Large Electrode Gap Research Articles

Radiofrequency assisted hot air drying of corn kernels: Drying characteristics, uniformity, quality, and energy consumption

In order to clarify the applicability of radio frequency assisted hot air drying (RFHAD) for harvested cereals, the drying characteristics, quality, and energy consumption of RFHAD with various air temperatures (40 °C, 50 °C, 60 °C, 70 °C) and electrode gaps (90 mm, 100 mm, 110 mm, 120 mm) for corn kernels was investigated by comparing with these of hot air drying (HAD). Results showed that the temperature of corn kernels was higher than that of hot air during RFHAD, hot air mainly played a convective cooling role, and the cooling intensity enhanced with the decrease of air temperature or electrode gap. However, RFHAD inherited the non-uniform characteristic of RF heating, showing a higher temperature at the edges of corn samples, but it could be improved at higher or lower air temperatures than that at 40 °C and larger electrode gaps. The drying efficiency, color difference, and crack rate of corn kernels increased with the increase of air temperature or decrease of electrode gap. Especially, for corn kernels with similar temperature by RFHAD (50 °C air temperature, 100 mm electrode gap) and HAD (60 °C air temperature), the drying time of RFHAD was 25% shorter than that of HAD, meanwhile, the color difference and crack rate were at a smaller level. The energy consumption of RFHAD was reduced at small electrode gaps and high air temperatures since the drying time was significantly shorter than that of HAD. The results provide useful assistance for developing effective strategies for RFHAD of corn kernels.

Long‐Range Charge Carrier Transport in Planar Polymer Bulk‐Heterojunction Photovoltaic Cells

One‐dimensional scanning optical beam‐induced current (OBIC) measurements have been carried out on polymer bulk heterojunction (BHJ) photovoltaic cells with a planar, or lateral configuration. The planar P3HT:PCBM cells have parallel aluminum or gold electrodes that are 390 to 560 micrometers apart. When a focused laser beam is scanned across the electrode gap, photocurrent or photovoltage is recorded as a function of beam position along with the transmission of the excitation beam. Despite the large electrode gap size, cells with symmetric Al/Al electrodes exhibit significant photocurrent and photovoltage which are the highest at the electrode interfaces and null at the cell center. The OBIC in these large planar polymer BHJ cells is attributed to the metal/BHJ blend Schottky junction. The larger Schottky barrier of the Al/BHJ junction gives rise to a stronger OBIC response than the Au/BHJ junction. The photocurrent and photovoltage always have opposite signs and are antisymmetric about the cell center. In asymmetric Al/Au cells, the electrode work function difference contributes an additional built‐in field/potential drop and significantly modifies the photocurrent and photovoltage profiles. The depletion width of the Al/BHJ Schottky junction is 110–120 μm, while the minority electron diffusion length is determined to be 43.8 μm.

Extremely Large Polymer Light‐Emitting Electrochemical Cells with Concentric Circular Electrodes

AbstractPlanar polymer light‐emitting electrochemical cells (LECs) with concentric circle electrodes are demonstrated. With a fixed outer electrode radius of 6.8 mm, the inner electrode radius is varied from 1 to 3 mm. All cells can be activated with a 40 V bias at 360 K. The extremely large electrode gap size allows for time‐lapsed imaging of the in situ electrochemical p‐ and n‐doping processes. When the advancing p‐ and n‐doping fronts meet, a light‐emitting junction in the shape of a jagged ring is formed near the center of the electrode gap. Reversing bias polarity pushes the light‐emitting junction outward to near the negative electrode. It is possible to achieve a perfectly centered emitting junction by fine tuning the inner electrode radius. The sensitivity of junction position to relative electrode radius indicates the p‐ and n‐doping reactions are strongly coupled. The concentric circular electrode configuration offers a cross sectional view of an LEC‐based light‐emitting fiber. In any fiber shaped light‐emitting device, the inner and outer electrodes always differ in size. This electrode asymmetry should be considered and exploited to achieve optimal cell performance.

