The effect of uni/bipolar charge injection on EHD conduction pumping

Electrohydrodynamics (EHD) conduction pumping takes advantage of Coulomb force generated by externally applied electric field and dissociated charges from electrolytes present in the working fluid. With the electric field maintained below the DC breakdown limit (i.e voltage required for charge injection), EHD conduction generated flow relies primarily upon the asymmetry of the electrodes where the flow is always generated toward the specific direction regardless of the electrodes polarity. The charge distribution induced by the process of dissociation may be altered by charge injection, potentially present at the electrodes' surfaces. The charge injection could occur, for example, because of the electrode surface roughness.This paper is a numerical investigation to quantify the impact of the charge injection on the performance of EHD conduction pump. The numerical domain comprises a coplanar asymmetric electrode pair embedded against a 2-D channel wall where the EHD conduction induced liquid flow is expected to be generated from the narrower electrode toward the wider electrode in the absence of charge injection. The electric field, net charge density, and electric body force distributions are presented in the absence and presence of charge injection. In addition, the electrically generated net flow is calculated for several operating conditions.     

Control of adiabatic two-phase dielectric fluid flow distribution with EHD conduction pumping

Electrohydrodynamic (EHD) conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes, which are based on the process of dissociation of the neutral electrolytic species and recombination of the generated ions. This paper presents the successful control of dielectric liquid/vapor flow distribution between two parallel branch lines utilizing an EHD conduction pump at a select mass flux level under adiabatic condition.     

Analysis of the Electrohydrodynamic Flow in a Symmetric System of Electrodes by the Method of Dynamic Current–Voltage Characteristics

We have solved the problem of injection-type through electrohydrodynamic (EHD) flow in a closed channel. We have considered a model of a liquid with four types of ions. It is shown that a through EHD flow without internal vortices in the electrode gap is formed for the ratio 2 : 1 of the initial injection current from the electrodes in the channel. The structure of the flow in different parts of the channel and the integral characteristics of the flow have been analyzed. It is shown that for a quadratic function of injection at the electrodes, the current–voltage characteristic of the flow is also quadratic.     

Numerical investigation of using various electrode arrangements for amplifying the EHD enhanced heat transfer in a smooth channel

Forced convection heat transfer enhancement with electrohydrodynamic (EHD) technique of turbulent flow inside a smooth channel has been numerically investigated. A two dimensional numerical approach has been chosen to evaluate the local and average heat transfer coefficient. In addition, the swirling flow pattern in the presence of an electric field has been studied. To achieve higher enhancement while using multiple electrodes, variety of electrode arrangements have been examined for specified values of Reynolds number, applied voltage, and wire radius. The results demonstrate that different electrode arrangements cause significant improvement of the heat transfer coefficient.     

A fundamental characteristic and image analysis of liquid flow in an AW type EHD pump

Non-intrusive two-phase fluid pumping based on an electrohydrodynamically (EHD) induced flow phenomenon with free liquid surface exposed to gas-phase corona discharges is experimentally investigated. Dielectric liquid flow generated near a corona discharge electrode progresses toward an inclined plate electrode, and then climbs up the surface against the gravitational force for an air-wave (AW) type EHD pump. The AW type EHD pump is operated on ionic wind field along the inclined plate electrode. The pumping performance of time-averaged liquid flow rate and the liquid-phase flow motion are characterized. The liquid flow characteristics related to a dimensionless parameter of corona discharge fields are presented.     

Electrohydrodynamic flow in a wire-plate non-thermal plasma reactor measured by 3D PIV method

This work was aimed at measurements of the electrohydrodynamic (EHD) secondary flow in a non-thermal plasma reactor using three-dimensional particle image velocimetry (3D PIV) method. The wide-type non-thermal plasma reactor used in this work was an acrylic box with a wire discharge electrode and two plate collecting electrodes. The positive DC voltage was applied to the wire electrode through a 10 MΩ resistor. The collecting electrodes were grounded. The voltage applied to the wire electrode was 28 kV. Air flow seeded with a cigarette smoke was blown along the reactor duct with an average velocity of 0.6 m/s. The 3D PIV velocity fields measurements were carried out in four parallel planes stretched along the reactor duct, perpendicularly to the wire electrode and plate electrodes. The measured flow velocity fields illustrate complex nature of the EHD induced secondary flow in the non-thermal plasma reactor.     

