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Chun Yang - One of the best experts on this subject based on the ideXlab platform.

  • Combined Pressure-Driven Flow and Electroosmotic Flow
    2014
    Co-Authors: Chun Yang, Deguang Yan
    Abstract:

    Pressure-driven Flow is bulk fluid motion resulting from either a globally applied difference (gradient) or an internally induced hydraulic pressure difference (gradient). Electroosmotic Flow is the bulk liquid motion due to the interaction between an external electric field applied tangentially along a charged surface and the excess net charges in the electric double layer of such a charged surface. Specifically, the focus of this entry will be on the Electroosmotic Flow generated by an applied DC electric field only. In addition, the analysis of this entry is based on an assumption that the order of magnitude of the Electroosmotic Flow velocity is the same as that of the pressure-driven Flow velocity. In the field of microand nanofluidics, the term combined pressure-driven Flow and Electroosmotic Flow is referred to as the bulk liquid Flow that is generated as a result of both pressure gradient and applied electric field.

  • analysis of Electroosmotic Flow of power law fluids in a slit microchannel
    Journal of Colloid and Interface Science, 2008
    Co-Authors: Cunlu Zhao, Jacob H. Masliyah, Emilijk Zholkovskij, Chun Yang
    Abstract:

    Electroosmotic Flow of power-law fluids in a slit channel is analyzed. The governing equations including the linearized Poisson-Boltzmann equation, the Cauchy momentum equation, and the continuity equation are solved to seek analytical expressions for the shear stress, dynamic viscosity, and velocity distribution. Specifically, exact solutions of the velocity distributions are explicitly found for several special values of the Flow behavior index. Furthermore, with the implementation of an approximate scheme for the hyperbolic cosine function, approximate solutions of the velocity distributions are obtained. In addition, a generalized Smoluchowski velocity is introduced by taking into account contributions due to the finite thickness of the electric double layer and the Flow behavior index of power-law fluids. Calculations are performed to examine the effects of kappaH, Flow behavior index, double layer thickness, and applied electric field on the shear stress, dynamic viscosity, velocity distribution, and average velocity/Flow rate of the Electroosmotic Flow of power-law fluids.

  • Dynamic aspects of Electroosmotic Flow
    Microfluidics and Nanofluidics, 2006
    Co-Authors: Yali Zhang, Chun Yang, Teck Neng Wong, Kim Tiow Ooi
    Abstract:

    This article presents an analysis of the frequency and time dependent Electroosmotic Flow in open-end and closed-end microchannels of arbitrary cross-section shape. In the numerical model, the modified Navier–Stokes equation governing the AC Electroosmotic Flow is solved using the control volume method. The iterative approach is used to determine the induced backpressure gradient. The potential distribution of the EDL in the channel is obtained by solving the non-linear 2D Poisson–Blotzmann equation. The comparison between the control volume formulation and the Green’s function method for the case of a rectangular microchannel shows a good agreement. The time evolution of the Electroosmotic Flow and the effect of a frequency-dependent AC electric field on the oscillating Electroosmotic Flow are also examined. The effect of the induced backpressure gradient with the frequency of the applied electric field is also shown.

  • Analysis of Electroosmotic Flow in a microchannel packed with microspheres
    Microfluidics and Nanofluidics, 2005
    Co-Authors: Yuejun Kang, Chun Yang, Xiaoyang Huang
    Abstract:

    The Electroosmotic Flow in a microchannel packed with microspheres under both direct and alternating electric fields is analyzed. In the case of the steady DC electroosmosis in a packed microchannel, the so-called “capillary model” is used, in which it is assumed that a porous medium is equivalent to a series of intertwined tubules. The interstitial tubular velocity is obtained by analytically solving the Navier–Stokes equation and the complete Poisson–Boltzmann equation. Then, using the volume-averaging method, the solution for the Electroosmotic Flow in a single charged cylindrical tubule is applied to estimate the electroosmosis in the overall porous media by introducing the porosity and tortuosity. Assuming uniform porosity, an exact solution accounting for the electrokinetic wall effect is obtained by solving the modified Brinkman momentum equation. For the Electroosmotic Flow under alternating electric fields in a cylindrical microchannel packed with microspheres of uniform size, two different conditions regarding the openness of the channel ends are considered. Based on the capillary model, the time-periodic oscillating Electroosmotic Flow in an open-ended microchannel in response to the application of an alternating electric field is obtained using the Green’s function approach to the Navier–Stokes equation. When the two ends of the channel are closed, a backpressure is induced to generate a counter Flow, resulting in a new zero Flow rate. Such induced backpressure associated with the counter Flow in a closed-end microchannel is obtained analytically by solving the transient modified Brinkman momentum equation.