Performance evaluation of hydrogen permeation through pd/cu membrane at different plasma system conditions

The interest of hydrogen separation using palladium-based membranes has been raised due to their high permeability and selectivity. In this study, the performance of hydrogen permeation using dielectric barrier discharge (DBD) plasma in a microchannel plate reactor (MPR) was investigated. Pure hydrogen gas was injected into the MPR reactor at H2 flow rate of 0.1 L/min. The effect of plasma only, plasma-catalyst, plasma-heating, and the electrode gap distance (EGD) on the performance of H2 permeation through Pd-Cu membrane was experimentally analyzed. The results showed that these parameters have an important influence on hydrogen permeation through Pd-Cu membrane. Small amount of permeated hydrogen gas was observed in the sole DBD plasma experiments when plasma applied at ambient temperature. Furthermore, a significant enhancement of hydrogen permeation rate at high input power was registered in the plasma-catalyst experiment because of the plasma creates an increase in the surface gas temperature increased subsequently catalyst temperature which enhanced the catalytic material activity. The best hydrogen permeation rate was achieved in the plasma-heating experiment and electrode gap distance of 4.5 mm. Moreover, it was found that the electrode gap distance (EGD) has an important role in enhancing the hydrogen permeation under DBD plasma. Additionally, it was found that at large electrode gap distance (4.5 mm) has the long residence time which improved the hydrogen permeability and H2 permeation rate reach the maximum value of 102.7%. Also, it can be concluded that the DBD plasma should be used with catalyst and a suitable electrode gap distance.

Evaluation of spark discharge

Electric sparks can ignite fires, initiate explosions, shock humans. These discharges release energies through very complex dynamic processes. The effects of changing energy (capacitance and voltage) and electrode parameters on spark discharge characteristics are investigated. A multi-energy high-voltage ignition system is built. Results show that the spark discharge energy by voltage is more stable than changing the energy by capacitance. The breakdown characteristics of electrodes are revealed under different electrode parameters by the field strength distribution of the electrode. The energy utilization efficiency of large electrode gap is about 5.55% higher than that of small electrode gap.

Higher thrust-to-power with large electrode gap spacing electroaerodynamic devices for aircraft propulsion

Electroaerodynamic (EAD) devices, which produce a propulsive force in air by electrostatic acceleration, have been demonstrated as a method of propulsion for airplanes. However, achieving sufficient thrust-to-power is a significant challenge in developing EAD aircraft which are practical. Theory predicts that devices with larger inter-electrode gap spacing will enable higher thrust-to-power, but most experimental work has been limited to gap spacings of less than 80 mm. Those studies which have investigated spacings of greater than 100 mm have found results deviating from theory, with lower thrust-to-power than predicted. We performed experiments between 50 and 300 mm gap spacing and conclude that three effects explain the discrepancy: ‘leakage current’ from the electrodes to the surroundings, which does not produce thrust but increases measured electrical power; reverse corona emission from the collecting electrode, which reduces thrust and increases power; and the electric potential of the thruster relative to its surroundings, which affects both leakage current and reverse corona emission. Our results show that if these effects are accounted for, the existing EAD theory is correct without modification beyond its previous range of validity and is applicable to wire-to-cylinder EAD devices up to at least 300 mm gap spacing. We support our experimental results with two-dimensional numerical simulations, which show that the experimental current and thrust, including effects of leakage current, can be reproduced by computation with 12% error—an important step towards numerical design and optimization. By experimentally replicating equilibrium in-flight conditions, we measure thrust-to-power in the laboratory of up to 15 N kW−1 for large gap spacing thrusters at practically useful thrust levels. This is two to three times higher than current implementations with smaller gap spacings, suggesting that large gap spacing thrusters will be suitable for future EAD-propelled flight applications at thrust-to-power competitive with or exceeding conventional propulsion.

Enhanced actuation of nanocrystalline diamond microelectromechanical disk resonators with AlN layers

A great potential of the use of aluminum nitride (AlN) to enhance the actuation of nanocrystalline diamond (NCD) microelectromechanical system disk resonators is revealed. A disk resonator with a unimorph (AlN/NCD) structure is fabricated by depositing a c-axis oriented AlN on a capacitive NCD disk resonator. The unimorph resonator is piezoelectrically actuated with flexural whispering gallery modes with a relatively large electrode gap spacing, i.e., the spacing which is greater than 1 μm, although this is not possible for the capacitive NCD disk resonator. This result is explained by a finite element method simulation where the piezoelectric actuation turns out to be more effective than the capacitive actuation when the electrode gap spacing is >0.8 μm. The simulation also shows that the electrode gap spacing required for the capacitive actuation to be more effective than the piezoelectric actuation exponentially decreases when the resonator dimension is scaled down for higher frequency operations. Our study indicates that the use of AlN is promising to decrease impedance levels of NCD disk resonators especially for their higher frequency operations.

