Effect of Anode Dielectric Coating on Hall Thruster Operation

An interesting phenomenon observed in the near-anode region of a Hall thruster is that the anode fall changes from positive to negative upon removal of the dielectric coating, which is produced on the anode surface during the normal course of Hall thruster operation. The anode fall might affect the thruster lifetime and acceleration efficiency. The effect of the anode coating on the anode fall is studied experimentally using both biased and emissive probes. Measurements of discharge current oscillations indicate that thruster operation is more stable with the coated anode

Numerical Study of Heterogeneous Reactions in an SOFC Anode with Oxygen Addition

Previous experimental studies have shown that addition of small amounts of oxygen to a hydrocarbon fuel stream can control coking in the anode, while relatively large amounts of oxygen are present in the fuel stream in single-chamber solid oxide fuel cells (SOFCs). In order to rationally design an anode for such use, it is important to understand the coupled catalytic oxidation/reforming chemistry and diffusion within the anode under SOFC operating conditions. In this study, the heterogeneous catalytic reactions in the anode of an anode-supported SOFC running on methane fuel with added oxygen are numerically investigated using a model that accounts for catalytic chemistry, porous media transport, and electrochemistry at the anode/electrolyte interface. Using an experimentally validated heterogeneous reaction mechanism for methane partial oxidation and reforming on nickel, we identify three distinct reaction zones at different depths within the anode: a thin outer layer in which oxygen is nearly fully consumed in oxidizing methane and hydrogen, followed by a reforming region, and then a water–gas shift region deep within the anode. Both single-chamber and dual-chamber SOFC anodes are explored

DEVELOPMENT OF TINB2O7 ANODE FOR LITHIUM ION BATTERY ANODES

I have received 1200 dollars research scholarship.With an increase in gasoline price and greenhouse gas emissions, hybrid electrical vehicles (HEV) and pure electric vehicles (EV) have been commercialized in auto market. Li-ion batteries have become the dominant power source for the EV applications because of many advantages such as high energy densities, less pollution, stable performance and long cycle life. However, the market for HEVs and EVs need to overcome many technical issues. For example, energy densities and cycle life of Li-ion batteries need to be improved at low temperature for electrical vehicle applications. TiNb2O7 (TNO) electrode-based battery can be a good choice in order to improve the energy densities and cycle life. The original anode-based batteries are Li4Ti5O12 (LTO) anode-based batteries. I have made a comparison between TNO anode and LTO anode for Li-ion batteries. The energy densities of TNO anode-based batteries are around 350Wh/L and the energy densities of LTO anode-based batteries are around 177Wh/L. It means that TNO anode-based batteries have a higher energy density than LTO anode-based batteries. In addition, TNO anode batteries have a longer cycle life and shorter charging time than LTO anode batteries. The purpose of this research is to identify whether the TNO anodes-based batteries have the advantage of high energy and power densities for Li-ion batteries application. First, I need to identify whether the TNO anode can be run in normal cycling battery by doing half-cell test. I have done the half-cell test which consist of TNO anode and metallic Li as a counter electrode. The voltage profile obtained from half-cell test fits well with TNO electrode. In addition, cycle life tendency corresponding to high-density TNO composite electrode which indicate the TNO electrode can be used in normal cycling battery. In the future research study, I will identify the important parameters that lead to poor performance in the low-temperature condition and demonstrate the performance of TiNb2O7 anodes-based batteries has been improved in the low temperature condition.College of Engineering Research OfficeNo embargoAcademic Major: Mechanical Engineerin

Optimization of Plasma Plume Characteristics Based on Multi-anode Coaxial Ablative Pulsed Plasma Thruster

A special surface discharge is proposed based on the multi-anode electrode geometry. Instead of the traditional surface flashover of creepage on the insulator surface between the electrodes, a surface discharge with one of the electrodes being placed far away from the insulator is achieved in this paper. The unique electric field distribution due to the multi-anode electrode geometry has a significant influence on the discharge process of the surface discharge. It changes the generation and propagation process of the plasma, forming a plasma plume contributes to the propulsion performance of the thruster. Through theoretical analysis of the obtained plume data, it is indicated that the ablative pulsed plasma thruster based on multi-anode electrode geometry (short for multi-anode APPT) promotes the internal pressure of the plasma jet during its propagation and significantly increases the density and energy of charged particles. The discharge phenomena manifest that the multi-anode APPT and the helix-coil multi-anode APPT effectively increase the intensity of the plasma plume. Through electron density spatial distribution measurement, it has been found that the helix-coil multi-anode APPT increases the density of plasma in the axial direction to more than 4 times of the conventional coaxial APPT and reduces the electron density in other directions. In the propulsion test, it has been demonstrated that the multi-anode APPT and the helix-coil multi-anode APPT have better performance in terms of the impulse bit and the thrust-to-power ratio. In addition, it is also identified that the pinch effect will be enhanced with the increase of discharge power and the propulsion performance is promoted more distinctly. The multi-anode APPT and the helixcoil multi-anode APPT have been proved to have potential application advantage in the field of micro-satellite propulsion.Comment: 12 pages, 12 figure

Investigation of low current gas tungsten arc welding using split anode calorimetry

Most previous split anode calorimetry research has applied high weld currents which exhibit pseudo Gaussian distributions of arc current and power density. In this paper we investigate low current arcs and show that both the current and power distributions have minima in the centre – varying significantly from the expected Gaussian profile. This was postulated due to the formation of the arc with the copper anode and the tungsten cathode. Furthermore, a number of parameters were varied including the step size between measurements, anode thickness and anode surface condition as well as cathode type and tip geometry. The step size between measurements significantly influenced the distribution profile and the anode thickness needed to be above 7 mm to obtain consistent results

Coaxial anode wire for gas radiation counters

The design and characteristics of a gas radiation counter are discussed. The coaxial anode consists of an elongated central wire covered with an electrically insulating sleeve. Several longitudinally discontinuous segments of an electrically conductive coating are disposed about the insulating sleeve in a coaxial pattern along the length of the central wire. The conductive coating segments form a veto or rejection anode at each end of the central wire and a main or primary charge detecting anode between the ends. The segments are coupled together so that the primary charge detecting anode is connected to detection circuitry in anti-coincidence with the veto anodes. Background radiation detected by either of the veto anodes and the primary charge detecting anode is rejected and the sensitivity of the radiation counter device is increased

Coaxial anode improves sensitivity of gas radiation counters

Anode wire itself is enclosed by three segments. Two on ends are rejector segments, and middle one is primary charge-detecting segment. Anode wire is made from tungsten and is surrounded by enamel insulation. Enamel is covered by segments of vapor-deposited gold. At one point in center segment, gold layer makes direct contact with anode wire

The anode proximity effect for generic smooth field emitters

The proximity of the anode to a curved field electron emitter alters the electric field at the apex and its neighbourhood. A formula for the apex field enhancement factor, $\gamma_a(D)$, for generic smooth emitters is derived using the line charge model when the anode is at a distance $D$ from the cathode plane. The resulting approximately modular form is such that the anode proximity contribution can be calculated separately (using geometric quantities such as the anode-cathode distance $D$, the emitter height $h$ and the emitter apex radius of curvature $R_a$) and plugged into the expression for $\gamma_a(\infty)$. It is also shown that the variation of the enhancement factor on the surface of the emitter close to the apex is unaffected by the presence of the anode and continues to obey the generalized cosine law. These results are verified numerically for various generic emitter shapes using COMSOL Multiphysics. Finally, the theory is applied to explain experimental observations on the scaling behavior of the $I-V$ field emission curve.Comment: 10 pages, numerical verification added, references update