Dissertations / Theses on the topic 'Faradic current'

Electrical systems have become ubiquitous, and with them come the need to accurately monitor electric current. The aerospace industry is no exception. Modern aircraft may contain more than one hundred current sensors, each one critical to a properly functioning vehicle. While these sensors function acceptably, several areas have been identified for improvement: size, weight, and cost. Each sensor is bulky, taking up valuable space. They are also costly to manufacture. The existing design is based on the Hall effect, and has remained fundamentally unchanged for decades. With the recent progress in manufacturing techniques and materials, it would be beneficial to reexamine these sensors and determine if improvements can be made using the accomplishments of recent years. Of particular interest are microelectromechanical systems, also known as MEMS. Using a sensor based on MEMS technologies in which design, function, and fabrication are closely intertwined would automatically meet two of the three goals: reducing size and weight. MEMS additionally have the potential to allow existing systems to be miniaturized. Also of interest are advanced materials, some of which can behave as transducers, linking different physical phenomenon. The goal of this dissertation is to use advances in manufacturing techniques and materials, specifically those discussed above, to design a better current sensor. As part of this goal, several potential solutions were studied and optimized. Finally, proof-of-concept prototypes were fabricated and tested to validate the feasibility of the designs and offer insight into continued sensor development.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008.
Committee Co-Chair: Dr. Jianmin Qu; Committee Co-Chair: Dr. Mohammed Cherkaoui; Committee Member: Dr. Christophe Giraud-Audine; Committee Member: Dr. Nico Declercq. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.
"Spetember 2004."
Includes bibliographical references.
(cont.) above atmospheric pressure caused both positive current and negative current pulses with the negative pulse larger than the positive pulse. A pressure decrease of more than 10psi below atmospheric pressure also caused both positive current and negative current pulses with the positive current larger than the negative current pulse. Experiments showed that the negative current was generated by the galvanic action between the two dissimilar metals in the triaxial connector connecting the center electrode of the electrode chamber with the electrometer, as water condensed. Positive current could have been produced by the evaporation of moisture from the center electrode of the electrode chamber. Dew point analysis is performed to show that for water to condense on metallic surfaces, it is not necessary to reach the dew point. The calculated dew point temperature is lower than the temperature at which the water condenses upon the electrode surfaces. In the liquid and solid dielectric experiments, we use a patented Faraday cage which is composed of two identical in-line hollow, gold-plated Faraday cup electrodes that enclose the samples which move between them during each measurement under computer control. We conducted charge measurements using various electrometers to rule out the possibility of false instrument readings due to input offset voltage and other experimental effects. One wire mesh style of Faraday cage connected with an electrometer was also used to measure the charge. The liquid dielectrics are distilled water, tap water, Sargasso Sea water ...
This thesis is devoted to Faraday cage measurements of air, liquid, and solid dielectrics. Experiments use pressurized air with fixed Faraday cage electrodes, and a moving sample of liquid and solid dielectrics between two Faraday cup electrodes. Extensive experiments were conducted to understand the source of the unpredictable net measured charge. In the air experiment, the Faraday cage consists of a hollow, cylindrical, gold-plated brass electrode mounted within a gold-plated brass hermetic chamber that connects with earth ground. Measurements of transient current at various temperatures and humidity during transient air pressure change are presented. The flow of electrode current is shown not to be due to capacitance and input offset voltage changes, since the calculated value is on the order of 10⁻¹⁶ Amperes which is much less than the measured currents of order 10⁻¹³ Amperes. By controlling the internal relative humidity of air in the Faraday cage, and from the measurements of current using dry nitrogen, we confirm that the absence of moisture causes no current to flow. Amplitude of the measured current is found to be dependent upon the internal relative humidity. Repeatedly, polarity reversals were observed to occur, in part due to galvanic action between dissimilar metals as water condensed upon the insulating surface between them. At a low temperature with a small pressure change, only one pulse of current was observed to occur but, with a pressure change of more than l0psi, two opposite polarity pulses of current were shown to occur almost simultaneously. A small pressure increase only caused a pulse of negative current, and a small pressure decrease only caused a pulse of positive current. A pressure increase of more than l0psi
by M. Shahrooz Amin.
S.M.

Les procédés électrochimiques présentent beaucoup d’avantages dans le domaine du traitement et de la récupération de matière d’effluents industriels. Cependant, dans le cas de solutions diluées en ions métalliques, les électrodes classiques sont fortement limitées par leur efficacité ainsi que par leur taille. Dès lors, les électrodes poreuses, de par leur surface spécifique importante et de par leur structure particulière qui améliore le transport de matière et donc l’efficacité de l’électrode, représentent une alternative très intéressante aux électrodes classiques.

Parmi les électrodes poreuses, celles constituées de fibres métalliques semblent les plus prometteuses. L’objectif de ce travail est de donner les relations utiles pour dimensionner une cellule contenant ce type d’électrodes en vue du traitement d’effluents industriels contenant des ions métalliques.

