Showing papers on "Liquid dielectric published in 2003"

Equilibrium behavior of sessile drops under surface tension, applied external fields, and material variations

Abstract: This article describes the equilibrium shape of a liquiddrop under applied fields such as gravity and electrical fields, taking into account material properties such as dielectric constants, resistivities, and surface tension coefficients. The analysis is based on an energy minimization framework. A rigorous and exact link is provided between the energy function corresponding to any given physical phenomena, and the resulting shape and size dependent force term in Young’s equation. In particular, the framework shows that a physical effect, such as capacitive energy storage in the liquid, will lead to 1/R “line-tension”-type terms if and only if the energy of the effect is proportional to the radius of the liquiddrop: E∝R. The effect of applied electric fields on shape change is analyzed. It is shown that a dielectric solid and a perfectly conducting liquid are all that is needed to exactly recover the Young–Lippmann equation. A dielectric liquid on a conducting solid gives rise to line tension terms. Finally, a slightly resistiveliquid on top of a dielectric, highly resistive solid gives rise to contact angle saturation and accurately matches the experimental data that we observe in our electro-wetting-on-dielectric devices.

Electrohydrodynamically induced dielectric liquid flow through pure conduction in point/plane geometry

Abstract: Mildly polar liquids generally exhibit an ohmic behavior when subjected to electric fields of limited values. The resulting conduction is then associated with heterocharge layers of finite thickness in the vicinity of the electrodes. In the absence of charge injection or induction, a simple conduction model based on the processes of dissociation of a neutral electrolytic species and recombination of the generated ions is presented. This model is first applied to parallel plane electrode geometry to describe the build-up of the heterocharge. Then, the case of point/plane configuration is considered where the effect of Coulomb force is different in the two layers next to the electrodes. A net motion toward the point electrode is predicted to occur. With a rough approximation for the harmonic field, an analysis is presented which leads to an expression for the axial component of the net force exerted on the liquid. A simple static pump is designed and built to experimentally investigate the pressure head generated through pure conduction. Two working fluids (refrigerant R-123 and n-hexane) and two different electrode designs are considered in this study. The experimental results are qualitatively compared to the theoretical predictions.

Impact of air bubbles in a dielectric liquid when subjected to high field strengths

Abstract: The dielectric breakdown of gas bubbles entrapped in liquid food flowing through the cavity of a pulsed electric field treatment chamber has been a limiting factor in this non-thermal food preservation technology. Prediction of electric field enhancement due to gas bubbles is an important tool in the design, modification, and optimization of the treatment chamber's electrode geometry and pressurization. Simulation of the electrostatic characteristics of a coaxial treatment chamber with specified voltage of 25 kV, filled with dielectric material with conductivity of 0.6 S/m containing gas bubbles, evidenced a significant perturbation in the electric field. The magnitude of electric fields generated inside the bubbles was almost two times higher than in the homogeneous food. Without pressurization (atmospheric conditions), the dielectric breakdown strength of the gas-filled bubbles was exceeded, thus indicating the risk of arcing. A system pressurization of approximately 8 atm could be sufficient to limit arcing when small gas bubbles (∼1 mm) are present. The presence of gas bubbles caused the field magnitude to decrease significantly near the boundary of the bubble, thus threatening the uniformity of the PEF treatment across the chamber gap. This perturbation in the electric field was more significant when more than one bubble was present or when smaller gaps were used. The dielectric breakdown threshold at a given pressure is more likely to be exceeded by bigger bubbles (>1 mm) entrapped in a fluid processed in smaller treatment chamber gaps (3 mm), than by smaller bubbles (

Furanic compounds in dielectric liquid samples: review and update of diagnostic interpretation and estimation of insulation ageing

Abstract: Commercial laboratories and electrical equipment owners have used analysis of furanic compounds in dielectric liquids for more than ten years to evaluate the continuing operation of transformers and to estimate the degree of ageing of solid insulation. The solid insulation of transformers is comprised mainly of Kraft paper. As the paper ages, the cellulose polymer chains break down into shorter lengths with a corresponding decrease in both tensile strength and degree of polymerization. Further, the paper breakdown is accompanied by an increase in the content of various furanic compounds in the dielectric liquid. Analysis for furanic compounds allows the laboratory or the owner to make a determination as to whether the breakdown of the paper is an active condition. It further allows a determination as to the relative degree of the paper breakdown that has occurred. This paper reviews the tools that have evolved to help perform these interpretations and presents a system to aid in the assessment of transformer insulation ageing.

