Showing papers on "Liquid dielectric published in 2009"

Effect of micro-powder suspension and ultrasonic vibration of dielectric fluid in micro-EDM processes—Taguchi approach

Abstract: Solutions are needed for increasing the material removal rate without degrading surface quality in micro-electrical discharge machining (μ-EDM). This paper presents a new method that consists of suspending micro-MoS 2 powder in dielectric fluid and using ultrasonic vibration during μ-EDM processes. The Taguchi method is adopted to ascertain the optimal process parameters to increase the material removal rate of dielectric fluid containing micro-powder in μ-EDM using a L 18 orthogonal array. Pareto analysis of variance is employed to analyze the four machining process parameters: ultrasonic vibration of the dielectric fluid, concentration of micro-powder, tool electrode materials, and workpiece materials. The results show that the introduction of MoS 2 micro-powder in dielectric fluid and using ultrasonic vibration significantly increase the material removal rate and improves surface quality by providing a flat surface free of black carbon spots.

Dielectric heating in insulating materials subjected to voltage waveforms with high harmonic content

Abstract: Dielectric heating is one potential aging mechanism active below partial discharge inception voltage in materials used as high voltage insulation. When exposed to voltage waveforms containing high amount of harmonics, the heat generation will be larger due to increased power losses as compared with power frequency excitation. This may result in a decreased life or even failure of insulation due to the increased operating temperature or to thermal runaway. An analysis of the power developed due to dielectric heating in two different materials subjected to voltage waveforms with high harmonic content is presented in this paper. By expressing the non-sinusoidal loss as an enhancement factor to the sinusoidal one, a geometry-independent formalism is derived. From dielectric response measurements at low voltage and at several temperatures the dielectric power loss in the material can be calculated for different voltage levels and waveforms. Two important material parameters can be extracted from the calculated dielectric power loss: (i) non-sinusoidal loss compared with sinusoidal loss with the same fundamental frequency (pfact) and (ii) change of loss with changing temperature (dpfact/dT). These two parameters could potentially be used to indicate the suitability of materials for use in applications where voltage waveforms contain high harmonic content.

White Layer Composition, Heat Treatment, and Crack Formation in Electric Discharge Machining Process

Abstract: Characteristics of electric discharge machined (EDM) surfaces of normalized, quenched, and quenched and tempered-treated steels in kerosene and deionized-water dielectric liquids are investigated Optical microscopy, scanning electron microscopy (SEM) and X-ray diffractometry are employed to analyze the machined surface Surface cracks are examined in terms of white layer composition, heat treatment of the workpiece material, and operational parameters used, such as average discharge current and pulse-on duration The present results reveal that base material properties and white layer composition have a distinctive function on crack formation that results in different crack network layouts on the surface and penetration depths in the substrate Surface cracks, which initiate at the surface, travel down perpendicularly toward the interferential zone, and terminate at this interference, are mainly formed due to an increase in nonhomogeneities of metallurgical phases within the white layer Such cracks are usually encountered on the surfaces when machining is performed in a hydrocarbon-based dielectric liquid using high pulse-on duration and low average discharge current On the other hand, penetrating cracks, which penetrate the entire white layer thickness to an extent into the parent material, are mainly formed due to contraction of the recast structure joined to the circumferential edge of a crater rim during solidification This type of crack is common when machining is performed in deionized water and the work material is brittle Crack penetration depth is found to be proportional to the used pulse energy, and its path has a tendency to form parallel cracks to the machined surface at decreased pulse-on duration

Dielectric liquid microlens with well-shaped electrode.

Abstract: A dielectric liquid microlens with a well-shaped electrode is demonstrated. The bottom well-shaped electrode and the top planar electrode induce an inhomogeneous electric field when a voltage is applied, which causes the focal length to change. Adaptive microlenses and microlens arrays with well-shaped electrode are fabricated and their performance is evaluated. The bi-convex structure introduces a larger optical power. Compared with common planar-electrodes liquid lenses, this well-shaped electrode not only inhibits drifting of the liquid but also reduces the operating voltage.