Les électrodes étudiées ont été caractérisées par différentes techniques :microscopie électronique, méthode électrochimique, mesure de la perte de charge, conductimétrie, porosimétrie,… Cette caractérisation a permis de connaître la porosité, les surfaces spécifiques (géométrique, dynamique et électrochimique) et la tortuosité des électrodes.

Ensuite, le coefficient de transport de matière moyen a été étudié par une nouvelle méthode basée sur la mesure d’un rendement électrochimique. Cette méthode présente l’avantage de pouvoir travailler avec des vitesses de circulation de l’électrolyte compatibles avec celles utilisées industriellement. Pour cela, une cellule d’électrolyse à circulation forcée a été mise au point.

Afin de comprendre comment la géométrie d’une électrode poreuse de ce type influence le transport de matière local et la densité de courant et donc l’efficacité de l’électrode, le transport de matière et la densité de courant locale ont été modélisés autour d’un cylindre (représentatif d’une fibre) et validés par des mesures expérimentales. La modélisation s’est ensuite étendue à un réseau de fibres cylindriques représentatif des électrodes poreuses étudiées. Cette modélisation a permis d’obtenir une relation générale liant les nombres de Sherwood, de Reynolds et de Schmidt à des nombres sans dimension caractérisant la géométrie du réseau de fibres. Cette relation donne des résultats concordants avec ceux obtenus expérimentalement pour les électrodes poreuses étudiées.

Le volume utile d’une électrode poreuse dépend fortement des conditions expérimentales (concentration de l’électrolyte, vitesse de circulation, intensité du courant appliquée,…) et de la structure de l’électrode (porosité, surface spécifique,…). Ces paramètres influencent la distribution du potentiel et de la densité de courant dans l’électrode. Différents modèles de distribution sont comparés et appliqués aux électrodes poreuses étudiées. Cette distribution de courant influence le colmatage progressif de l’électrode poreuse en cours d’électrolyse. Il s’avère que l’électrode en contrôle diffusionnel (avec un rendement électrochimique faible) optimise la distribution du courant dans l’électrode et, de ce fait, ralenti son colmatage. De plus, travailler avec une solution diluée et une vitesse de circulation de l’électrolyte importante améliore la distribution du courant. Il en est de même si l’électrode poreuse présente une grande porosité et une faible surface spécifique.

Ce travail aura donc permis de proposer des relations indispensables pour le dimensionnement d’une cellule à électrodes poreuses (constituées de fibres métalliques) ainsi que les conditions opératoires idéales dans le cas du traitement d’effluents industriels contenant des ions métalliques./

Electrochemical techniques offer many advantages for the prevention of pollution problems in the industrial processes. However, flat electrodes are not ideal to treat dilute solutions containing metallic ions. With their high specific surface and open structure, which enhance mass transfer, porous electrodes are a good alternative for the treatment this kind of effluent. Fibre materials are particularly well suited as material for the production of porous electrodes.

The aim of this thesis is to study an electrochemical cell with a porous electrode in order to treat dilute metallic ions solutions and to provide dimensionless equations suited to scale-up the electrode for industrial application.

The porous electrodes, used in this thesis, are made of a stainless steel fibre network. The main properties and characteristics of these electrodes are studied by means of several techniques :electron microscopy, electrochemical methods (voltammetry, limiting current density measurerment), conductivity measurement, porosimetry, pressure drop measurement,… The obtained parameters are :porosity, specific surfaces (geometric, dynamic and electrochemical), fibres' diameter, tortuosity and the geometric disposition of the fibres in the electrodes. Mass transfer inside the porous electrodes is studied experimentally by a new developed method, linked to the measurement of the faradic yield as a function of different electrolysis parameters. For these measurements, an experimental electrolysis cell with high electrolyte flow rate has been designed and builds.

To understand how the geometry of the porous electrode influences the local and mean mass transfer coefficients and current densities, numerical studies and simulations have been performed.

The first type of simulation deals with a single wire (representative of a fibre from the porous electrode).

The second type of simulation deals with the integration of individual fibres in a fibre network. A correlation between dimensionless numbers such as Sherwood's, Reynolds' and Schmidt's numbers together with numbers characteristic of the electrode’s geometry has been established for Reynolds’s numbers ranging from 0,02 to 1,4. A good agreement between simulation and experimental measurements of mass transfer is observed.

The real effective electrochemical volume of the porous electrode depends on experimental conditions (current, concentration, flow velocity…) and electrode’s geometry (porosity, specific surface,…). These parameters influence the potential and current distribution inside the porous electrode. Several models of current distribution are applied to these electrodes and the theoretical simulations are compared with experimental measures.

As a result of these simulations, an electrode under diffusion control with a small faradic yield appears to be the best choice in order to homogenise the current density inside the porous electrodes. Dilute solutions, high flow velocity and electrodes with high porosity improve also the current density penetration inside the electrode. These observations are confirmed by an electrode’s plugging study.

