Cathode Drop Research Articles

Experimental and modeling study of full- condition combustion characteristics of exhaust gas burners for solid oxide fuel cells

SOFC exhaust gas burner is an essential component of the SOFC thermal management system. The burner in the whole operating conditions of safe and stable combustion and smooth transition in the switching operating conditions is of great significance to the long-term and efficient operation of the SOFC power generation system. This paper builds an experimental test platform for the SOFC exhaust gas burner, tests the combustion performance of the burner in full operating conditions and operating conditions switching process, and establishes a prediction model for the combustion performance of SOFC exhaust gas burner by machine learning algorithm. The results show that the SOFC exhaust gas burner can meet the requirements of safe and stable combustion in all operating conditions and smooth transition between operating conditions; reliable combustion is achieved at the stable power generation condition with excess air factor of 7 ∼ 26, and the average cathode and anode pressure drop in the stable power generation condition is 142 Pa and 185 Pa, respectively; BP neural networks, support vector machines and random forests are used to establish a prediction model for the performance of the SOFC exhaust gas burner, and the random forests achieve the best prediction effect.

МОДЕЛЮВАННЯ ДУГОВОГО РОЗРЯДУ НА МІДНОМУ КАТОДІ ДЛЯ ГЕНЕРАЦІЇ НАНОСТРУКТУР

The paper considers the model of processes acting in the ionization layer of the cathode assembly during plasma generation of nanostructures. In the given model the processes in electrodynamic and gas - dynamic layers of plasma and their coordination are rather densely considered. Therefore, the solution of the model allows to adequately determine the magnitude of the cathode potential jump in the electrodynamic layer, which allows to compensate for all energy losses during the generation of nanostructures, and the magnitude of ion and electron fluxes at the cathode. The calculations were performed at a constant value of the elongation of the ionization layer, because it has little effect on the change in the ion current density along the length of the cathode layers. Also, the calculations confirmed a non-significant dependence of the initial pressure from the ionization layer on the temperature of the electrons. The obtained dependences, the fraction of ionic current at the cathode and the cathode potential drop from the current density at different cathode temperatures, showed that the change in the proportion of ionic current makes it possible to compensate for energy costs to maintain the cathode temperature. And consideration of the equation of energy balance allowed to establish the range of losses of the working fluid at which it is possible not to take into account the energy of evaporation of the working fluid and steam heating. To determine the current density at the cathode, the dependence of the thermoemission current on the cathode temperature and the dependence of the current density on the cathode on the plasma concentration at different cathode drops and different representations of electric field strengths were obtained. This allowed to determine the cathode temperature due to the ionic current density and to estimate the plasma concentration. Depending on the plasma concentration, the electric transfer coefficient for different emission mechanisms and cathode drops is obtained. All this allowed us to determine the dependence of the specific gravity leaving the cathode per unit time per unit area, on the cathode temperature and heat flux density for the copper cathode. Determining the specific gravity and the transfer coefficient makes it possible to determine the life of the cathode during plasma generation of nanostructures.

An Al and Cu layers with microporous deposited using pulsed arc spraying

The pulsed vacuum arc plasma have been using as media for spraying of copper and aluminum cathodes. The product of cathode erosion was deposited on the substrates made from crystalline silicon and stainless steel. A porous metal thick layers on the silicon substrate, that consist of spherical hollow particles were obtained. The continuous growing films and large particles on the metal surface as well as a number of cavities on the silicon surface were observed. The process of larger micron-sized particles formed from hundreds of nanoscale ones was observed. The difference of layer structure on surfaces can be explain that a morphology of the original surface affects the size of the deposited particles. The role of cathode drops and buffer plasma in deposition process discussed.

The Effect of Polarity and Hydrostatic Pressure on Operational Characteristics of Rutile Electrode in Underwater Welding.