Theory of the Maxwell pressure tensor and the tension in a water bridge

Abstract: A water bridge refers to an experimental "flexible cable" made up of pure de-ionized water, which can hang across two supports maintained with a sufficiently large voltage difference. The resulting electric fields within the de-ionized water flexible cable maintain a tension that sustains the water against the downward force of gravity. A detailed calculation of the water bridge tension will be provided in terms of the Maxwell pressure tensor in a dielectric fluid medium. General properties of the dielectric liquid pressure tensor are discussed along with unusual features of dielectric fluid Bernoulli flows in an electric field. The "frictionless" Bernoulli flow is closely analogous to that of a superfluid.

Electrically Induced Dielectric Liquid Film Flow Based on Electric Conduction Phenomenon

Abstract: Electrohydrodynamic (EHD) conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes, generated by the process of dissociation of the neutral electrolytic species and recombination of the generated ions. The theoretical formulation for EHD conduction pumping of liquid film is presented and fundamentally analyzed with the aid of numerical solutions. This model includes fluid dynamics governing equations under laminar and isothermal conditions which are modified to account for the presence of electric body force. The model also includes charge transport equations which are related to the dissociation/recombination phenomenon along with Maxwell's relations that govern the electric field distribution. This paper determines how liquid film flow is generated based on the electric conduction phenomenon. Specifically, the role of controlling dimensionless parameters on the heterocharge layers and flow structures along with the impact of liquid film velocity on charge distribution are illustrated and fundamentally analyzed. In addition, the contribution of unique electrode designs toward electric body force distribution and flow pattern is investigated followed by the effect of interaction between adjacent electrode pairs in multi-pair configurations on generated flow rate. Further, a brief discussion of the conduction pumping efficiency is presented. Finally, the numerical results are verified against experimental data.

Axisymmetric and non-axisymmetric instability of an electrified viscous coaxial jet

Abstract: A linear study is carried out for the axisymmetric and non-axisymmetric instability of a viscous coaxial jet in a radial electric field. The outer liquid is considered to be a leaky dielectric and the inner a perfect dielectric. The generalized eigenvalue problem is solved and the growth rate of disturbance is obtained by using Chebyshev spectral collocation method. The effects of the radial electric field, liquid viscosity, surface tension as well as other parameters on the instability of the jet are investigated. The radial electric field is found to have a strong destabilizing effect on non-axisymmetric modes, especially those having smaller azimuthal wavenumbers. The helical mode becomes prevalent over other modes when the electric field is sufficiently large. Non-axisymmetric modes with high azimuthal wavenumbers may be the most unstable at zero wavenumber. Liquid viscosity has a strong stabilizing effect on both the axisymmetric and non-axisymmetric instability. Relatively, the helical instability is less suppressed and therefore becomes predominant at high liquid viscosity. Surface tension promotes the instability of the para-sinuous mode and meanwhile suppresses the helical and the other non-axisymmetric modes in long wavelength region.

Apparatus and method with forced coolant vapor movement for facilitating two-phase cooling of an electronic device

Abstract: Apparatus and method are provided for two-phase dielectric cooling of an electronic device. The apparatus includes a coolant flow path, a vapor condenser and one or more vapor fans. The coolant flow path is in fluid communication with the electronic device, where liquid dielectric coolant within the flow path vaporizes upon contacting the electronic device, forming dielectric coolant vapor, and thereby facilitating cooling of the electronic device. The vapor condenser is also in fluid communication with the coolant flow path and facilitates condensate formation from the dielectric coolant vapor. The one or more vapor fans are disposed within the flow path to actively move dielectric coolant vapor into contact with the vapor condenser, and thereby enhance cooling of the electronic device by facilitating coolant condensate formation and thus recirculation of the coolant condensate as liquid dielectric coolant.

