract In microfluidic electrokinetic flows, heterogeneous wall potentials are often required to fulfill some functions, such as increasing dispersion and mixing efficiency. In this paper, we study the pressure-driven electrokinetic flow through microannulus with heterogeneous wall potentials in circumferential direction. The streaming potential induced by the ions accumulating in downstream of the microannulus is considered and the electrokinetic energy conversion efficiency is further investigated. Interestingly, based on the method of Fourier expansion, the analytical solutions of fluid velocity, streaming potential and energy conversion efficiency are derived for arbitrary peripheral distribution of the small wall potential for the first time. Four specific patterned modes of the heterogeneous wall potential, i.e., constant, step, sinusoid with period 2π and sinusoid with period π/2 are represented. The distributions of the electric potential and the velocity for four different modes are depicted graphically. Furthermore, the variations of the streaming potential and the electrokinetic energy conversion efficiency with related parameters are also discussed. Results show that when these integral values from -π to π associated with the wall potentials are identical, the streaming potential and the electrokinetic energy conversion efficiency corresponding to different modes are the same. Additionally, the amplitude of fluid velocity peripherally reduces with the increase of the wavenumber of wall potential distribution in θ-direction.

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