In order to provide a better understanding of the phenomena that define the weld bead penetration and melting rate of consumables in underwater welding, welds were developed with a rutile electrode in air welding conditions and at the simulated depths of 5 and 10 m with the use of a hyperbaric chamber and a gravity feeding system. In this way, voltage and current signals were acquired. Data processing involved the welding voltage, determination of the sum of the anodic and cathodic drops, calculation of the short-circuit factor, and determination of the melting rate. Cross-sectional samples were also taken from the weld bead to assess bead geometry. As a result, the collected data show that the generation of energy in the arc–electrode connection in direct polarity (direct current electrode negative-DCEN) is affected by the hydrostatic pressure, causing a loss of fusion efficiency, a drop of operating voltage, decreased arc length, and increased number of short-circuit events. The combination of these characteristics kept the weld bead geometry unchanged, compared to dry weld conditions. With the positive electrode (direct current electrode positive-DCEP), radial losses were derived from greater arc lengths resulting from increasing hydrostatic pressure, which led to a decrease in weld penetration.

Optimal design of cathode flow channel for air-cooled PEMFC with open cathode

Air-cooled open-cathode low temperature proton exchange membrane fuel cell (AO-LTPEMFC) with low weight, small volume and compact system has become the new potential power source in the unmanned aerial vehicle (UAV). However, the desirable parameters of the cathode channel are a very important factor to influence the cell performance and the compact of the stack, which have the higher requirements put forward to the structural designs of the cathode channel of AO-LTPEMFC. Thus, some single AO-LTPEMFC fabricated with different width:0.9–1.5 mm, depth:1.1–1.5 mm, ratio (width/landing):1:0.7–1:1.3 and bending:0–10° of the cathode channel was investigated to optimize the cell performance and temperature distribution in the 2 mm plate and determine desirable design parameters. The results show that the different design parameters of the cathode channel affect the contact resistance, oxygen mass transfer of cathode and pressure drop in air flow. For AO-LTPEMFC, to keep the best performance, the cathode channel design parameters should be operated at appropriate width, as deep as possible, small ratio and bending. Through the comparison of various designs, combined with practice process, the optimum design size with width (1.1 mm) × depth (1.3 mm) × width/landing (1:0.7) × bending angel (θ) (5°) was obtained based on the 2 mm thickness of the bipolar plate, which could get the maximum performance and improve the compactness of system. Moreover, analysis in this study will provide a new guideline for the development of cathode flow field plate design in application.

Arc-cathode attachment in GMA welding

A model for arc-cathode attachment in gas metal arc welding is presented. It considers the cathodic heating in the case of a non-refractory iron cathode, with the assumption of the lowering of the local plasma temperature, due to cold metal vapor. It takes the plasma bulk temperature as well as the cathode drop voltage as free parameters and it gives a maximum of heat flux and current density for a cathode surface temperature below boiling temperature. The applicability as a heat source description in a weld pool simulation has been shown, and the temperature field of the cathode was calculated, giving rise to heat flux and current density distributions, which differ significantly from the converntionally used axisymmetric Gaussian distribution. The maximum cathode surface temperature was lower than boiling temperature, which is in agreement with the observeration.

IMPACT OF TRANSFER PROCESSES OF LIQIUD CATHODE COMPONENTS ON PHYSICAL-CHEMICAL PARAMETERS OF ATMOSPHERIC PRESSURE DC DISCHARGE

Experimental data on glow discharge parameters of atmospheric pressure in air with cathodes from distilled water and water containing ions of potassium, sodium and copper (II) are obtained. Chlorides of the corresponding salts were used. The current range was 20-60 mA, and the solution concentrations were -0.1-0.4 mol/l. The cathode drops of the potential and the electric fields in the plasma are determined by the mobile anode method. With emission spectroscopy by modeling the unresolved rotational structure of the emission bands of the second positive system of nitrogen molecules, gas temperatures were found. On the basis of these data, the total concentrations of the particles, the reduced electric field strengths, were found. It is found that the increase in the discharge current leads to a decrease in the cathode drops of the potential, the strengths of the electric fields, and the reduced field strengths. At the same time, the temperature of the gas was practically independent on the discharge current and it was 1600 ± 150 K. By numerical solution of the Boltzmann equation for electrons, electron energy distribution functions, mean energies and electron concentrations and rate constants of the processes occurring under the action of electron impact were determined. An estimate is made of the contribution to the formation of charged particles in the plasma of ionization processes of metal atoms that appear in the gas phase as a result of non-equilibrium transfer from the liquid cathode. It is shown that for molar fractions of metal atoms of 10-4 and higher, ionization is completely determined by collisions of electrons with metal atoms, rather than with molecules of the main plasma-forming gas. It is also shown that discharges with cathodes containing salt solutions have smaller values of cathode potential drops.Forcitation:Kuletsan A.L., Shutov D.A., Rybkin V.V. Impact of transfer processes of liqiud cathode components on physical-chemical parameters of atmospheric pressure dc discharge. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 6. P. 52-58.