On-set of EHD turbulence for cylinder in cross flow under corona discharges

Experimental and theoretical investigations have been conducted for the on-set of electrohydrodynamically (EHD) induced turbulence for cylinder in cross flow. The experiments were conducted for Reynolds numbers from 0.2 to 80 based on cylinder diameters, and Reynolds numbers from 10³ to 4×10³ based on the flow channel width. This flow conditions represent laminar to transitional-flow before the on-set of the EHD-turbulent flow. Theoretical analysis was based on the mass, momentum, and charged particle conservation equations coupled with the Poisson's equation for electric field evaluation. The results showed that: (1) on-set of EHD turbulence is initiated near the real-stagnation point; (2) EHD turbulence can be generated even for Reynolds numbers (Re) less than 0.2, if the EHD number (Ehd) is larger than the critical Reynolds number square (Ehd>Re²); and (3) the electrical origin of instability, which is leading into the on-set of turbulence can be estimated from Ehd/Db²>Re² relation, where Db is the Debye number.     

Effect of micropillar electrode spacing on the performance of electrohydrodynamic micropumps

Electrohydrodynamic (EHD) micropumps with three-dimensional 50 μm × 50 μm micropillar electrodes were fabricated and tested in this study. Two basic electrode configurations were investigated: (i) micropillar emitter and collector electrodes (symmetric) and (ii) micropillar emitter and planar collector electrodes (asymmetric). The micropumps were fabricated by integrating chromium/gold planar electrodes with electroplated 3-D Nickel micropillars on a glass substrate with a 100 μm high PDMS microchannel. The effect of the spanwise micropillar spacing on the pump performance was determined. The pumps were tested using HFE-7100 as the working fluid for the maximum pressure generation under a no flow condition. The micropumps with the asymmetric electrode design generated a significantly higher pressure head than the corresponding micropumps with symmetric electrode configuration for the same applied voltage, with lower power consumption. A decrease in the spanwise spacing of the micropillar electrodes increased the pump performance for the symmetric configuration, while the performance decreased for the asymmetric configuration.     

One model of electric conduction and electric field distributions in a liquid insulator

The electric properties of the liquid insulator have been studied in this work. We have described the time-dependent model of the conduction processes in the liquid insulator under high voltages. Our model is a generalization of the Frenkel conduction model. (The last deals only with stationary conduction processes). Calculation of the electric field has also been made for two types of problems: (1) the external electric field applied to a liquid, is created by plane electrodes. (2) A spherical electrode of a small size creates it. The electrodes are assumed to be under constant high voltage. There is no electron emission or ion injection from the electrodes. But the field intensity influences on the molecular dissociation rate, and this fact has been taken into account. We have shown that the space charge, which arises under conditions mentioned above gives rise to changes in the electric field distribution. The model on hand is also used for calculating the hydrodynamic phenomena under high non-uniform electric field intensities. It has also been shown that the velocity of the strong EHD flows is proportional to the value of direct current or the squared value of applied voltage.     

Flow control with plasma-based actuator in different velocity regimes: Momentum and heat transfer effects

In this study, control of the airflow by the direct current (DC) electrical discharge with bare electrodes has been investigated in different velocity regimes. The discharge characteristics of the plasma model are obtained numerically. An induced electrohydrodynamic (EHD) force on neutral flow was characterized based on momentum transfer from charged particles. The change in the incident flow parameters was studied by applying Navier–Stokes (N-S) equations, considering source terms arising from a weakly ionized plasma. The effect of the discharge on the low- and high-speed flow was simulated in this study. It was concluded that the changes of the velocity profile, airflow pressure, and oblique shock wave could be attributed to the EHD force from a nonthermal plasma to the incoming airflow. It was seen that the incident airflow is accelerated also by the induced EHD force. Our results show that the most important mechanism in the plasma-based flow control is the momentum transfer from the electrical discharge to the incident flow and that the gas heating has no significant role.     

