Numerical Simulation on Transient Electrophoretic Motion of a Circular Particle in a T-Shaped Slit Microchannel

2003 ◽  
Author(s):  
Chunzhen Ye ◽  
Dongqing Li
Keyword(s):  
Numerical Simulation ◽  
Liquid Phase ◽  
Flow Field ◽  
Electric Field ◽  
Particle Motion ◽  
Outer Region ◽  
Double Layers ◽  
Circular Particle ◽  
Electric Potentials ◽  
Inner Region

This paper considers the electrophoretic motion of a circular particle in a T-shaped slit microchannel, where the size of the channel is close to that of the particle. During the process, the electric field (i.e., the gradient of the electric potential) changes with the particle motion, which in return influences the flow field and the particle motion. Therefore, the electric field, the flow field and the particle motion are coupled together, and this is an unsteady process. The objective is to obtain a fundamental understanding of the characteristics of the particle motion in the complicated T-shaped junction region. Such influences on the electric field and the particle motion are investigated as the applied electric potentials, the geometry of the channel and the size of the particle. In the theoretical analysis, the liquid phase is divided into the inner region and the outer region. The inner region consists of the electrical double layers and the outer region consists of the remainder of the liquid. Under the assumption of thin electrical double layer, a mathematical model governing the inner region, the outer region and the particle motion is developed. A direct numerical simulation method using the finite element method is employed. In this method, a continuous hydrodynamic model is adopted. By this model, both the liquid phase in the outer region and the particle phase are governed by the same momentum equations. ALE method is used to track the surface of the particle at each time step. The numerical results show that the electric field is influenced by the applied electric potentials, the geometry of the channel and the particle suspension, and that the particle motion is mainly dominated by the local electric field. It is also found that the magnitude of the particle motion is dependent on its own size in the same channel.

Numerical Simulation on the Electrophoretic Motion of Multiple Particles in Microchannels

2004 ◽  
Author(s):  
Chunzhen Ye ◽  
Dongqing Li
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Electric Field ◽  
Particle Motion ◽  
Outer Region ◽  
Numerical Results ◽  
The Other ◽  
Double Layers ◽  
Rectangular Microchannel ◽  
Moving Particle

This paper considers the electrophoretic motion of multiple spheres in an aqueous electrolyte solution in a straight rectangular microchannel, where the size of the channel is close to that of the particles. This is a complicated 3-D transient process where the electric field, the flow field and the particle motion are coupled together. The objective is to numerically investigate how one particle influences the electric field and the flow field surrounding the other particle and the particle moving velocity. It is also aimed to investigate and demonstrate that the effects of particle size and electrokinetic properties on particle moving velocity. Under the assumption of thin electrical double layers, the electroosmotic flow velocity is used to describe the flow in the inner region. The model governing the electric field and the flow field in the outer region and the particle motion is developed. A direct numerical simulation method using the finite element method is adopted to solve the model. The numerical results show that the presence of one particle influences the electric field and the flow field adjacent to the other particle and the particle motion, and that this influences weaken when the separation distance becomes bigger. The particle motion is dependent on its size, with the smaller particle moving a little faster. In addition, the zeta potential of particle has an effective influence on the particle motion. For a faster particle moving from behind a slower one, numerical results show that the faster moving particle will climb and then pass the slower moving particle then two particles’ centers are not located on a line parallel to the electric field.

scholarly journals Experimental and CFD Studies of the Hydrodynamics in Wet Agglomeration Process

2018 ◽  
Vol 2 (3) ◽  
pp. 32 ◽  
Author(s):  
Benjamin Oyegbile ◽  
Guven Akdogan ◽  
Mohsen Karimi
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Flow Analysis ◽  
Outer Region ◽  
Tangential Velocity ◽  
Numerical Code ◽  
Cfd Model ◽  
Rotating Disc ◽  
Batch Mode ◽  
Agglomeration Process

