EHD Flow Research Articles

Nanoantennas report dissipative assembly in oscillatory electric fields

Understanding driving forces for dissipative, i.e., out of equilibrium, assembly of nanoparticles from colloidal solution at liquid–solid interfaces provides the ability to design external cues for reconfigurable device response. Here electrohydrodynamic flow (EHD) at an electrode-liquid interface is investigated as a dissipative driving force for tuning optical response. EHD results from an oscillatory electric field in a liquid cell between two electrodes and drives assembly of gold nanoparticles (NP) into two-dimensional clusters on electrode surfaces. Clusters are chemically crosslinked during assembly to freeze assemblies for electron microscopy characterization in order to understand how to ‘nucleate’ cluster formation. Electron microscopy images show deposition with a potential having an amplitude of 5 V and frequency of 100 Hz produces surfaces with isolated NP, which can seed EHD flow. A second deposition step at 5 V and 500 Hz produces a high density of quadramers on surfaces. When exciting near the local surface plasmon resonance of the Au NP clusters formed during assembly, Au NPs serve as in situ nanoantenna reporters of assembly and disassembly. Surface enhanced Raman scattering (SERS) measurements of Au NP capped with 4-mercaptobenzoic acid show order of magnitude signal enhancements occur during cluster formation in the presence of an oscillatory field, which occurs on a time scale of seconds. Confocal fluorescence spectroscopy is used to monitor the dissipative assembly of Au NP over multiple cycles. Results provide insight on how electrical stimuli and seeding local perturbations affects formation of NP clusters and resultant optical response provides insight on how to tune response of optically active surfaces.

Study of the Electrical Conductivity and EHD Flows of Weakly Concentrated Solution of Transformer Oil with an Electron-Acceptor Impurity (Iodine)

Study of the Electrical Conductivity and EHD Flows of Weakly Concentrated Solution of Transformer Oil with an Electron-Acceptor Impurity (Iodine)

Modal analysis of EHD jets through the SVD-based POD technique

An EHD flow has complex characteristics with superimposed characteristic structures of various scales due to the coupling effect of the electric and flow fields. This paper provides a new research perspective on active control techniques of EHD flows by unraveling the large-scale dynamic structure of the dominant electroconvection from the manifold of the jet. The SVD-based POD technique in our work marks the first comprehensive investigation of modal analysis for EHD jets, aiming at extracting reduced-order modes that capture the main features and exploring the mechanisms that govern these jets through a deeper understanding of dynamic physics. The findings indicate that large-scale coherent structures that determine the EHD flows regularly emerge in the low-order modes, and fine-scale vortex structures typically appear in the high-order modes. In addition, the POD-based flow field recovery technique can effectively remove the spurious vectors from the PIV dataset by simply excluding the high-order modes from the expansion during reconstruction.

Research of the effect of different corrugated dust collection plates on particle removal in electrostatic precipitators

In this paper, a multi-physics field coupled model of electric, flow and particle fields was constructed by COMSOL to compare the effects of three different corrugated dust collector plates on electric field distribution, airflow field, particle trajectories and dust removal efficiency in an electrostatic precipitator, and to compare them with a conventional electrostatic precipitator with a parallel plate structure. The results indicated that the corrugated dust collection plate influenced the electric field within the ESP channel, while the wire plate spacing directly affected the size and distribution of space charge density. Furthermore, the corrugated dust collection plate also affected the EHD flow within the channel, with the D2-ESP and D3-ESP being the most strongly influenced by the ionic wind. By comparing the dust removal efficiency of the four ESPs, we found that D2-ESP has the highest dust removal efficiency, followed by D3-ESP, then Flat-ESP, and finally D1-ESP. The ranking order of the four ESPs' dust removal efficiency is consistent with the ranking order of the space charge density within the four ESP channels, which shows that the size of the space charge density directly affects the dust removal efficiency of ESPs. Numerical simulation results show that the change of wire plate spacing is the main reason why corrugated ESP affects the dust removal efficiency of electrostatic precipitators.