Geometry and surface damage in micro electrical discharge machining of micro-holes

Abstract: Geometry and subsurface damage of blind micro-holes produced by micro electrical discharge machining (micro-EDM) is investigated experimentally to explore the relational dependence with respect to pulse energy. For this purpose, micro-holes are machined with various pulse energies on plastic mold steel samples using a tungsten carbide tool electrode and a hydrocarbon-based dielectric liquid. Variations in the micro-hole geometry, micro-hole depth and over-cut in micro-hole diameter are measured. Then, unconventional etching agents are applied on the cross sections to examine micro structural alterations within the substrate. It is observed that the heat-damaged segment is composed of three distinctive layers, which have relatively high thicknesses and vary noticeably with respect to the drilling depth. Crack formation is identified on some sections of the micro-holes even by utilizing low pulse energies during machining. It is concluded that the cracking mechanism is different from cracks encountered on the surfaces when machining is performed by using the conventional EDM process. Moreover, an electrically conductive bridge between work material and debris particles is possible at the end tip during machining which leads to electric discharges between the piled segments of debris particles and the tool electrode during discharging.

PIV measurements on charged plumes-influence of SiO 2 seeding particles on the electrical behavior

Abstract: It is well known that an isothermal dielectric liquid can be driven by electroconvection. It has been demonstrated that two phenomena could generate space charge in isothermal dielectric liquids and then induce a fluid movement. These two electroconvective effects are bulk conduction and ion injection. In order to improve the performance of electroconvective devices, the velocity of the flows must be recorded as accurately and precisely as possible. In this paper, the particle image velocimetry (PIV) method that was originally developed in the field of experimental fluid mechanics is adapted to electroconvective flow measurements. The choice and the size of seeding particles are discussed. The influence of the seeding particles density on the current is measured. In this work, experiments were investigated on a typical two-dimensional charged plume flow produced between a blade and a flat plate. Both negative and positive polarities are also investigated.

Reversible thermal interfaces based on microscale dielectric liquid layers

Abstract: We present a reversible thermal interface that can circumvent limitations of direct solid-solid contacts. A thin continuous layer of a dielectric liquid is formed between two solid substrates to provide a low-resistance heat conduction path. The liquid is initially confined in an array of discrete microchannels and undergoes reversible morphological transition into a continuous film as the loading pressure is increased. We theoretically and experimentally determine the relationship between loading pressure and liquid morphology. The interfaces can achieve thermal resistance comparable to that of solid-solid contacts but at loading pressures orders of magnitude smaller.

Fluid cooled choke dielectric and coaxial cable dielectric

Abstract: The microwave antenna assembly includes a feedline electrically connected to an elongated shaft by a choke electrical connector. The feedline includes an inner conductor, an outer conductor, an elongated shaft and a choke electrical connector. The inner conductor is disposed in coaxial arrangement with the inner conductor and forms a dielectric supply lumen therebetween. The elongated shaft at least partially surrounding the feedline and form a dielectric return lumen therebetween. The choke electrical connector surrounds at least a portion of the feedline and electrically connects the feedline outer conductor to the elongated shaft. A low-loss dielectric fluid is supplied between the inner conductor and the outer conductor of the feedline and forms a dielectric barrier therebetween. The low-loss dielectric fluid also forms a dielectric barrier between the outer conductor of the feedline and the elongated shaft and the choke electrical connector forms a plurality of apertures extending therethrough, the apertures forming at least a portion of the dielectric return lumen.

A novel actuation method of transporting droplets by using electrical charging of droplet in a dielectric fluid.

Abstract: We evaluate the feasibility of manipulating droplets in two dimensions by exploiting Coulombic forces acting on conductive droplets immersed in a dielectric fluid. When a droplet suspended in an immiscible fluid is located near an electrode under a dc voltage, the droplet can be charged by direct contact, by charge transfer along an electrically conducting path, or by both mechanisms. This process is called electrical charging of droplet (ECOD). This charged droplet may then be transported rapidly by exploiting Coulombic forces. We experimentally demonstrate electrical actuation of a charged droplet by applying voltage sequences. A charged droplet is two dimensionally actuated by following the direction of the electrical field signal. The droplet does not contact the surface of the microfluidic chip when it moves. This characteristic is very advantageous because treatments of the substrate surfaces of microfluidic chip become simpler. In order to test the feasibility of using ECOD in a droplet-based microreactor, electrocoalescence of two oppositely charged droplets is also studied. When two droplets approach each other due to Coulombic attraction, a liquid bridge is formed between them. We postulate that if the applied electric field is weaker than a certain critical level, the two droplets coalesce instantaneously when the charges are exchanged and redistributed through this liquid bridge.