In this study, an experimentally validated computational model was developed to investigate the hydrodynamics in a rotor-stator vortex agglomeration reactor RVR having a rotating disc at the centre with two shrouded outer plates. A numerical simulation was performed using a simplified form of the reactor geometry to compute the 3-D flow field in batch mode operations. Thereafter, the model was validated using data from a 2-D Particle Image Velocimetry (PIV) flow analysis performed during the design of the reactor. Using different operating speeds, namely 70, 90, 110, and 130 rpm, the flow fields were computed numerically, followed by a comprehensive data analysis. The simulation results showed separated boundary layers on the rotating disc and the stator. The flow field within the reactor was characterized by a rotational plane circular forced vortex flow, in which the streamlines are concentric circles with a rotational vortex. Overall, the results of the numerical simulation demonstrated a fairly good agreement between the Computational Fluid Dynamics (CFD) model and the experimental data, as well as the available theoretical predictions. The swirl ratio β was found to be approximately 0.4044, 0.4038, 0.4044, and 0.4043 for the operating speeds of N = 70, 90, 110, and 130 rpm, respectively. In terms of the spatial distribution, the turbulence intensity and kinetic energy were concentrated on the outer region of the reactor, while the circumferential velocity showed a decreasing intensity towards the shroud. However, a comparison of the CFD and experimental predictions of the tangential velocity and the vorticity amplitude profiles showed that these parameters were under-predicted by the experimental analysis, which could be attributed to some of the experimental limitations rather than the robustness of the CFD model or numerical code.

Characterization of interactive force acting on colloidal particles near an electrode in presence of a high-frequency (>10 kHz) AC electric field using particle diffusometry

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Kshitiz Gupta ◽  
Dong Hoon Lee ◽  
Steven T. Wereley ◽  
Stuart J. Williams
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Particle Motion ◽  
Electrode Surface ◽  
High Frequency ◽  
Colloidal Particles ◽  
Low Frequency ◽  
Double Layers ◽  
Average Height ◽  
Ac Electric Field

Colloidal particles like polystyrene beads and metallic micro and nanoparticles are known to assemble in crystal-like structures near an electrode surface under both DC and AC electric fields. Various studies have shown that this self-assembly is governed by a balance between an attractive electrohydrodynamic (EHD) force and an induced dipole-dipole repulsion (Trau et al., 1997). The EHD force originates from electrolyte flow caused by interaction between the electric field and the polarized double layers of both the particles and the electrode surface. The particles are found to either aggregate or repel from each other on application of electric field depending on the mobility of the ions in the electrolyte (Woehl et al., 2014). The particle motion in the electrode plane is studied well under various conditions however, not as many references are available in the literature that discuss the effects of the AC electric field on their out-of-plane motion, especially at high frequencies (>10 kHz). Haughey and Earnshaw (1998), and Fagan et al. (2005) have studied the particle motion perpendicular to the electrode plane and their average height from the electrode mostly in presence of DC or low frequency AC (<1 kHz) electric field. However, these studies do not provide enough insight towards the effects of high frequency (>10 kHz) electric field on the particles’ motion perpendicular to the electrode plane.  

scholarly journals Phase-Averaged Method Applied to Periodic Flow Between Shrouded Corotating Disks

2003 ◽  
Vol 9 (4) ◽  
pp. 293-301 ◽  
Author(s):  
Shen-Chun Wu ◽  
Yau-Ming Chen
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Dynamic Behavior ◽  
Outer Region ◽  
Experimental Results ◽  
Periodic Flow ◽  
Vortical Structures ◽  
Boundary Layer Region ◽  
Layer Region ◽  
Inner Region

This study investigates the coherent flow fields between corotating disks in a cylindrical enclosure. By using two laser velocimeters and a phase-averaged technique, the vortical structures of the flow could be reconstructed and their dynamic behavior was observed. The experimental results reveal clearly that the flow field between the disks is composed of three distinct regions: an inner region near the hub, an outer region, and a shroud boundary layer region. The outer region is distinguished by the presence of large vortical structures. The number of vortical structures corresponds to the normalized frequency of the flow.