In conclusion, this thesis provides mathematical relationships to scale-up a cell with porous electrodes of metallic fibre, and provides guidelines to treat, in an efficient manner industrial effluents containing metallic ions.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

In the presented work, an optical device for measuring current is proposed. It consists of a polarimeter, indicator and input device. Its work is based on the functional dependence of changes in the parameters of polarized light in the polarimeter from the current values that are being measured. The proposed current meter allows to reduce the dimensions and weight of the structure, as well as to increase the measurement accuracy.
В представленій роботі запропоновано оптичний пристрій для вимірювання струму. Він складається з поляриметра, індикатора та вхідного пристрою. В основу його роботи покладено функціональна залежність зміни параметрів поляризованого світла в поляриметрі від значень струму, що вимірюються. Запропонований вимірювач струму дає можливість зменшити габарити та масу конструкції, а також підвищити точність вимірювань.

Optical current sensors (OCSs) are initially developed to measure relatively large current over a wide range of frequency band. They are also used as protective devices in the event a fault occurs due to a short circuit, in the power generation and distribution industries. The basic principal used in OCS is the Faraday effect. When a light guiding faraday medium is placed in a magnetic field which is produced by the current flowing in the conductor around the magnetic core, the plane of polarization of the linearly polarized light is rotated. The angle of rotation is proportional to the magnetic field strength, proportionality constant and the interaction length. The proportionality constant is the Verdet constant V (λ, T), which is dependent on both temperature and wavelength of the light. Opto electrical methods are used to measure the angle of rotation of the polarization plane. By measuring the angle the current flowing in the current carrying conductor can be calculated. But the accuracy of the OCS is lost of the angle of rotation of the polarization plane is dependent on the Verdet constant, apart from the magnetic field strength. As temperature increases the Verdet constant decreases, so the angle of rotation decreases. To compensate the effect of temperature on the OCS, a new method has been proposed. The current and temperature are measured with the help of a duel frequency method. To detect the line current in the conductor or coil, a small signal from the line current is fed to the reference of the lock in. To detect the temperature, the coil is excited with an electrical signal of a frequency different from the line frequency, and a small sample of this frequency signal is applied to the reference of the lock in. The temperature and current readings obtained are look up at the database value to give the actual output. Controlled environment is maintained to record the values in the database that maps the current and temperature magnitude values at the DSP lock in amplifier, to the actual temperature and current. By this method we can achieve better compensation to the temperature changes, with a large dynamic range and better sensitivity and accuracy.

ABSTRACT CuZn Alloy- Based Electrocatalyst for CO2 Reduction Amira Alazmi Carbon dioxide (CO2) is one of the major greenhouse gases and its emission is a significant threat to global economy and sustainability. Efficient CO2 conversion leads to utilization of CO2 as a carbon feedstock, but activating the most stable carbon-based molecule, CO2, is a challenging task. Electrochemical conversion of CO2 is considered to be the beneficial approach to generate carbon-containing fuels directly from CO2, especially when the electronic energy is derived from renewable energies, such as solar, wind, geo-thermal and tidal. To achieve this goal, the development of an efficient electrocatalyst for CO2 reduction is essential. In this thesis, studies on CuZn alloys with heat treatments at different temperatures have been evaluated as electrocatalysts for CO2 reduction. It was found that the catalytic activity of these electrodes was strongly dependent on the thermal oxidation temperature before their use for electrochemical measurements. The polycrystalline CuZn electrode without thermal treatment shows the Faradaic efficiency for CO formation of only 30% at applied potential ~−1.0 V vs. RHE with current density of ~−2.55 mA cm−2. In contrast, the reduction of oxide-based CuZn alloy electrode exhibits 65% Faradaic efficiency for CO at lower applied potential about −1.0 V vs. RHE with current density of −2.55 mA cm−2. Furthermore, stable activity was achieved over several hours of the reduction reaction at the modified electrodes. Based on electrokinetic studies, this improvement could be attributed to further stabilization of the CO2•− on the oxide-based Cu-Zn alloy surface.

碩士
國立高雄師範大學
光電與通訊工程學系
105
We have presented an optical fiber current sensor based on a resonation cavity that is constructed by Faraday rotation mirrors. The Y-type resonation cavity has been proposed for response gain enhancement of the optical fiber current sensor. Three type of resonation cavity, different winding direction of sensing fiber and various amount of sensing heads has been investigated for analyses of sensor responses. 　　The optimal trade-off between power loss and rotation angle of the state of polarization can be obtained by a 3dB coupling ratio of the resonation cavity. The Y-type resonation cavity used in the optical fiber current sensor has obtained the improvement of the response gain but not achieved the prediction results due to the power loss of the fiber components.

碩士
國立清華大學
電機工程研究所
81
In this thesis we use a statistical model to discuss the effect of downlead on a fiber-optic Faraday current sensor. The impact of environmental disturbance induced in the down- lead is analyzed under a certain specified cases of component misalignment.The mean and the standard deviation of the sensor output are calculated for various strengths of disturbance. Numerical results show that the sensor output can be quite different from the expected due to the aforementioned effect of downlead.