Point-to-plane discharge dynamics in the presence of dielectric droplets

Abstract: The effects of dielectric liquid droplets on the electrodynamics of the streamer-induced discharges under high voltage pulses in a non-uniform electric field are investigated in air at atmospheric pressure. Owing to electrical and optical correlated measurements, changes in the properties of streamer development have been described. It has been shown that a jet of droplets can have a guiding action and a velocity increase effect on streamer advancement, as well as a reduction of the voltage range where streamers develop. The streamer threshold potentials are globally higher when droplets lie close to the positive point electrode and the critical potentials beyond which a streamer leads to an arc development are significantly lower when discharges are driven by the droplets jet. While calculations with a three-dimensional electrostatic solver show that a local field enhancement near the droplets could help to explain these effects, a supplementary interpretation should be the extraction of electrons from the droplets surface by photons emitted from the positive streamer front.

Experimental Study of Electrohydrodynamic Induction Pumping of a Dielectric Micro Liquid Film in External Horizontal Condensation Process

Abstract: Electrohydrodynamic (EHD) induction pumping is based on charges induced in a dielectric liquid and delayed at a gradient or discontinuity of the electric conductivity. A traveling electric wave (AC) attracts or repels these induced charges, leading to liquid motion. EHD induction pumping of a dielectric micro condensation film, in an external horizontal configuration, is investigated experimentally. The pumping and its effect on heat transfer are explored by varying the voltage and frequency of the electric traveling wave, as well as the condensation heal flux. This study provides a fundamental understanding of induction pumping of micro liquid film and illustrates its potential for managing the flow and enhancing the heat transfer in the presence of phase change

Fast response wide viewing angle liquid crystal cell with double-side fringe-field switching

Abstract: A four-electrode liquid crystal cell, featuring a double-side fringe-field switching, has been designed with two-layer electrodes on both glass substrates. The two-layer electrode is the same as that used in fringe-field switching liquid crystal displays. Using a negative dielectric liquid crystal, a homogeneous cell has been fabricated with top and bottom stripe electrodes perpendicular to each other. The fringe fields near top and bottom surfaces drive the homogeneous liquid crystal layer to a twisted structure. The distributions of electric field and molecular director are obtained by theoretical analysis. The double-side fringe-field switching cell shows a much faster response and wider viewing cone compared to traditional fringe-field switching one. The improved electro-optical properties are due to the wider and more symmetric director distribution with respect to the midplane of the liquid crystal cell.

Flow visualization and image analysis of gas-phase AC corona discharge induced electrohydrodynamic liquid flow in a stratified fluid

Abstract: A phenomenon of AC gas-phase needle-plate corona discharge induced electrohydrodynamic (EHD) liquid flow in a stratified fluid has been investigated experimentally. The flow visualization of flow pattern is carried out by a fluorescent dielectric liquid tracer, where the steady EHD liquid motion induced by the corona discharge is presented in visual impressions. The results show that the EHD liquid flow direction on an electrode axis is not from needle to plate electrodes axis when the needle position was above the liquid layer. For the case of the needle electrode tip immersed into the dielectric liquid, it is well known that the dielectric liquid flows in anticlockwise rotation by contraries. The flow velocity distribution is experimentally obtained by a particle image velocimetry with image processing, where the measurement system takes sequential digital images of flow field illuminated by a laser light sheet for computed tomography. The mechanistic model based on interfacial momentum transfer effects on liquid-phase fluid motion is discussed in detail.

The effect of thermal relaxation time on a electrohydrodynamic viscoelastic fluid layer heated from below

Abstract: The problem of the onset of stability in a horizontal layer of a viscoelastic dielectric liquid with one relaxation time heated from below under the action of a vertical ac electric field is analyz...

Plasma treatment within dielectric fluids

Abstract: A dielectric liquid having entrained bubbles of gas or vapor is subjected to an electric field applied between spaced electrodes (112, 116) which generates microdischarges (and thus plasma) within the bubbles, allowing modification of the properties of the dielectric liquid The invention is particularly useful for treating hydrocarbon liquids such as gasolines and other liquid hydrocarbon fuels, which have extremely low dielectric constants Generating microdischarges within bubbles in such fuels can create compounds useful for higher combustion efficiency and/or lower emissions in internal combustion engines The invention may be directly implemented in an engine's fuel line upstream from the combustion chamber (eg, immediately prior to a fuel injector), thereby allowing the invention to be usefully implemented for fuel treatment prior to combustion