电液动力微泵的改进

介绍了微型电液动力泵的优化设计和工艺改进。电液动力微泵制作工艺的改进包括:材料的选择,微电极的优化设计和封装工艺的改进。使用聚二甲基硅氧烷(PDMS)作为构建微流道的材料,采用浇注法制作了PDMS微流道,并采用阳极键合方式进行微泵的封装。使用无水乙醇为工作流体对微泵进行流动实验,在驱动电压为90 V时,电液动力微泵驱动流体的最大流速可以达到92 uL/min。     

EHD flow in a wide electrode spacing spike–plate electrostatic precipitator under positive polarity

In this work, results of two- and three-dimensional particle image velocimetry (PIV) measurements of the flow velocity fields in a wide spacing spike–plate electrostatic precipitator (ESP) under positive polarity are presented. A DC voltage of positive polarity (up to 28 kV) was applied to the spike electrode. The average gas flow velocity was 0.6 m/s. The PIV measurements were carried out in four planes perpendicular to the plate electrodes. Three parallel planes passed along the ESP while one plane passed across the ESP duct. The results show that electrohydrodynamic (EHD) secondary flow with relatively strong vortices exist in the ESP. The EHD secondary flow pattern depends on applied voltage and measuring plane position in respect to the spike tip. The strongest vortices occur in the plane passing through the tip of the upstream-directed spike. These relatively strong EHD vortices may hinder collection of the particles in the diameter range of 0.1–1 μm in the wide electrode spacing spike–plate ESPs.     

Cost-effective fabrication of memristive devices with ZnO thin film using printed electronics technologies

A prototype memristive device has been presented in this paper, for which the top and bottom electrodes have been fabricated through a simple and cost-effective technique, i.e. electrohydrodynamic printing. For deposition of the bottom electrode pattern, a silver ink containing 60 wt% silver by content was subjected to controlled flow through a metal capillary exposed to an electric field at the ambient temperature to generate an electrohydrodynamic jet, thereby depositing uniform patterns of silver on glass substrate at a constant substrate speed. The top electrode has been deposited in a similar fashion. In between the top and bottom electrodes, a uniform layer of ZnO is fabricated using spin-coating technique. The nanoscale ZnO memristor stack has a channel length of 370 μm and channel width of 82 μm. A memristor thus fabricated was characterized and its current voltage curves were analyzed. The device showed a typical nonvolatile resistive switching behavior present in memristor devices thus highlighting the EHD printed patterning as a reliable method for the fabrication of memory devices.     

A charge-conservative approach for simulating electrohydrodynamic two-phase flows using volume-of-fluid

In the present study we propose a charge-conservative scheme to solve two-phase electrohydrodynamic (EHD) problems using the volume-of-fluid (VOF) method. EHD problems are usually simplified by assuming that the fluids involved are purely dielectric (insulators) or purely conducting. Gases can be considered as perfect insulators but pure dielectric liquids do not exist in nature and insulating liquids have to be approximated using the “Taylor–Melcher leaky dielectric model” [1], [2] in which a leakage of charge through the liquid due to ohmic conduction is allowed. It is also a customary assumption to neglect the convection of charge against the ohmic conduction. The scheme proposed in this article can deal with any EHD problem since it does not rely on any of the above simplifications. An unrestricted EHD solver requires not only to incorporate electric forces in the Navier–Stokes equations, but also to consider the charge migration due to both conduction and convection in the electric charge conservation equation [3]. The conducting or insulating nature of the fluids arise on their own as a result of their electric and fluid mechanical properties. The EHD solver has been built as an extension to Gerris, a free software solver for the solution of incompressible fluid motion using an adaptive VOF method on octree meshes developed by Popinet [4], [5].     

Compact polymer multi-nozzles electrospray device with integrated microfluidic feeding system

Electrohydrodynamic (EHD) atomization consists in using an electric field for spraying a liquid flowing through a capillary. The applications are: mass spectrometry, colloid thrusters and more recently medicine nebulization processes. EHD atomization provides the ability to control the generated droplets size by adjusting electrospray parameters. It is however essential to manufacture the emitters into arrays because flow through a stable cone-jet mode electrospray can only be maintained at low flow rate and most applications require a high throughput. We propose a new design of a multiple electrospray system involving an innovative nozzle shape and flow restrictor system. Nozzles and microfluidic restrictor system are manufactured on the same polycarbonate sheet using the excimer laser technology and thus allowing a high compactness of this system.     