Driven, dissipative, energy-conserving magnetohydrodynamic equilibria. Part 2. The screw pinch

1993 ◽  
Vol 49 (1) ◽  
pp. 125-159 ◽  
Author(s):  
Michael L. Goodman
Keyword(s):  
Thermal Conductivity ◽  
Electric Field ◽  
Boundary Conditions ◽  
Transition Region ◽  
Outer Region ◽  
Radial Electric Field ◽  
Axial Current ◽  
Number Density ◽  
Energy Conserving ◽  
Inner Region

A cylindrically symmetric, electrically driven, dissipative, energy-conserving magnetohydrodynamic equilibrium model is considered. The high-magneticfield Braginskii ion thermal conductivity perpendicular to the local magnetic field and the complete electron resistivity tensor are included in an energy equation and in Ohm's law. The expressions for the resistivity tensor and thermal conductivity depend on number density, temperature, and the poloidal and axial (z-component) magnetic field, which are functions of radius that are obtained as part of the equilibrium solution. The model has plasma-confining solutions, by which is meant solutions characterized by the separation of the plasma into two concentric regions separated by a transition region that is an internal boundary layer. The inner region is the region of confined plasma, and the outer region is the region of unconfined plasma. The inner region has average values of temperature, pressure, and axial and poloidal current densities that are orders of magnitude larger than in the outer region. The temperature, axial current density and pressure gradient vary rapidly by orders of magnitude in the transition region. The number density, thermal conductivity and Dreicer electric field have a global minimum in the transition region, while the Hall resistivity, Alfvén speed, normalized charge separation, Debye length, (ωλ)ion and the radial electric field have global maxima in the transition region. As a result of the Hall and electron-pressure-gradient effects, the transition region is an electric dipole layer in which the normalized charge separation is localized and in which the radial electric field can be large. The model has an intrinsic value of β, about 13·3%, which must be exceeded in order that a plasma-confining solution exist. The model has an intrinsic length scale that, for plasma-confining solutions, is a measure of the thickness of the boundary-layer transition region. If appropriate boundary conditions are given at R = 0 then the equilibrium is uniquely determined. If appropriate boundary conditions are given at any outer boundary R = a then the equilibrium exhibits a bifurcation into two states, one of which exhibits plasma confinement and carries a larger axial current than the other, which is almost homogeneous and cannot confine a plasma. Exact expressions for the two values of the axial current in the bifurcation are derived. If the boundary conditions are given at R = a then a solution exists if and only if the constant driving electric field exceeds a critical value. An exact expression for this critical electric field is derived. It is conjectured that the bifurcation is associated with an electric-field-driven transition in a real plasma, between states with different rotation rates, energy dissipation rates and confinement properties. Such a transition may serve as a relatively simple example of the L—H mode transition observed in tokamaks.

scholarly journals The root of a comet tail: Rosetta ion observations at comet 67P/Churyumov–Gerasimenko

2018 ◽  
Vol 616 ◽  
pp. A21 ◽  
Author(s):  
E. Behar ◽  
H. Nilsson ◽  
P. Henri ◽  
L. Berčič ◽  
G. Nicolaou ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Electric Field ◽  
Outer Region ◽  
Field Measurements ◽  
Night Side ◽  
Combined Action ◽  
Single Night ◽  
Inner Region ◽  
Comet 67P

Context. The first 1000 km of the ion tail of comet 67P/Churyumov–Gerasimenko were explored by the European Rosetta spacecraft, 2.7 au away from the Sun. Aims. We characterised the dynamics of both the solar wind and the cometary ions on the night-side of the comet’s atmosphere. Methods. We analysed in situ ion and magnetic field measurements and compared the data to a semi-analytical model. Results. The cometary ions are observed flowing close to radially away from the nucleus during the entire excursion. The solar wind is deflected by its interaction with the new-born cometary ions. Two concentric regions appear, an inner region dominated by the expanding cometary ions and an outer region dominated by the solar wind particles. Conclusions. The single night-side excursion operated by Rosetta revealed that the near radial flow of the cometary ions can be explained by the combined action of three different electric field components, resulting from the ion motion, the electron pressure gradients, and the magnetic field draping. The observed solar wind deflection is governed mostly by the motional electric field −uion × B.

scholarly journals Experimental Study and Hydrodynamic Modelling of the Wet Agglomeration Process

2018 ◽  
Author(s):  
Benjamin Oyegbile ◽  
Guven Akdogan ◽  
Mohsen Karimi
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Flow Analysis ◽  
Outer Region ◽  
Tangential Velocity ◽  
Numerical Code ◽  
Cfd Model ◽  
Rotating Disc ◽  
Batch Mode ◽  
Agglomeration Process