Effect of longitudinal electrode arrangement on EHD-induced heat transfer enhancement in a rectangular channel

In this study, heat transfer enhancement in a rectangular channel by electrohydrodynamics (EHD) is investigated. The numerical simulation deals with the effects of longitudinal position for single electrode, longitudinal arrangement for multiple electrodes, and electrode number with optimal longitudinal arrangement. A factor ξ defined as the ratio of average heat transfer coefficient with EHD to that without EHD is used to evaluate the level of EHD-induced heat transfer augmentation. The results show that the closer for the electrode to the inlet, the larger the ξ is. It is also found that there is a competition between the inlet-closed position requirement and large electrode gap requirement to determine the optimal longitudinal electrode arrangement. Based on this result, the design criterion for the optimal longitudinal electrode arrangement with given electrode number is proposed and justified. The results also show that as the electrode number exceeds a certain value (7 in the present paper), the ξ with the optimal electrode arrangement reaches a plateau; further increasing the electrode number only increases the power consumption but has no contribution to the heat transfer enhancement. The results indicated here are limited to the geometry and the parameter range used in the present study.

Atmospheric air diffuse array-needles dielectric barrier discharge excited by positive, negative, and bipolar nanosecond pulses in large electrode gap

In this paper, positive, negative, and bipolar nanosecond pulses are employed to generate stable and diffuse discharge plasma using array needles-plate electrode configuration at atmospheric pressure. A comparison study of discharge images, electrical characteristics, optical emission spectra, and plasma vibrational temperature and rotational temperatures in three pulsed polarity discharges is carried on under different discharge conditions. It is found that bipolar pulse is beneficial to the excitation of diffuse dielectric barrier discharge, which can generate a room temperature plasma with more homogeneous and higher discharge intensity compared with unipolar discharges. Under the condition of 6 mm electrode gap distance, 26 kV pulse peak voltage, and 150 Hz pulse repetition rate, the emission intensity of N2 (C3Πu → B3Πg) of the bipolar pulsed discharge is 4 times higher than the unipolar discharge (both positive and negative), while the plasma gas temperature is kept at 300 K, which is about 10–20 K lower than the unipolar discharge plasma.

General Potential-Current Model and Validation for Electrocoagulation

A model relating potential and current in continuous parallel plate iron electrocoagulation (EC) was developed for application in drinking water treatment. The general model can be applied to any EC parallel plate system relying only on geometric and tabulated input variables without the need of system-specific experimentally derived constants. For the theoretical model, the anode and cathode were vertically divided into n equipotential segments in a single pass, upflow, and adiabatic EC reactor. Potential and energy balances were simultaneously solved at each vertical segment, which included the contribution of ionic concentrations, solution temperature and conductivity, cathodic hydrogen flux, and gas/liquid ratio. We experimentally validated the numerical model with a vertical upflow EC reactor using a 24cm height 99.99% pure iron anode divided into twelve 2cm segments. Individual experimental currents from each segment were summed to determine total current, and compared with the theoretically derived value. Several key variables were studied to determine their impact on model accuracy: solute type, solute concentration, current density, flow rate, inter-electrode gap, and electrode surface condition. Model results were in good agreement with experimental values at cell potentials of 2-20V (corresponding to a current density range of approximately 50-800 A/m2), with mean relative deviation of 9% for low flow rate, narrow electrode gap, polished electrodes, and 150mg/L NaCl. Highest deviation occurred with a large electrode gap, unpolished electrodes, and Na2SO4 electrolyte, due to parasitic H2O oxidation and less than unity current efficiency. This is the first general model which can be applied to any parallel plate EC system for accurate electrochemical voltage or current prediction.

Electron bounce resonance heating in dual-frequency capacitively coupled oxygen discharges

The electron bounce resonance heating (BRH) in dual-frequency capacitively coupled plasmas operated in oxygen is studied by different experimental methods and a particle-in-cell/Monte Carlo collision (PIC/MCC) simulation, and compared with the electropositive argon discharge. In comparison with argon, the experimental results show that in an oxygen discharge the resonance peaks in positive-ion density and light intensity tend to occur at larger electrode gaps. Moreover, at electrode gaps L > 2.5 cm, the positive-ion (and electron) density and the light emission drop monotonically in the oxygen discharge upon increasing L, whereas they rise (after an initial drop) in the argon case. At resonance gap the electronegativity reaches its maximum due to the BRH. All these experimental observations are explained by PIC/MCC simulations, which show that in the oxygen discharge the bulk electric field becomes quite strong and is out of phase with the sheath field. Therefore, it retards the resonance electrons when traversing the bulk, resulting in a suppressed BRH. Both experiment and simulation results show that this effect becomes more pronounced at lower high-frequency power, when the discharge mode changes from electropositive to electronegative. In a pure oxygen discharge, the BRH is suppressed with increasing pressure and almost diminishes at 12 Pa. Finally, the driving frequency significantly affects the BRH, because it determines the phase relation between bulk electric field and sheath electric field.