Carbon black-derived graphene quantum dots composited with carbon aerogel as a highly efficient and stable reduction catalyst for the iodide/tri-iodide couple.

A microwave-assisted oxidative cleavage process is developed to prepare graphene quantum dots (GQDs) from carbon black. The size evolution of the resulting carbonaceous products is studied. In one hour, GQDs of a size less than 10 nm and thickness less than 2 nm are obtained. These GQDs are further composited with mesoporous carbon aerogels (CA) by a filtration process to form GQD-decorated CA composites (GQD/CA). The GQD/CA composite is applied as a catalyst electrode for the reduction of I3(-) to I(-), a critical electrolyte regeneration reaction in dye-sensitized solar cells (DSSCs). Also investigated are Pt electrodes, the expensive traditional counter electrode material for DSSCs, and plain CA electrodes for comparison. Based on data derived from cyclic voltammograms and Tafel plots, the GQD/CA composite exhibits catalytic efficiencies comparable to that of Pt electrodes and better than that of plain CA electrodes. The GQD/CA electrodes, however, surpass the Pt electrodes in terms of long-term stability. The cathodic current drops significantly after 500 cycles for the Pt and plain CA electrodes, whereas the cathodic current is slightly increased for the GQD/CA electrodes. The GQD/CA composite thus proves to be an inexpensive, efficient, and stable alternative to Pt as the counter electrode material for DSSCs.

Determination of the cathode and anode voltage drops in high power low-pressure amalgam lamps

For the first time, cathode and anode drops of powerful low-pressure amalgam lamps were measured. The lamp discharge current is 3.2 A, discharge current frequency is 43 kHz, linear electric power is 2.4 W/cm. The method of determination of a cathode drop is based on the change of a lamp operating voltage at variation of the electrode filament current at constant discharge current. The total (cathode plus anode) drop of voltage was measured by other, independent ways. The maximum cathode fall is 10.8 V; the anode fall corresponding to the maximal cathode fall is 2.4 V. It is shown that in powerful low pressure amalgam lamps the anode fall makes a considerable contribution (in certain cases, the basic one) to heating of electrodes. Therefore, the anode fall cannot be neglected, at design an electrode and ballast of amalgam lamps with operating discharge current frequency of tens of kHz.

The analytic calculation of ionization-drift waves (3D-Strata) of nanosecond discharges: The determination of the cathode drop in nanosecond discharges according to the number of visualized plasma structures

The values of the cathode drop (CD) are estimated in nanosecond discharges with a slot cathode in argon plasma to view the total number of strata in the discharge gap (n ∼ 10), and the dependence of the CD on the discharge parameters is studied. In the experiments, the structurization of a nanosecond discharge with a hollow cathode (stratum) in argon is analytically simulated by the author. It is proved that the strata in nanosecond discharges are caused by the drift of electrons and the direct ionization by the electron impact, thus, being ionization-drift waves. The drift removal of electrons leads to the formation of positively charged layers of the space charge, a significant increase of the role of the peripheral ionization, and the cumulation of electrons in the plasma focuses (similar to the Lagrange libration points discovered by Euler in 1769).

Kinetics of Formation of an Oxide Film on the Surface of the Cathode in an Atmospheric-Pressure Glow Discharge in Helium

The kinetics of formation of an oxide film on the surface of the cathode of an atmospheric-pressure glow discharge in helium has been investigated by the method of laser reflectometry. It has been established that the film is formed at a cathode temperature exceeding 550 K, and in 200 sec from the time of discharge initiation at a current of 1 A it becomes thicker than 1 μm. The film consists of several concentric zones. For each of these zones, a change in time of the directional hemispherical coefficient of reflection at a wavelength of 0.63 μm was determined. It is shown that the formation of an oxide film on the cathode surface leads to an increase in the cathode drop.