Dielectric spectroscopy characteristics of aged transformer oils

Abstract: Frequency domain dielectric spectroscopy, measurements of capacitance and dissipation factor/power factor in a wide frequency range becomes increasingly popular in assessment of power transformer insulation systems The interpretation of the measurement results is mostly made using a simple model taking the relative amount of oil and impregnated cellulose paper into account This paper presents main findings from frequency domain dielectric spectroscopy measurements on transformer oil samples from different power transformers still in service The interpretation model using oil permittivity of 22 combined with its conductivity is compared with actual measurements in the frequency range of 1000 Hz down to 001, sometimes down to 0001 Hz The temperature dependence and possible voltage dependence, especially at lower frequencies, are also investigated

Method for manufacturing semiconductor device and semiconductor device

Abstract: A method for manufacturing a semiconductor device includes the steps of forming a stress relief layer on a wafer such that the stress relief layer is away from at least part of electrodes formed on the wafer; forming a wiring layer in which lines that extend from the electrodes to the stress relief layer are formed; forming outer electrodes that are over the stress relief layer and are connected to the lines in the wiring layer; and forming a dielectric layer by applying dielectric liquid by an inkjet method to portions in the lines where the outer electrodes are connected to form a capacitor. The step of forming the dielectric layer is conducted after the step of forming the wiring layer.

Method and plant for the introduction of a liquid into a molten mass under pressure

Abstract: A method and plant (1) for the introduction of a liquid into a molten mass under pressure are described. Such a method and such a plant (1) are particularly but not exclusively suitable for the formation of a coating layer (5, 6, 7) on a cable element comprising at least one conductor (4), said layer (5, 6, 7) comprising an extruded thermoplastic polymer forming a continuous phase incorporating a dielectric liquid, and are useful, for example in the production of an electric cable (3) for the transportation and/or distribution of electrical power. The method comprises the steps of bringing the liquid to a predetermined pressure greater than the pressure of the molten mass; feeding the liquid into a plurality of storage tanks (12); and injecting the liquid into the molten mass at an injection pressure equal to the above-mentioned predetermined pressure by means of a plurality of injectors (13) in respective fluid communication with the plurality of storage tanks (12). Advantageously, this allows to accomplish a substantial continuity of delivery of the liquid in a technologically simple way and at low costs, while ensuring a dispersion as uniform as possible of the liquid within the molten mass.

Influence of the dielectrophoretic force on thermal convection

Abstract: The dielectrophoretic effect can be used to produce a buoyancy force in a fluid, since the dielectric strength of the fluid is a function of temperature. This effect is in many aspects similar to the gravitational force and can be used to investigate thermal flows in complex force fields. The strength of this buoyancy force is experimentally measured. The experimental results show that side effects, like flows induced by charge injection or chain formation of fluid molecules, can be avoided. Theory and experiment are in good agreement. For future applications, this set-up is a reliable test experiment to check the suitability of available fluids.

Modeling of electrowetted surface tension for addressable microfluidic systems: dominant physical effects, material dependences, and limiting phenomena

Abstract: This paper describes the equilibrium shape of a liquid drop under applied fields such as gravity and electrical fields, taking into account material properties such as dielectric constants, resistivities, and surface tension coefficients. The analysis is based on an energy minimization framework, scaling arguments, and on solutions of Maxwell's electrostatic equations. A rigorous and exact link is provided between the energy function corresponding to any given physical phenomena, and the resulting shape and size dependent force term in the (modified) Young's equation. It is shown that a dielectric solid and a perfectly conducting liquid is all that is needed to exactly recover the Young-Lippmann equation. A dielectric liquid on a conducting solid gives rise to line tension terms. Finally, a slightly resistive liquid on top of a dielectric, highly resistive solid gives rise to contact angle saturation and accurately predicts the experimental data that we observe in our electrowetting devices.

Dielectric fluid immersed MEMS tunable capacitors

Abstract: Enhancement of MEMS tunable capacitors using dielectric fluids is reported. Micromachined tunable capacitors were tested and characterized in air and in mineral oil with a relative permittivity (/spl epsi//sub r/) of 2.29. In oil the capacitors exhibit a factor of 2.2 to 2.29 increase in the initial capacitance as well as the achievable tuning range. The theoretical electrical and mechanical performance enhancements have been verified for capacitors with self-resonant frequencies of 18.3GHz in air. The high frequency testing device exhibited a capacitance of 344fF at 5GHz with a Q-factor of 72 in air, and a capacitance of 799fF with a Q-factor of 40 in oil. In addition, the devices immersed in oil have increased, tunable damping and a significantly higher breakdown voltage.