  • Analysis of Electroosmotic Flow in a microchannel packed with microspheres
    Microfluidics and Nanofluidics, 2005
    Co-Authors: Y.j. Kang, Chun Yang, X Y Huang
    Abstract:

    The Electroosmotic Flow in a microchannel packed with microspheres under both direct and alternating electric fields is analyzed. In the case of the steady DC electroosmosis in a packed microchannel, the so-called "capillary model" is used, in which it is assumed that a porous medium is equivalent to a series of intertwined tubules. The interstitial tubular velocity is obtained by analytically solving the Navier-Stokes equation and the complete Poisson-Boltzmann equation. Then, using the volume-averaging method, the solution for the Electroosmotic Flow in a single charged cylindrical tubule is applied to estimate the electroosmosis in the overall porous media by introducing the porosity and tortuosity. Assuming uniform porosity, an exact solution accounting for the electrokinctic wall effect is obtained by solving the modified Brinkman momentum equation. For the Electroosmotic Flow under alternating electric fields in a cylindrical microchannel packed with microspheres of uniform size, two different conditions regarding the openness of the channel ends are considered. Based on the capillary model, the time-periodic oscillating Electroosmotic Flow in an open-ended microchannel in response to the application of an alternating electric field is obtained using the Green's function approach to the Navier-Stokes equation. When the two ends of the channel are closed, a backpressure is induced to generate a counter Flow, resulting in a new zero Flow rate. Such induced backpressure associated with the counter Flow in a closed-end microchannel is obtained analytically by Solving the transient modified Brinkman momentum equation.

Shih-hsiang Chang - One of the best experts on this subject based on the ideXlab platform.

  • Unsteady Electroosmotic Flow in asymmetrically charged slit microchannel containing salt-free solution
    2010 International Symposium on Computer Communication Control and Automation (3CA), 2010
    Co-Authors: Shih-hsiang Chang
    Abstract:

    A theoretical study on the Electroosmotic Flow through a slit microchannel containing a salt-free solution is presented for dissimilar constant surface charges. Based on the exact analytical solutions for the electric potential distribution and the transient Electroosmotic Flow velocity, a systematic parametric study on the characteristics of the transient Electroosmotic Flow is investigated. The two dominant parameters affecting the transient behavior of Electroosmotic Flow are found to be the ratio of surface charges and the width of slit. In addition, it is found that the Electroosmotic Flow always moves in the same direction, irrespective of the ratio of surface charge densities, which is different from that observed in an electrolyte solution.

  • Electroosmotic Flow in slit microchannel containing salt-free solution
    European Journal of Mechanics - B Fluids, 2010
    Co-Authors: Shih-hsiang Chang
    Abstract:

    A theoretical study on the Electroosmotic Flow through a uniformly charged planar slit microchannel containing a salt-free solution is presented. Based on the exact analytical solutions for the electric potential distribution and the transient Electroosmotic Flow velocity, a systematic parametric study on the characteristics of the transient Electroosmotic Flow is then investigated. The results show that the general behavior of Electroosmotic Flow in a planar slit is similar to that in a cylindrical capillary; however, the characteristic time to reach the steady-state Flow, the Electroosmotic mobility and the correction factor to the Smoluchowski equation in a slit are larger than those in a cylinder with its diameter equal to the slit width. Furthermore, the osmotic pressure of counterion between two equally charged planar surfaces immersed in a salt-free solution is found to be always repulsive. In addition, the implications of these results on electroosmosis in a microchannel are discussed.

  • Analysis of Unsteady Electroosmotic Flow in Dissimilarly Charged Slit Surfaces Containing Salt-Free Medium
    2009
    Co-Authors: Shih-hsiang Chang
    Abstract:

    A theoretical study on the Electroosmotic Flow through a slit microchannel containing a salt-free medium is presented for dissimilar constant surface charges. 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 investigated. The two dominant parameters affecting the transient behavior of Electroosmotic Flow are found to be the ratio of surface charges and the width of slit. Moreover, the Debye length has no effect on the transient response of Electroosmotic Flow. In addition, it is found that the Electroosmotic Flow always moves in the same direction, irrespective of the ratio of surface charge densities, which is different from that observed in an electrolyte solution.

  • Transient Electroosmotic Flow in Slit Microchannel Containing Salt-Free Medium
    ASME 2009 7th International Conference on Nanochannels Microchannels and Minichannels, 2009
    Co-Authors: Shih-hsiang Chang
    Abstract:

    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.Copyright © 2009 by ASME

H Q Gong - One of the best experts on this subject based on the ideXlab platform.