EHD flow auxiliary particle collection in HVDC electrostatic precipitator based on PIV flow visualization technology

The electrostatic precipitator (ESP) is modified with the aid of an EHD flow in high voltage direct current (HVDC) to trap submicron-sized and ultra-high resistivity particles. In this study, the modified method for micron spherical silica was developed and optimized by particle image velocimetry (PIV) and numerical simulation. Meanwhile, scattering images of particle movement were obtained by laser and CCD camera. These results showed that the fine particles were driven by EHD flow towards the cavity. The D50 and D90 of particles measured by using the SYNC-type particle size analyzer inside the auxiliary dust removal cavity were 0.635 μm and 1.178 μm, which were much smaller than those of the particles deposited on the rear side of the cavity. The particle morphology was observed by scanning electron microscope (SEM), which indicated that multi-layer particles were agglomerating on the surface of the plate electrodes. However, particles were distributed in loose mono-layer in the cavity with no obvious agglomeration. The results showed that the modified method improved the efficiency.

An Electrohydrodynamic analysis for the characterisation of fluid flow within conducting and non-conducting channels

This paper presents a generalized non-dimensional theoretical formulation with boundary conditions to analyze the EHD flow within the conducting and non-conducting channels. The substantial effect of normal and tangential components of electric field on fluid flow within the channel is presented through simulation results based on the non-dimensional parameters of strength, penetration, and repulsion of electric forces. The simulation results reveal that the normal component of induced electric field transits the flow regime within surfaces of a channel. The tangential component of applied electric field increases the thickness of viscous boundary layer, leading to skewed velocity profiles.

Dynamics of liquid mass transfer in a water bridge

The paper presents experimental results of the dynamics of mass transfer through a water bridge arising between two dielectric cups with distilled water under the action of a constant high voltage between cylindrical electrodes. It is established that, depending on the ratio of the electrode diameters, the total fluid flow in the water bridge can be directed both to the cathode and to the anode. It is shown that the inversion of the direction of mass transfer of liquid through the bridge is due to the redistribution of volume charges. Keywords: water bridge, EHD flow, anode, cathode.

On the evaporation enhancement from saline water due to corona discharge generated EHD flow: A numerical and experimental study

In this paper, augmentation of water evaporation from saline water due to corona discharge generated EHD flow is numerically and experimentally examined. The effects of applied voltage and relative humidity of ambient air are considered. Relative humidity of ambient air affects both the corona discharge and the driving force of interfacial evaporation. Solution of governing equations is carried out by employing the finite volume method in OpenFOAM. Results show that for a voltage of 12 kV, evaporation in an ambient air with relative humidity of 90% could be enhanced by 600%. For a voltage of 6 kV and an ambient relative humidity of 30%, a coefficient of performance of 324 is calculated for the EHD system, meaning that the enthalpy change due to mass transfer is much larger than electric energy consumption.

Enhancement of air purification by unique W-plate structure in two-stage electrostatic precipitator: A novel design for efficient capture of fine particles

In this paper, a novel W-plate two-stage ESP was developed and investigated systematically through the experimental and simulated process. Numerical models and available calculation procedure of solving coupling electrostatic field, fluid field, and particle dynamics were established, whose accuracy was validated by experiments. The relationship among collection efficiency, gas velocity, and particle diameter was studied, and the distribution of electrostatic field, the evolution of EHD flow and fluid field, and particle dynamics, including particle charging, particle trajectory, transverse velocity, and particle concentration, were also investigated thoroughly. Results showed that W-plate two-stage ESP exhibited excellent number-based collection efficiency for fine particles which benefited from the reasonable structure design and the exceeding weak influence of EHD flow. Besides, the particle charging process suggested that the diameter decided the dominant charging mechanism, and the trajectory also played an important role in controlling the charging action. Compared with the behavior of each particle injected at different inlet positions, fine particles injected near the discharge wire got more charging number and quicker capture. Importantly, W-plate structure could exert its crucial role in capturing particles with the help of fluid field and inertial effect when inlet gas velocity increased rapidly. W-plate two-stage ESP had more than 90% number-based collection efficiency for >3 μm diameter particles and more than 75% number-based collection efficiency for 0.3–1 μm diameter submicron particles at 2 m/s gas velocity in both experimental and simulated investigations.

Структура электрогидродинамических течений инжекционного типа в переменном поле

The article presents the results of the study of the structure of electrohydrodynamic flows under an alternating electric field. The study is based on the results of computer simulation of EHD flows in the needle-plane electrode system. The characteristic frequency range of the supply sinusoidal voltage with an amplitude of 5 kV is considered. A description of the changes in the charge and velocity structure of EHD flows is carried out, characteristic features depending on the frequency of changes in the supply voltage are revealed. The periodicity of this type of EHD flows is shown.