An approach to estimate the sputtering yield of water in glow-discharge electrolysis

When a high positive voltage is applied to the electrode above the negative liquid surface, glow-discharge is generated between the electrode and the liquid surface under reduced pressure. Bombardment of the water surface by energetic projectiles in glow-discharge electrolysis (GDE) leads to ejection of atoms and molecules from the water surface as Hickling reviews [1]. Although sputtering in GDE could be applied to film formation of oxide and diamond [2–4], virtually nothing is known about the sputtering yield of water. The collisional process occurs in the 100–1000 μm thick cathode sheath with a cathode drop of about 400 V [5]; the process increases the number of projectile by charge transfer [6]. The projectile energy distribution is likely to be very broad and even the average projectile energy is unknown under the typical GDE conditions. In our previous investigation, sputtering yield of water was deduced from the liquid loss assuming that the loss is totally due to the sputtering [7]. While, in the course of another experiment, we were obliged to admit that the water loss is due not only to the sputtering but also to the local heating of water and subsequent evaporation. How can we estimate the water loss due to sputtering excluding the effect of thermal evaporation? This work reports an approach to distinguish the sputtering from the thermal vaporization. Sputtering was carried out in a fused quartz glass chamber of 5 cm diameter as illustrated in Fig. 1. The positive electrode was a tungsten wire of 0.5 mm diameter. Water was biased negatively via graphite block. The electrode-liquid distance was 8 mm and the liquid layer thickness was 20 mm. The initial conductivity of distilled water was adjusted to about 60 μS/cm by adding a small amount of HCl. Prior to experiment, the water was evacuated for 1 h for degassing. Hydrogen gas was introduced in the chamber at a flow rate of 100 sccm. The pumped up water led to the surface water flow by overflowing the water into the reservoir. The circulation rate of the pump varied between 50 and 188 ml/min. The water loss was obtained from the difference in the water level in the measuring cylinder at 293 K under atmospheric pressure. First of all, the operational error and the amount of the evaporation at 293 K under 13 kPa (100 Torr) were evaluated. The operational error includes the error due to the thermal expansion of water. The water was circu-

Cathode Drop of the Potential of a Vacuum Arc of Metals

The basic mechanisms of ionization in the cathode spot of a vacuum arc are considered. It is shown that the singly charged positive ions formed here are a result of the collision ionization of the evaporated atoms of a metal by electrons. On this basis the assumption is made that the cathode drop of the potential of the vacuum arc of metals is determined by the energy of ionizing electrons at which the ionization section attains its maximum.

Spectropolarization investigations of the region of the cathode drop in the potential of a helium glow discharge at atmospheric pressure

The dimensions of the region of the cathode drop in potential in a helium glow discharge at atmospheric pressure (in Kiselevskii’s plasma source) are determined. Using Stark spectroscopy of the Balmer-series hydrogen line Hβ the spatial distribution of the constant and variable components of the electric-field strength is measured.

Nonself-sustained arc discharge in anode material vapors

The basic characteristics of the nonself-sustained arc discharge in a vapor of the anode material are studied. The influence of thermoemission parameters of the cathode on volt-ampere characteristics of the discharge is described. It is established that in a free mode of the discharge cathode operation, when the discharge current I/sub D/ is lower than the current of the thermoelectron emission from the discharge cathode I/sub C/, the deposition rate of the films q is directly proportional to the discharge current I/sub D/. In the compelled mode of the cathode operation, when I/sub D/>I/sub C/, q/spl sim/W/sub D//sup 2/, where W/sub D/=I/sub D/U/sub D/ with U/sub D/ being the discharge voltage. It is shown that the magnetic field increases the plasma density and changes the density profile from n(x)-1/x/sup 2/ to n(x)-1/x with x being a distance along the flow. The motion of created plasma flow is shown to have a noncollisional character with constant electron temperature of 5-7 eV along the flow. The values of plasma potential and electric field in the flow are determined; the values of cathodic and anodic potential drops in the discharge are evaluated. The angular distributions of ion and neutral fluxes in the created plasma flow are described. It is shown that the plasma flows parameters depend substantially on the working material. With use of crossed electric and magnetic fields, the flow ionization coefficient was enhanced up to 85% for the discharge in Ti vapors, and 35% for the discharge in Cu vapors.