Influence of dielectric properties on van der Waals/Casimir forces in solid-liquid systems

Abstract: In this paper, we present calculations of van der Waals/Casimir forces, described by Lifshitz theory, for the solid-liquid-solid system using measured dielectric functions of all involved materials for the wavelength range from millimeters down to subnanometers. It is shown that even if the dielectric function is known over all relevant frequency ranges, the scatter in the dielectric data can lead to very large scatter in the calculated van der Waals/Casimir forces. Especially when the liquid dielectric function becomes comparable in magnitude to the dielectric function of one of the interacting solids, the associated variation in the force can be up to a factor of 2 for plate-plate separations 5-500 nm. This corresponds to an uncertainty up to 100% in the theory prediction for a specific system. As a result accuracy testing of the Lifshitz theory under these circumstances is rather questionable. Finally we discuss predictions of Lifshitz theory regarding multiple repulsive-attractive transitions with separation distance, as well as nontrivial scaling of the van der Waals/Casimir force with distance.

High voltage isolation and cooling for an inductively coupled plasma ion source

Abstract: A plasma source for processing or imaging a substrate, for ion source for proton therapy, for ion thrusters, or for high energy particle accelerators includes a coolant circuit passing adjacent to a plasma ion reactor chamber and RF antenna coils. In a method for operating the plasma ion source having an induction coil adjacent to a reaction chamber for inductively coupling power into the plasma from a radio frequency power source, the method comprises pumping a dielectric fluid into contact with induction coils of the plasma ion source along the coolant circuit. Use of the dielectric fluid both electrically insulates the plasma chamber, so that it can be biased to 30 kV and up, and efficiently transfers heat away from the plasma chamber.

Nonlinear Waves on the Surface of a Dielectric Liquid in a Horizontal Electric Field in 3D Geometry: Exact Solutions

Abstract: It has been shown that waves of arbitrary configuration in 3D geometry may propagate without distortion along the surface of a dielectric liquid in the direction of a horizontal electric field. This situation occurs for the high-permittivity liquids in the case of a sufficiently high external field when the effect of electrostatic forces dominates. A general solution of the equations of motion that describes the interaction of counterpropagating waves of a small but finite amplitude has been obtained.

Dielectric fluid filled active implantable medical devices

Abstract: Active implantable medical devices (AIMDs) are backfilled with a dielectric fluid to increase the volts per mil dielectric breakdown strength between internal circuit elements. In a method for backfilling the AIMD with dielectric fluid, substantially all air and moisture is evacuated from the AIMD housing prior to backfilling the AIMD housing with a dielectric fluid having a dielectric breakdown strength greater than air, nitrogen or helium. The AIMD is constructed to accommodate volumetric expansion or contraction of the dielectric fluid due to changes of pressure or temperature of the dielectric fluid to maintain integrity of the AIMD.

Planar Liquid Confinement for Optical Centering of Dielectric Liquid Lenses

Abstract: In this letter, planar liquid confinement structures along with concentric electrodes are proposed for the optical centering of dielectric liquid lenses at the rest state and during actuation. Both the liquid confinement structures and electrodes that are photolithographically fabricated on glass substrates share the same geometric center, thereby minimizing the deviation of the optical axis at all operation modes. Tilt angles of mesa liquid confinement structure are experimentally found to be 0.11deg in maximum and below 0.03deg during actuation for a liquid lens with a droplet of initially 7 mm in diameter.

Effect of material properties on reverse flow in nematic liquid crystal devices with homeotropic alignment

Abstract: Reverse flow is undesirable in liquid crystal devices with vertical alignment. The influence of the material properties on the onset of backflow is investigated for commercially available negative dielectric liquid crystals. It is shown that the threshold voltage VBF for the occurrence of backflow is an important material characteristic. This threshold is relevant for applications and a large value is desired in devices to avoid backflow while keeping a wide applicable voltage range. Accurate finite element simulation of the liquid crystal hydrodynamics allows extraction of VBF and the unknown Miesowicz coefficients ηij. The resulting values are tabulated at 20.0 °C.