Effect of the Vortex Formed by the Electrohydrodynamic Flow on the Motion of Particles in a Needle-plate Electrostatic Precipitator

ABSTRACT In this work, the effect of electrodynamic flow (EHD) on particle motion behavior is studied numerically on the basis of the single needle–plate electrode configuration. The interaction between primary–secondary flow and the trajectory of particles in a 3D environment is presented. In addition, the effects of the needle-shaped discharge electrode structure on the electric field and the flow field distribution are explored. Results show that the sharp surface of the needle tip causes high-intensity discharge that creates high-speed ion wind near this tip. The maximum velocity of the ionic wind can reach 9.028 m/s at applied voltage and inlet velocity of −60 kV and 1 m/s, respectively. This high-speed ion wind generated near the needle tip can increase the migration speed of particle. Moreover, the phenomenon that 90% of 1 µm particles penetrate the outlet surface indicates that the EHD flow negatively affects the capture of fine particles. The relationship among the injection position, residence time, and escape velocity of the particles further confirms that secondary flow seriously affects fine-particle capture. These results can help improve and optimize an electrode structure that reasonably uses high-speed ion wind to capture particles and prevent fine particles from escaping.

Multifield modeling of particle dynamics in an electrostatic precipitator equipped with pointed-end arista on corona

Electrostatic precipitator (ESP) is widely applied in dust removal of fine particulates. An multi-field coupling model of ESP is summed up, which equipped with pointed-end arista on corona. First, a computation work is carried out prior to compare the separation performance of two kinds of electrodes, and the result obviously shows that arista electrode performs better. Then, the adopted corona is installed in a honeycomb test section for measurement. Influences of EHD flow, supply voltage, gas velocity and particle diameter upon separation efficiency are investigated in detail both in computation and measurement. The result implies that separation increase linearly with enhancing supply voltage ranges from 10 kV to 50 kV and particle diameter ranges from 1 μm to 5 μm. When particle diameter is larger than 5 μm, separation efficiency is up to nearly 100% and barely affected. EHD flow has an significant positive influence on particle motion for particulates smaller than 5 μm in low gas velocity. Whereas separation efficiency drops with the rising gas velocity.

CVFEM approach for EHD flow of nanofluid through porous medium within a wavy chamber under the impacts of radiation and moving walls

In current investigation, ferrofluid circulation and energy transport inside a wavy-walled porous enclosure are modeled considering radiation and EHD effects. The finite volume method is employing for simulation of EHD circulation structures and thermal transmission. Properties of working fluid depend on the electric field and nanosized solid particles concentration. Impacts of thermal radiation, nanoparticles shape, and volume fraction are considered in governing equations. Distributions of unknown functions are received for various voltage, permeability, radiation parameters, nanoparticles’ shape and concentration. Results have shown that platelet form leads to the strongest convective circulation. An amplification of electric force characterizes a diminution of the boundary layer thickness. Greater permeability of the porous medium characterizes the strongest convective circulation and thermal transmission.

Size-Tunable Assembly of Gold Nanoparticles Using Competitive AC Electrokinetics.

Alternating current (AC) electrokinetics is a facile way of patterning colloidal particles into advanced structures. We demonstrate the combined use of AC dielectrophoresis (AC-DEP) and AC electrohydrodynamics (AC-EHD) in a microwell electrode geometry for size-tunable assembly of gold nanoparticles (AuNPs) into one-dimensional microwires and two-dimensional films. The AC-DEP force scales with both particle size and field frequency, whereas the AC-EHD force depends only on the field frequency. So, a critical particle diameter ( dc) exists, below which the EHD phenomenon becomes more important and beyond which the DEP force is dominating. We performed theoretical and experimental studies to determine " dc" and how it gets affected by operating parameters like field frequency, voltage, particle number, electrolyte concentration, electrode size, and geometry. Our results show that the morphologies of the colloidal structures transition from films to microwires as the NP diameters vary from nanometers (< dc) to microns (> dc), and no assembly takes place at intermediate sizes (∼ dc). While the film formation is governed purely by surface EHD flows, microwire synthesis is a result of EHD-assisted DEP phenomenon. Also, a minimum particle number, a low salt concentration, and an optimum frequency range is required to initiate assembly.