Tetherless neuromuscular disrupter gun with liquid-based capacitor (liquid dielectric)

Abstract: A neuromuscular disrupter gun and associated projectile. The projectile contains a capacitor, having its dielectric made from liquid. The gun charges the projectile prior to discharge from the gun of the projectile. The projectile holds the charge in flight and discharges on impact. To provide appropriate contact points, the projectile either carries contact wires or is designed to open and emit the liquid upon impact.

Method and device for monitoring moisture content of an immersed solid dielectric material

Abstract: A method and device (10) for monitoring moisture content level of a solid dielectric material (12), or paper, immersed in a dielectric fluid (14), or oil, both of which having respective moisture content, and known water solubility properties varying with temperature. The device (10) includes a moisture detector (22) and a temperature detector (20) for measuring moisture content level and temperature level of the oil (14), respectively. A microprocessor (24), electrically connected to both the moisture and the temperature detectors (22, 20), computes the moisture content level of the paper (12). The microprocessor (24) has the known water solubility properties of the paper (12) and the oil (14) stored therein and processes the oil moisture content level and the oil temperature level so as to determine the paper moisture content level. The latter being displayed on a display (26) connected to the microprocessor (24).

Liquid crystal added electrorheological fluid

Abstract: Electrorheological (ER) fluids are a class of materials whose rheological properties are controllable via the application of an external electric field. Without the presence of an electric field, the ER fluid exhibits Newtonian fluid behavior. However, when an electric field is applied to an ER fluid, its rheological response demonstrates Bingham characteristics. Since a typical ER fluid consists of a suspension of fine dielectric particles in a dielectric liquid, this ER behavior is considered to stem from polarization of the particles and the resultant structural change [1–3]. In order to obtain the polarization of the suspended particles, the dielectric constants of both the particles and the liquid medium must be different with the dielectric constant of the particles being typically higher than that of liquid. When an electric field is applied, a mutually interacting force occurs among these polarized particles, which form chains and aggregate to form thick columns bridging the two electrodes [4]. Increasing the ER effect is a natural way to improve the yield stress since the shear stress is related to the rate of change for the electric energy density with respect to the shear deformation. This rate of change depends mainly on the particle structures formed in an external electric field and the energy density of the ER fluids. When the structures are the same, the energy densities increase at a given electric field either by a increasing the mismatch between the dielectric constants of the particle and the carrier fluids or additives [5]. Although there exist reports of many particledispersed ER fluids, their practical utilization has been limited due to particle sedimentation, aggregation or solidification; particle or electrode abrasion; poor durability; and temperature dependence [6]. Low molar mass liquid crystals (LC) [7], lyotropic polymeric liquid crystals [8], and ferroelectric polymer solutions [9] have been proposed as alternative materials to resolve these problems. Compared to wet-base ER materials, in which the particles contain small amounts of moisture, various anhydrous systems, including zeolite [10] and conducting polymers such as polyaniline and its derivatives [11–14], poly(acene guinone) radicals [15], poly(p-phenylene) [16], polypyrrole [17], polymer/clay nanocomposites [18–20], and phosphate cellulose [21],

Charge packet evolution in paper-oil insulation and derived technological considerations

Abstract: Focused on the analysis of charge packet evolution in paper-oil insulation for DC cables application, the article tries to identify some parameters derived from PEA measurements, able to characterize accurately the phenomena associated with charge generation under certain poling conditions, but depending also on specific species mobility and local electric stress, consequent to the manufacturing process of the dielectric material.

Diagnostic of field aged cables and accessories by time-domain dielectric spectroscopy

Abstract: Dielectric Spectroscopy was used as a diagnostic tool to assess the degradation state of field-aged extruded cables retrieved from underground networks. A high voltage time-domain spectrometer was used to measure the time-domain dielectric response of unaged and field-aged cables up to 25 kV. In addition to time-domain dielectric spectroscopy (TDDS), high voltage frequency-domain dielectric spectroscopy (FDDS) was performed for the sake of comparison. Cables were characterized with respect to water content and water tree density. ACBD strength measurements were also performed on some of the cable samples in order to estimate their state of degradation. Field-aged and unaged cable accessories were also characterized with respect to their dielectric response in order to account for their effect on real line diagnostic.