Voltage of the vacuum arc with a ring anode in an axial magnetic field

The plasma jet focusing and voltage distribution in the interelectrode gap of a vacuum arc with a ring anode and subjected to an axial magnetic field were studied theoretically. A two-dimensional model was developed based on the free plasma jet expansion into vacuum, and the steady-state solution of the fully ionized plasma in the hydrodynamic approximation was analyzed. It was found that the imposition of an axial magnetic field reduces the radial expansion of the plasma jet. The characteristic jet angle decreases from about 40/spl deg/ in the zero magnetic field case and approaches a value of about 20/spl deg/ with a 0.02 T magnetic field. The arc voltage consisting of the cathode drop, the plasma voltage drop, and anode sheath drop increased, with the imposition of a magnetic field, and decreased with the anode length. The model was compared to experimental measurements of the vacuum arc voltage behavior in an axial magnetic field, and good agreement was found.

Critical parameters of the cathode region of a vacuum arc

An attempt has been made to determine the limiting values of the main physical parameters that define the current transfer process through the cathode spot plasma: current density, temperature, and the concentration of charge particles. The values obtained reveal the upper bound of these parameters. The evaluations are carried out on the basis of balance correlations and with consideration of the fact that conductivity of an ideal copper vapor plasma in the given range of temperature and concentrations is naturally more than that of a nonideal one. On the basis of the experimental and theoretical reasons discussed, it is concluded that there are two stages in the development of a nonstationary cathode spot, namely, the stage of initiation and the regular stage. During initiation, the current density achieves the values at which the explosion emission becomes possible while the cathode drop is up to 100-200 V. This stage lasts no longer than 1-3 ns. The medium providing the transport of current in the regular stage is generated mostly during the initiation stage. In the regular stage, which lasts 5-7 mu s in the case of a copper cathode, the cathode drop is about 15 V and no considerable erosion of cathode material occurs. The theoretical estimates verify the existence of the two stages in the development of a nonstationary cathode spot and demonstrate that there are some parameters that are critical from the viewpoint of whether the initiating on regular current density takes place. >

Improvement of a proposed model for heat conduction in an electrode submitted to an electric discharge: Application to the indirect determination of the anodic and cathodic voltage drops

We present an improved version of a heat-conduction model which leads to better-computed values of the anodic voltage drops for electric discharges in a liquid dielectric, with a short interelectrode gap (about 50 μm) and short duration (10–1000 μs). The results obtained show monotonic variations according to the duration of the discharge and peak current, and correspond to the measured value of the total interelectrode voltage drop.

A model for the cathode mechanism in low-current metal vapour arcs

An analytical model is proposed for the cathode spot of a metal vapour arc. A number of physical parameters at the cathode surface and at the boundary of the cathodic plasma such as macroscopic velocity, temperatures, fluxes, particle densities and electric field can be determined from equations for conservation of electric charge, mass, momentum and energy, the equation for ion current to the cathode, bipolar space charge equation, Saha equation, electron emission equation, and evaporation equation. The cathode drop voltage and the current density serve as independent variables. The multiply charged ions are taken into account, and the jumps of some quantities over the first mean free path-due to non-equilibrium evaporation-are incorporated into the model. Numerical calculations are carried out for low-current copper vacuum arcs. The results are compared with experimental data.

The production of large concentrations of molecular ions in the lengthened negative glow region of a discharge

A technique for enhancement of positive molecular ion concentrations in a glow discharge is presented. The technique consists of modifying an anomalous glow discharge by the addition of a longitudinal magnetic field of up to 300 G. Enhancements in the ion signal strength, as measured by millimeter and submillimeter wave spectroscopy, are approximately two orders of magnitude. Evidence is presented that the magnetic field increases the length of the ion rich negative glow by restricting inside a small diameter tube the ionizing electrons accelerated by the large cathode drop of an anomalous glow discharge.