Quantitative Analysis of Electroplated Nickel Coating on Hard Metal

Electroplated nickel coating on cemented carbide is a potential pretreatment technique for providing an interlayer prior to diamond deposition on the hard metal substrate. The electroplated nickel coating is expected to be of high quality, for example, indicated by having adequate thickness and uniformity. Electroplating parameters should be set accordingly for this purpose. In this study, the gap distances between the electrodes and duration of electroplating process are the investigated variables. Their effect on the coating thickness and uniformity was analyzed and quantified using design of experiment. The nickel deposition was carried out by electroplating in a standard Watt's solution keeping other plating parameters (current: 0.1 Amp, electric potential: 1.0 V, and pH: 3.5) constant. The gap distance between anode and cathode varied at 5, 10, and 15 mm, while the plating time was 10, 20, and 30 minutes. Coating thickness was found to be proportional to the plating time and inversely proportional to the electrode gap distance, while the uniformity tends to improve at a large electrode gap. Empirical models of both coating thickness and uniformity were developed within the ranges of the gap distance and plating time settings, and an optimized solution was determined using these models.

Effect of bulk electric field reversal on the bounce resonance heating in dual-frequency capacitively coupled electronegative plasmas

The electron bounce resonance heating (BRH) in dual-frequency capacitively coupled plasmas operated in oxygen and argon has been studied by different experimental methods. In comparison with the electropositive argon discharge, the BRH in an electronegative discharge occurs at larger electrode gaps. Kinetic particle simulations reveal that in the oxygen discharge, the bulk electric field becomes quite strong and is out of phase with the sheath field. Therefore, it retards the resonant electrons when traversing the bulk, resulting in a suppressed BRH. This effect becomes more pronounced at lower high-frequency power, when the discharge mode changes from electropositive to electronegative.

Experimental study of a planar atmospheric-pressure plasma operating in the microplasma regime

Electrical characterization of a nonthermal radio-frequency atmospheric-pressure microplasma in a parallel plate configuration has shown that reducing electrode gap into the submillimeter range increases current and power density at a reduced voltage as compared to similar plasmas at larger electrode gaps which have no gap dependence. Calculation of sheath thickness and electric fields in the sheath and in the bulk demonstrate a dependence on the electrode gap as it is reduced into the submillimeter regime, indicating a distinct regime of operation.

Numerical simulation for welding pool and welding arc with variable active element and welding parameters

A numerical modelling of the welding arc and weld pool is established for moving argon shielded gas tungsten arc welding to systematically investigate the effect of the active element oxygen and the welding parameters on the Marangoni convection and the weld shape using FLUENT software. The different welding parameters will change the temperature distribution and gradient on the pool surface, and affect the strength of Marangoni convection and the weld shape. Under high oxygen content, the weld depth/width (D/W) ratio substantially depends on the welding parameters. A high welding speed or large electrode gap (arc length) will make the weld D/W ratio decrease. The weld D/W ratio initially increases and then remains constant around 0·5 with the increasing welding current. When the oxygen content is lower, the weld D/W ratio decreases with the increasing welding current. However, the weld D/W ratio is not sensitive to the welding speed or electrode gap. The predicted weld D/W ratio agrees well with the experimental results.

A new method for generation of synchronised capacitive sparks of low energy

Conventional tests for investigating the minimum ignition energy (MIE) of dust clouds are restricted to energies above a few mJ, due to the challenges of producing sparks of very low energies that can be synchronised with a transient dust cloud. In this paper, a new circuit for generating capacitive sparks of significantly lower energies than 1 mJ is presented. A measurement system for capturing voltage and current waveforms has been integrated in the circuit, offering the energy delivered to the spark by integration of the power-versus-time curve. When working with such low energy discharges, which are highly transient phenomena, attention must be paid to the measurement technique and methods of noise reduction in the measurement instruments. The measured spark energies range from 0.03 to 7 mJ, and they were found to constitute between 60 and 90 per cent of the energy stored on the discharge capacitors prior to breakdown. Losses to the measurement resistors are increasingly significant at higher energies and larger electrode gaps, due to the relatively large currents, and correspondingly small spark resistances. A simple circuit simulation, in which the spark conductivity is assumed proportional to the spark energy, offers voltage and current waveforms in good agreement with the measured ones, indicating that the spark is mainly resistive. In addition, the discharge channel's ability to carry current depends strongly on the supplied energy. The proportionality factor is found to depend on the breakdown voltage.