Measurement equipment for investigation of the influence of viscosity of dielectric working fluids on spark erosion

Abstract: In this paper, measurement equipment for investigation of electrical discharges in dielectric working fluids is presented. Special features of these discharges are determined through a small distance between electrodes of 5 to 150 /spl mu/m and the ignition voltage up to 600 V. With the measuring system, a time-co-ordinated measurement of all electrical and optical processes of the discharging process can be accomplished. For using spark discharges is a machining process analyzing the influence of the viscosity of the work liquid on the ignition conditions is of great interest. Parameters measured at the plasma channel are starting parameters for a simulation of the thermal-affected zone of electrodes surfaces. The conditions for ignition and recovery strength of the work liquid are important characteristics for a machining process up to 4 million discharges per second.

An advanced model of a high pressure liquid dielectric switch for directed energy applications

Abstract: A high power liquid dielectric switch is being developed to satisfy the requirements for future directed energy applications. A flowing, high-pressure liquid dielectric was chosen for the design of a megavolt class switch operating at 100 pps. This paper reports on the modeling efforts commensurate with the design of a full size, prototype 250-300 kV concept validation test (CVT), switch that can transfer kilojoules per pulse. The flow system required to clear the discharge bubble and byproducts is intimately tied to the dynamics of energy deposition, and bubble formation. A circuit model has been developed to predict the discharge temporal characteristics including the voltage, current, risetime, arc energy deposition profile, and time varying arc inductance, bubble formation timescales and oscillatory bubble effects. The model utilizes both the Braginskii equation and Charlie Martin's equations to calculate the energy dissipated in the arc. A comparison of the two methods is presented. An integrated model also includes the hydrodynamic equations to predict the gas bubble volume and oscillation period, which are dramatically reduced with increasing pressure. Optimization studies indicate that a 1000-2000 psi switch appears to have ideal attributes including minimal dielectric flow requirements, compact size and low weight for implementation of a kilojoule, rep-rate switch.

Fluid dielectric variable capacitor

Abstract: This invention relates to an apparatus and method of using a high frequency, high power, fluid dielectric variable capacitor for an impedance matching network. The apparatus consists of a bow-tie rotary vane, a set of two fixed vanes, and a set of rotating vanes adapted to rotate interdigitally between the fixed vanes. A dielectric fluid is circulated between the fixed vanes and the rotating vanes for cooling the device. This arrangement facilitates production of a device having a higher capacitance and a smaller size, thus making it suitable for use in a matching network.

Voltage distortion effects on insulation systems behaviour in ASD motors

Abstract: Adopting PWM-like voltage waves, the insulation systems of stator windings of medium voltage motors have been characterized in presence and in absence of partial discharges. In addition, the dielectric losses increase for similar test samples, stressed both by a quasi square voltage and by a sinusoidal voltage, have been evaluated and reported.

Self Assembly of Polymer Structures Induced by Electric Field

Abstract: Amethod has been developed for fabricating polymer microstructures based on electric field induced self assembly and pattern formation. A dielectric fluid placed in between two conductive plates experience a force in an applied electric field gradient across the plates, which can induce a diffusive surface instability and self construction of the fluid surface. This process is exploited for the fabrication of self assembled polymer microstructures as well as replicated patterns through the use of pre-patterned plates or electrodes. FEM simulation is used to decide the minimum wavelength and electric gradient distribution of polymer structures. A variety of structures in the micron and nanometer scales including bio-fluidic MEMS, polymer optoelectronic devices can be fabricated using this method.

Dielectric measurements on HTS insulation systems for electric power equipment

Abstract: Since the development of flexible high temperature superconducting multifilament wires superconductive coils were constructed for the application in electric power equipment. The dielectric behaviour of conventional technology is well known, but this experience can only be partially applied to superconducting insulation systems. Some prototypes of cables, power and traction transformers and current limiters were built, but there is not sufficient knowledge about optimum dielectric structures and ageing. This paper gives a view to the criterions for liquid nitrogen as coolant and insulating medium of low temperature insulating systems for electric power equipment and shows the results of dielectric measurements tested with different structures.

Development of high power; high pressure, rep-rate, liquid dielectric switches

Abstract: The University of Missouri-Columbia (UMC) is developing high power liquid dielectric switches intended to address future high power microwave (HPM) applications Although requirements encompass a broad parameter space, the initial switch concept focuses on a 250-300kV output switch operated at 100 pps that will be scaled to 1MV Failure to clear high electric field regions prior to the next charge cycle results in prefires, thereby limiting the maximum achievable repetition rate Elevating the operating pressure, hence minimizing the bubble size and temporal properties, has alleviated this problem This paper presents the design philosophy, modeling, and experimental results obtained from a single shot prototype operated in oil at pressures ranging from atmospheric pressure to greater than 138 MPa (2000 psi)