Effect of Thermal Modulation on the Onset of Electrothermoconvection in a Dielectric Fluid Saturated Porous Medium

Abstract: An electroconvection in a horizontal dielectric fluid saturated with a densely packed porous layer is investigated under the simultaneous action of vertical electric field and vertical temperature gradient when the walls of the layer are subjected to time periodic temperature modulation. The dielectric constant is assumed to be a linear function of temperature. A regular perturbation method based on small amplitude of applied temperature field is used to compute the critical values of Rayleigh number and wave number. The shift in the critical Rayleigh number is calculated as a function of frequency of modulation, electric Rayleigh number, Prandtl number, and Darcy number, and their effects on the critical Rayleigh number are discussed. The situations which are favorable for the design of artificial organs without the side effect of hemolysis are explained. Copyright © 2009 by ASME.

Organogel for electrical cable insulating layer

Abstract: The present invention relates to an electric cable comprising at least one conductor (10), and an electrically insulating layer impregnated with a dielectric fluid (12), said insulating layer (12) surrounding said conductor (10), the dielectric fluid comprising an organogel including an oil and an organo-gelator, characterized in that the oil is a non-polar oil with a flash point inferior or equal to 200°C.

Progress report on natural esters for distribution and power transformers

Abstract: Natural ester seed oil based dielectric fluid is an environmentally advantaged fluid that is increasingly being used as a replacement for mineral oil and for high temperature flashpoint liquids, including silicone and R-TEMP. This report updates experience with use of the fluid over the last two years. Considerable studies have been conducted to investigate heat aging performance of cellulose, electrical contact thermal stability, dielectric strength, moisture sensitivity, and cold temperature performance. A series of reports presents a summary of work that has been completed to date and examines customer experience with the use of Natural Esters in real transformers. The work contains both new transformers and retro-fills in Distribution and Power Transformers as well as Step Voltage Regulators and Switchgear.

Effects of Moisture Content in a Dielectric Liquid on Electrohydrodynamic Pumping

Abstract: The effects of various moisture contents (ranging from 50 to 2500 ppm) in a dielectric liquid on electrohydrodynamic (EHD) pumping have been investigated. The static pressure and the flow rate induced by the EHD pump were examined using dibutyl sebacate (DBS) as the working fluid. One of the additives in DBS was deionized water. It was found that the pressure head induced by the EHD pump was significantly sensitive to different moisture contents. A simple predictive model was derived using the Coulomb force and a linear dielectric increment approximation. This model predicted that the static pressure increases linearly in line with the greater moisture contents due to the high dielectric constant of deionized water. It was observed that the pressure, as a function of moisture content, behaves in a similar manner.

Droplet creation using liquid dielectrophoresis

Abstract: Dielectrophoresis (DEP) is defined as polarizable particles moving into regions of higher electric field intensity. In liquid DEP (LDEP), a dielectric liquid tends to flow toward regions of high electric field intensity under a non-uniform electric field. This work presents a theoretical model of LDEP based on parallel electrodes. The LDEP force is derived using the lump parameter electromechanical method. The relationship between the minimum actuation voltage and the electrode width is investigated experimentally and theoretically. We also propose a method for creating a 20 nl droplet of deionized water using LDEP. The creation of a water droplet containing 15 μm polystyrene beads is placed at the desired location from a continuous flow driven by LDEP using the developed method.

An experimental study on the effect of DC bias on streamer initiation and propagation in a dielectric liquid under impulse voltage

Abstract: The role of composite voltage waveforms on prebreakdown processes was studied at atmospheric conditions in a small point-plane gap with a synthetic ester Midel 7131 fluid, representing a model for the insulation in power electronic components. Shadowgraphic imaging and photomultipliers to record emitted light were used to measure streamer initiation voltages, streamer propagation lengths and velocities. The applied voltages were step voltages (100 ns rise time) with or without a dc bias. Results have demonstrated the presence of space charges in the vicinity of electrodes. With a step voltage with the same polarity as the dc prestress, initiation voltages increased and propagation lengths were reduced. For a polarity reversal for positive steps the initiation voltages were reduced and propagation lengths increased as expected, while for negative step the opposite was seen. The latter is explained by an electron "cleaning" effect of the positive dc prestress reducing possibilities for electron avalanches. It is shown that streamers may be initiated by a sudden turn off of a dc stress.