A plasma‐fluid model for EHD flow in DBD actuators and experimental validation

SummaryA numerical method to simulate plasma induced electrohydrodynamic flow is proposed in this study. The numerical model consists of three components. Firstly, a potential module to simulate temporal potential and electric field generated in the ionized fluid. Secondly, a plasma module to simulate plasma development and charge particle densities. Finally, a fluid module to simulate the flow affected by the body forces induced by the movement of the charged particles. Fluid flow is modeled using modified predictor‐corrector strategy as proposed in the marker and cell method. The velocity field was corrected to achieve incompressible flow by calculating pressure correction factors, considered in all cells. Numerical convergence and time sensitivity analysis were carried to confirm grid independence and determine an efficient time step for simulations. Numerical computations are validated by comparing with experimental results of discharge currents and current densities. They were found to be in very good agreement thus providing an extensive validation. Furthermore, quiescent flow over a dielectric barrier discharge actuator is simulated in the this study, using the proposed plasma‐fluid model, to model flow evolution and resolve temporal flow features for detailed analysis. The streamline and vorticity plots were analyzed and compared with experimental results, and flow results were found to be in‐line with the experiments.

Application of Electric Field for Augmentation of Ferrofluid Heat Transfer in an Enclosure Including Double Moving Walls

Due to employing electric field, nanofluid heat transfer enhances. This phenomenon in a porous geometry has been simulated in this paper. To augment heat transfer, the radiation term is included in the model. Ethylene glycol nanofluid is considered as the homogenous model. Electric field and shape of nanoparticles can affect the properties of ferrofluid. CVFEM is proposed for simulating the treatment of EHD flow. Voltage, permeability, radiation parameters, and nanoparticles' shape are important variables. The results prove that the platelet shape leads to the highest convective flow. As electric force enhances, temperature gradient augments. Greater permeability leads to more convective flow.

Velocity field of EHD flow during back corona discharge in electrostatic precipitator

Particle Image Velocimetry studies of velocity field of the EHD flow during the back corona discharge at atmospheric pressure in an electrode system comprising a needle discharge electrode at negative potential and a grounded plate collection electrode covered with fly ash layer are presented in this paper. It was found that the magnitude of velocity vector of the EHD flow starting from the crater formed in fly ash layer after the onset of back corona discharge is of the same order of magnitude as for the flow generated by the corona discharge from the needle electrode. The measurements have shown that both these flows do not mix, but deflect each other off the axis of the needle electrode. The conclusion from this research is that the EHD deflection of the trajectories of particles flowing towards the collection electrode by the particles erupted from the crater at the collection electrode probably prevents those particles from the precipitation on the collection electrode that can result in a decreased collection efficiency of electrostatic precipitator during back corona discharge. This new mechanism has been called the “dynamic” process of the collection efficiency reduction.

A double-vortex EHD flow pattern generated by negative corona discharge in point-plane geometry

The paper presents the results of numerical simulation of the electrohydrodynamic flow in the point-plane configuration in air at atmospheric pressure and room temperature. A stationary corona discharge model considering three ionic species (electrons, negative and positive ions) includes four reactions in the ionization layer and doesn't use an assumption that the electric field on the corona electrode surface remains constant. The distributions of electric field and ionic species were used to calculate the electric body force and EHD flow. In addition to the well-known flow vortex in the drift zone, calculations predict the existence of an additional small vortex in the ionization layer. The effect of the voltage level on the flow pattern was also investigated.

Evaluation of EHD Flows Induced by Cationic Currents in CuSO&lt;sub&gt;4&lt;/sub&gt; Aqueous Solutions

Evaluation of EHD Flows Induced by Cationic Currents in CuSO&lt;sub&gt;4&lt;/sub&gt; Aqueous Solutions

Numerical investigation of using micropolar fluid model for EHD flow through a smooth channel

In this paper, a numerical method is presented to investigate the Electrohydrodynamic effect using micropolar fluid model. The EHD flow for the forced convection heat transfer in a smooth channel is simulated. The computed results were compared with the fully turbulent flow approach. It is found that the micropolar model can be used to simulate the hydraulically laminar flow. In addition, the heat transfer enhancement has the same efficiency for both the micropolar and the k-ε models. The change of the applied voltage and the Reynolds number caused various deviations of the results obtained from the two approaches up to a maximum of 20.79%, and a minimum of 0.03%.