Langmuir Probe Measurement of Cesium Plasma in Thermionic Energy Converter

In order to determine the optimum conditions for thermionic energy converter (TEC) operation, a Langmuir probe has been applied to investigate a cesium plasma in a TEC operating in an unignited mode, which has a large electrode gap, and is operating at a relatively low emitter temperature. In the analysis of the probe characteristics, the work functions of and the electron emission from the emitter, collector and probe have been taken into account. It is confirmed by the present experiment that the floating and emitter sheath potentials estimated using parameters such as the electrode and probe work functions, thermionic emission current density and ion current density, produced by surface ionization together with measured electron and ion saturation currents, are in good agreement with those analyzed from the measured probe characteristics. Moreover, it is verified that the space-charge neutrality near the emitter affects the plasma density in the space between two electrodes more significantly than the thermionic electron current from the emitter. This leads to the conclusion that the relaxation of the negative space potential by the effective auxiliary discharge is important for the improvement of TEC output characteristics.

Physiological Features of Visceral Smooth Muscle Cells, With Special Reference to Receptors and Ion Channels

Visceral smooth muscle cells (VSMC) play an essential role, through changes in their contraction-relaxation cycle, in the maintenance of homeostasis in biological systems. The features of these cells differ markedly by tissue and by species; moreover, there are often regional differences within a given tissue. The biophysical features used to investigate ion channels in VSMC have progressed from the original extracellular recording methods (large electrode, single or double sucrose gap methods), to the intracellular (microelectrode) recording method, and then to methods for recording from membrane fractions (patch-clamp, including cell-attached patch-clamp, methods). Remarkable advances are now being made thanks to the application of these more modern biophysical procedures and to the development of techniques in molecular biology. Even so, we still have much to learn about the physiological features of these channels and about their contribution to the activity of both cell and tissue. In this review, we take a detailed look at ion channels in VSMC and at receptor-operated ion channels in particular; we look at their interaction with the contraction-relaxation cycle in individual VSMC and especially at the way in which their activity is related to Ca2+ movements and Ca2+ homeostasis in the cell. In sections II and III, we discuss research findings mainly derived from the use of the microelectrode, although we also introduce work done using the patch-clamp procedure. These sections cover work on the electrical activity of VSMC membranes (sect. II) and on neuromuscular transmission (sect. III). In sections IV and V, we discuss work done, using the patch-clamp procedure, on individual ion channels (Na+, Ca2+, K+, and Cl-; sect. IV) and on various types of receptor-operated ion channels (with or without coupled GTP-binding proteins and voltage dependent and independent; sect. V). In sect. VI, we look at work done on the role of Ca2+ in VSMC using the patch-clamp procedure, biochemical procedures, measurements of Ca2+ transients, and Ca2+ sensitivity of contractile proteins of VSMC. We discuss the way in which Ca2+ mobilization occurs after membrane activation (Ca2+ influx and efflux through the surface membrane, Ca2+ release from and uptake into the sarcoplasmic reticulum, and dynamic changes in Ca2+ within the cytosol). In this article, we make only limited reference to vascular smooth muscle research, since we reviewed the features of ion channels in vascular tissues only recently.

軌道分離・非磁場型質量分析計の試作

A new mass spectrometer of non-magnetic type which was proposed previously by the author (ref. 1), was examined experimentally. One of the anticipation in the preceding article is that the resolving power of the mass spectrometer increases in proportion to the transit time of the detecting ions in the rf field. To confirm this property experimentally, two types of the mass spectrometer tube were prepared. The first tube was prepared to examine the property that the resolving power is proportional to the recoiling number N of the motion of ions. The case of N=1 to 3 was studied with a demountable ion collector. The other test tube (N=2) was designed to have the large electrode gap of d2 (>d1). With the second tube, a factor of 1.5 increase in the resolving power over the conventional tube (d1=d2) will be obtained. The resolving power obtained with two types of the mass spectrometer showed good agreement with theoretically estimated values, respectively.This mass spectrometer is able to operate with frequency sweep method, and the relative transmission probability (relative ion current vs. mass to charge ratio) will be independent of the ion's mass. The result obtained showed constant ion transmission probability in the mass range larger than m/z=40, but it was decreased in the smaller mass range. The reduction is caused by the large rise time of the rf pulse used here. It was also confirmed experimentally that the resolving power does not be affected by the velocity distribution of beam ions.

Excitation of an atmospheric-pressure CO<inf>2</inf>-N<inf>2</inf>-He laser by capacitor discharges

The design of a new type of atmospheric pressure CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -He laser capable of producing 1.2-J infrared light pulses with a peak power of 0.5 MW is described. An investigation of the laser output dependence on gas flow, gas mixture, capacitor voltage, output coupling reflectivity, and electrode spacing was made. It is shown that even greater energies and powers should be possible at higher voltages and larger electrode gaps.