  • numerical analysis of the thermal effect on Electroosmotic Flow and electrokinetic mass transport in microchannels
    Analytica Chimica Acta, 2004
    Co-Authors: Gongyue Tang, Chun Yang, Cheekiong Chai, H Q Gong
    Abstract:

    Abstract Joule heating is present in electrokinetically driven Flow and mass transport in microfluidic systems. Nowadays, there is a trend of replacing costly glass-based microfluidic systems by the disposable, cheap polymer-based microfluidic systems. Due to poor thermal conductivity of polymer materials, the thermal management of the polymer-based microfluidic systems may become a problem. In this study, numerical analysis is presented for transient temperature development due to Joule heating and its effect on the Electroosmotic Flow (EOF) and mass species transport in microchannels. The proposed model includes the coupling Poisson–Boltzmann (P–B) equation, the modified Navier–Stokes (N–S) equations, the conjugate energy equation, and the mass species transport equation. The results show that the time development for both the Electroosmotic Flow field and the Joule heating induced temperature field are less than 1 s. The Joule heating induced temperature field is strongly dependent on channel size, electrolyte concentration, and applied electric field strength. The simulations reveal that the presence of the Joule heating can result in significantly different characteristics of the Electroosmotic Flow and electrokinetic mass transport in microchannels.

  • joule heating effect on Electroosmotic Flow and mass species transport in a microcapillary
    International Journal of Heat and Mass Transfer, 2004
    Co-Authors: Gongyue Tang, J C Chai, Chun Yang, H Q Gong
    Abstract:

    This study presents a numerical analysis of Joule heating effect on the Electroosmotic Flow and mass species transport, which has a direct application in the capillary electrophoresis based BioChip technology. A rigorous mathematic model for describing the Joule heating in an Electroosmotic Flow including the Poisson–Boltzmann equation, the modified Navier–Stokes equations and the energy equation is developed. All these equations are coupled through the temperature-dependent liquid dielectric constant, viscosity, and thermal conductivity. By numerically solving the aforementioned equations simultaneously, the double layer potential profile, the Electroosmotic Flow field, and the temperature distribution in a cylindrical microcapillary are computed. A systematic study is carried out to evaluate the Joule heating and its effects under the influences of the capillary radius, the buffer solution concentration, the applied electric field strength, and the heat transfer coefficient. In addition, the Joule heating effect on sample species transport in a microcapillary is also investigated by numerically solving the mass transfer equation with consideration of temperature-dependent diffusion coefficient and electrophoresis mobility. The simulations reveal that the presence of the Joule heating could have a great impact on the Electroosmotic Flow and mass species transport.

  • Numerical Simulation of Joule Heating Effect on Electroosmotic Flow and Electrokinetic Mass Transport in Microchannels
    Volume 3, 2004
    Co-Authors: Gongyue Tang, Chun Yang, Cheekiong Chai, H Q Gong
    Abstract:

    This study presents a numerical simulation of Joule heating effect on Electroosmotic Flow and mass species transport in microchannels, which has direct applications in the capillary electrophoresis based Biochip technology. The proposed model includes the Poisson-Boltzmann equation, the modified Navier-Stokes equations, the conjugate energy equation, and the mass species transport equation. The numerical predictions show that the time development for both the Electroosmotic Flow field and the Joule heating induced temperature field are less than 1 second. The Joule heating induced temperature field is strongly dependent on channel size, electrolyte concentration, and applied electric field strength. The simulations reveal that the presence of Joule heating can result in significantly different characteristics of the Electroosmotic Flow and electrokinetic mass transport in microchannels.

  • Joule Heating Induced Thermal and Hydrodynamic Development in Microfluidic Electroosmotic Flow
    ASME 2nd International Conference on Microchannels and Minichannels, 2004
    Co-Authors: Gongyue Tang, Chun Yang, C. J. Chai, H Q Gong
    Abstract:

    Joule heating is present in electrokinetically driven Flow and mass transport in microfluidic systems. Specifically, in the cases of high applied voltages and concentrated buffer solutions, the thermal management may become a problem. In this study, a mathematical model is developed to describe the Joule heating and its effects on Electroosmotic Flow and mass species transport in microchannels. The proposed model includes the Poisson equation, the modified Navier-Stokes equation, and the conjugate energy equation (for the liquid solution and the capillary wall). Specifically, the ionic concentration distributions are modeled using (i) the general Nernst-Planck equation, and (ii) the simple Boltzmann distribution. These governing equations are coupled through temperature-dependent phenomenological thermal-physical coefficients, and hence they are numerically solved using a finite-volume based CFD technique. A comparison has been made for the results of the ionic concentration distributions and the Electroosmotic Flow velocity and temperature fields obtained from the Nernst-Planck equation and the Boltzmann equation. The time and spatial developments for both the Electroosmotic Flow fields and the Joule heating induced temperature fields are presented. In addition, sample species concentration is obtained by numerically solving the mass transport equation, taking into account of the temperature-dependent mass diffusivity and electrophoresis mobility. The results show that the presence of the Joule heating can result in significantly different electroosomotic Flow and mass species transport characteristics.Copyright © 2004 by ASME