In this study, an experimentally validated computational model was developed to investigate the hydrodynamics in a rotor-stator vortex RVR agglomeration reactor having a rotating disc at the centre with two shrouded outer plates. A numerical simulation was performed using a simplified form of the reactor geometry to compute the 3D flow field in batch mode operations. Thereafter, the model was validated using data from a 2D Particle Image Velocimetry (PIV) flow analysis performed during the design of the reactor. Using different operating speeds&mdash;70, 90, 110 and 130 rpm, the flow fields were computed numerically followed by a comprehensive data analysis. The simulation results showed separated boundary layers on the rotating disc and the stator. The flow field within the reactor is characterized by a rotational plane circular forced vortex flow in which the streamlines are concentric circles with a rotational vortex. Overall, the results of the numerical simulation demonstrate a fairly good agreement between the CFD model and the experimental data as well as the available theoretical predictions. The swirl ratio &beta; was found to be approximately 0.4044, 0.4038, 0.4044 and 0.4043 for operating speeds of N=70, 90, 110 and 130 rpm respectively. In terms of the spatial distribution, the turbulence intensity and kinetic energy are concentrated on the outer region of the reactor while the axial velocity showed a decreasing intensity towards the shroud. However, a comparison of the CFD and experimental predictions of the tangential velocity and the vorticity amplitude profiles shows that these parameters were under-predicted by the experimental analysis which could be attributed to some of the experimental limitations rather than the robustness of the CFD model or numerical code.

Electrophoretic Motion of Particles in a Microsystem

2006 ◽  
Author(s):  
Y. F. Yap ◽  
J. C. Chai ◽  
T. N. Wong ◽  
N. T. Nguyen ◽  
K. C. Toh ◽  
...  
Keyword(s):  
Charged Particle ◽  
Flow Field ◽  
Electric Field ◽  
Numerical Models ◽  
Body Motion ◽  
Navier Stokes ◽  
Inorganic Particles ◽  
Slip Boundary ◽  
Circular Particle ◽  
Positively Charged

Electrophoresis is the motion of a charged particle relative to the surrounding liquid due to an imposed external electric field1. Its applications include but are not limited to characterization and manipulation of organic and inorganic particles. In particular, electrophoresis has been applied to a variety of analytical separation problems involving nucleic acids, proteins and drugs. For electrophoresis on various Lab-on-a-chip platforms, the particles are of sizes comparable to the microchannel in which they flow. As such, particle-particle and particle-wall interactions are no longer negligible. Therefore, the electric field, the flow field and the particles motion are strongly coupled together. Numerical models based on a moving-grid method2 have been employed to investigate the related phenomena. Mesh regeneration as the particles move is an extra computational complication. To circumvent the complexity of mesh regeneration, a level-set based fixed-grid method3 is presented for electrophoretic motion of particles in this article. The particles are assumed to be a highly viscous liquid constraint to move with rigid body motion. A distance function is employed to represent the liquid-particle interfaces. The electric field, the flow field and the particles motion are governed respectively by the Poisson, the Navier-Stokes and the Euler-Newton equations. The effect of the electric field on the particle motion is accounted for by incorporating slip boundary conditions on the particles surfaces. The nonlinear governing equations are discretized and solved using a finite volume method4. The model is used to investigate electrophoretic motion of non-conducting circular and elliptical particles in a microsystem. Figure 1 shows the electrophoretic motion of a single circular particle in a microchannel. The induced electroosmotic flow is from the left to the right. The thick circles are the particle at t = 0. The direction of the particle movement is indicated by the arrows. The motions of the particle if neutral, positively or negatively charged are obviously different. Basically, a positively charged particle move faster than the main flow. However, a negatively charged particle flows slower. When the particle is highly charged negative, it can even flow against the streamwise direction toward upstream (+V) as in Fig. 1c. This suggests that there would be a situation where the particle can be kept static. Figure 2 shows the electrophoretic motion of multiple particles. The initial locations of the particles are shown in Fig. 2a. In the case of charged particles, particle 1, 2 and 3 are respectively negatively, neutral and positively charged. Particle 1 which is elliptical undergoes obvious rotational motion when charged (Fig. 2c). The case of the neutral particles (Fig. 2b) is included for comparison.

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