Effect of emitting electrode number on the performance of EHD gas pump in a rectangular channel

Previous studies have shown that electric field in the form of corona wind can be used for gas pumping. It has also been shown that the maximal volume flow rate can be achieved by an optimal design and arrangement of electrode(s) involved. In this study, the number of emitting electrodes has been considered for its effects on the pump performance. To seek the relation between the electrode number and pump performance, an EHD gas pump with three configurations (4, 12, and 28 emitting electrodes) is critically evaluated by experimental measurements and numerical simulations.     

Effect of nonequilibrium near-electrode layers on the structure of EHD flows in the three-ions model of a dielectric liquid

An electrohydrodynamic (EHD) flow is a spontaneous flow of a liquid in the electrode gap under the action of a strong electric field. Most experimental data from an investigation of the velocity field of EHD flows were obtained in the wire-over-plane electrode configuration. For this system, the flow can be treated as a 2D flow. We report on the results of a computer simulation of the complete system of electrohydrodynamics equations in the three-ion model of a dielectric liquid. The structure of nonequilibrium dissociation–recombination layers and their effect on the structure of EHD flows have been analyzed based on the results of the computer simulation of EHD flows in liquids with different low-voltage conductivities for the wireover- plane electrode system.     

Performance characteristics between horizontally and vertically oriented electrodes EHD ESP for collection of low-resistive diesel particulates

The novel electrohydrodynamically-assisted electrostatic precipitator (EHD ESP) was developed to suppress particle reentrainment for collection of low resistive diesel particulates. The collection efficiency was compared between vertically and horizontally oriented electrodes of the EHD ESP using 400 cc diesel engine. The particle size dependent collection efficiency was evaluated for the particle size ranging in 20 to 5000 nm using a scanning mobility particle sizer (SMPS) and a particle counter (PC). Both horizontally and vertically oriented EHD ESP showed an excellent suppression of particle reentrainment. However, the horizontally oriented electrode EHD ESP showed significantly improved for the particle size of 300–500 nm in comparison with vertically oriented electrode EHD ESP, resulting in more than 90% collection efficiency for all particle size range. The EHD ESP has high potential especially for highly concentrated marine diesel engine emission control.     

EHD flow measured by 3D PIV in a narrow electrostatic precipitator with longitudinal-to-flow wire electrode and smooth or flocking grounded plane electrode

In this work, results of three-dimensional (3D) Particle Image Velocimetry (PIV) measurements of the electrohydrodynamic (EHD) flow velocity fields in a narrow electrostatic precipitator (ESP) with a longitudinal-to-flow placed wire electrode are presented. The ESP was a narrow transparent acrylic box (90 mm×30 mm×30 mm). The electrode set consisted of a single wire discharge electrode and two plane collecting electrodes. Either two smooth stainless-steel plates or two stainless-steel plane meshes with nylon flocks were used as the collecting electrodes. The 3D PIV measurements were carried out in two parallel planes, placed longitudinally to the flow duct. The positive DC voltage of up to 9.5 kV was applied to the wire electrode through a 10 MΩ resistor. The collecting electrodes were grounded. The measurements were carried out at a primary flow velocity of 0.5 m/s. Obtained results show that the flow patterns for the smooth-plate electrodes and for the flocking plane electrodes are similar in the bulk of the flow. However, the flow velocities near the flocking plane electrodes are much lower than those near the smooth-plate electrodes. This is a beneficial phenomenon, because the lower the flow near the collecting electrodes, the lower re-entrainment of the particles deposited on the collecting electrodes occurs.     

Self-consistent surface calculation of electron-hole drops in gallium phosphide

Self-consistent Kohn-Sham method is used to investigate the surface structure of electron-hole drops (EHD) in GaP. If the conduction bands are located on the X-point and have a degeneracy of 3, the surface tension is found to be 85 × 10^?4 erg cm^?2. In the presence of a “camel's-back” structure and a conduction band degeneracy of 6, the surface tension is calculated to be 130 × 10^?4 erg cm^?2. The surface charge on the EHD is found to be negative irrespective of whether the conduction band degeneracy is 3 or 6.