  • Electroosmotic Flow and Mass Species Transport in a Microcapillary Under Influences of Joule Heating
    Volume 2: Symposia Parts A B and C, 2003
    Co-Authors: Gongyue Tang, Chun Yang, Cheekiong Chai, H Q Gong
    Abstract:

    This study presents a numerical analysis of Joule heating effect on the Electroosmotic Flow and species transport, which has a direct application in the capillary electrophoresis based BioChip technology. A rigorous mathematic model for describing the Joule heating in an Electroosmotic Flow including Poisson-Boltzmann equation, modified Navier-Stokers equations and energy equation is developed. All these equations are coupled together through the temperature-dependent parameters. By numerically solving aforementioned equations simultaneously, the Electroosmotic Flow field and the temperature distributions in a cylindrical microcapillary are obtained. A systematic study is carried out under influences of different geometry sizes, buffer solution concentrations, applied electric field strengths, and heat transfer coefficients. In addition, sample species transport in a microcapillary is also investigated by numerically solving the mass transfer equation with consideration of temperature-dependant diffusion coefficient and electrophoresis mobility. The characteristics of the Joule heating, Electroosmotic Flow, and sample species transport in microcapillaries are discussed. The simulations reveal that the presence of the Joule heating could have a great impact on the Electroosmotic Flow and sample species transport.Copyright © 2003 by ASME

Cha'o-kuang Chen - One of the best experts on this subject based on the ideXlab platform.

  • Characteristics of combined Electroosmotic Flow and pressure-driven Flow in microchannels with complex-wavy surfaces
    International Journal of Thermal Sciences, 2012
    Co-Authors: Ching Chang Cho, Chieh-li Chen, Cha'o-kuang Chen
    Abstract:

    Abstract A numerical investigation is performed into the Flow characteristics of various electrokinetic and pressure-driven Flows within microchannels with complex-wavy surfaces. Four different Flows are considered, including (1) pure Electroosmotic Flow; (2) pure pressure-driven Flow; (3) combined Electroosmotic/pressure-driven Flow with a favorable pressure gradient; and (4) combined Electroosmotic/pressure-driven Flow with an adverse pressure gradient. The effects of the wavy surface geometry parameters and the ratio of the Electroosmotic Flow velocity to the pressure-driven Flow velocity on the fluid Flow characteristics are examined. The results show that while Flow recirculations are induced by pure pressure-driven Flow, recirculation structures are not formed in pure Electroosmotic Flow. In addition, it is shown that electrokinetically induced velocity is more sensitive than pressure-induced velocity to the waveform geometry. For combined Electroosmotic/pressure-driven Flow with a favorable pressure gradient, the momentum of the combined Flow is sufficient to prevent the formation of Flow recirculations. However, for combined Electroosmotic/pressure-driven Flow with an adverse pressure gradient, Flow recirculations are induced near the wave crest when the ratio of the Electroosmotic Flow velocity to the pressure-driven Flow velocity falls below a certain threshold value. It is observed that the recirculation structures are longer and thinner than those that are generated near the wave trough under pure pressure-driven Flow conditions. The heat transfer characteristics for various Flow scenarios are also investigated in the complex-wavy surface microchannel with constant surface temperature conditions by considering the Joule heating effect. The results show that the thermal entrance length significantly depends on the ratio of the Electroosmotic Flow velocity to the pressure-driven Flow velocity. The longest entrance length is presented in the Flow scenario of the favorable pressure gradient combined Flow. In a thermally fully developed region, the heat transfer performance is dependent on the magnitude of the Joule heating and the geometry structure and is independent of Flow scenarios.

  • A NUMERICAL INVESTIGATION INTO Electroosmotic Flow IN MICROCHANNELS WITH COMPLEX WAVY SURFACES
    Thermal Science, 2011
    Co-Authors: Her-terng Yau, Ching Chang Cho, Cheng-chi Wang, Cha'o-kuang Chen
    Abstract:

    This study investigates the Flow characteristics of Electroosmotic Flow in a microchannel with complex wavy surfaces. A general method of coordinate transformation is used to solve the governing equations describing the Electroosmotic Flow in the microchannel. Numerical simulations are performed to analyze the effects of wave amplitude on the electrical field, Flow streamlines, and Flow fields in the microchannel. The simulation results show that, compared to a traditional pressure-driven Flow, Flow recirculation is not developed in the Electroosmotic Flow in a microchannel with complex wavy surfaces. The simulations also show that the electrical field and velocity profiles change along the channel in the region of wavy surfaces. Non-flat velocity profiles are observed in different cross-sections of the channel in the region of wavy surfaces.

Vincent Chan - One of the best experts on this subject based on the ideXlab platform.