Coaxial Cylindrical Electrodes Research Articles

Electromagnetically driven flow in unsupported electrolyte layers: lubrication theory and linear stability of annular flow

We consider a thin horizontal layer of a non-magnetic electrolyte containing a bulk solution of salt and carrying an electric current. The layer is bounded by two deformable free surfaces loaded with an insoluble surfactant and is placed in a vertical magnetic field. The arising Lorentz force drives the electrolyte in the plane of the layer. We employ the long-wave approximation to derive general two-dimensional hydrodynamic equations describing symmetric pinching-type deformations of the free surfaces. These equations are used to study the azimuthal flow in an annular film spanning the gap between two coaxial cylindrical electrodes. In weakly deformed films, the base azimuthal flow and its linear stability with respect to azimuthally invariant perturbations are studied analytically. For relatively thick layers and weak magnetic fields, the leading mode with the smallest decay rate is found to correspond to a monotonic azimuthal velocity perturbation. The Marangoni effect leads to further stabilisation of the flow while perturbations of the solute concentration in the bulk of the fluid have no influence on the flow stability. In strongly deformed films in the diffusion-dominated regime, the azimuthal flow becomes linearly unstable with respect to an oscillatory mixed mode characterised by the combination of radial and azimuthal velocity perturbations when the voltage applied between electrodes exceeds the critical value.

Electrocoalescence of W/O emulsions in electric fields generated by matrix electrodes

Waste oil resource treatment can avoid its pollution of the ecological environment, in which the demulsification and dehydration of water-in-oil (W/O) emulsions is crucial for waste oil resource treatment. Electrocoalescence technology has been attracting much attention as a fast-developing emulsion breaking and separation technology with a short development time. In this study, a non-uniform matrix electrode structure is proposed, the effects of a non-uniform matrix electrode on emulsion demulsification and dehydration are investigated experimentally, and the relative benefits of a matrix electrode and a traditional electrode structure are compared and analyzed. According to experimental results, the matrix electrode's dehydration effectiveness at U = 1000 V was 1.59 and 1.29 times greater than that of the parallel plate and coaxial cylindrical electrodes, respectively. The best electric field parameter setting was U = 1100 V, f = 2500 Hz, and δ = 0.5. After electrocoalescence, the water content was 0.60 % and the dehydration efficiency was 94.00 %. This work presents innovative ideas for the design of small and efficient electric coalescers as well as beneficial information for selecting the right electric field parameter. It is conducive to optimizing the resourceful recycling and treatment technology of W/O waste oil.

Динамика водомасляной эмульсии в неоднородном высокочастотном электрическом поле

The article presents the results of an experimental and numerical study of the behavior of a water-oil emulsion in an inhomogeneous electric field conducted to investigate the prospects of using the dielectrophoretic effect for the separation of liquid dispersed media. The problem is considered under conditions of neutral buoyancy of the dispersed phase, when the dynamics of droplet inclu-sions is determined solely by the action of the dielectrophoretic force. The inhomogeneous electric field was created by a system of coaxial cylindrical electrodes. The experiments were carried out in an alternating electric field with a frequency of 10 kHz, which made it possible to avoid the mani-festation of electrophoretic and electrokinetic phenomena. We studied both the dynamics of indi-vidual droplets in an electric field and the change in the content of the dispersed phase at different moments of time. It was found that water droplets always move in the direction of the intensity gradient, eventually accumulating on the internal electrode. The time it takes a single drop to reach the inner electrode significantly depends on its size and the initial distance to the inner electrode, the magnitude of the effective voltage, and the permittivity of the dispersion medium. It is shown that when choosing the initial distance from the drop to the inner electrode and the total time of the drop movement as measurement units for the current distance and time, respectively, the results of all experiments form a single dependence in these dimensionless variables. It was found that the emulsion separation rate increases with an increase in the average droplet size, the effective volt-age, the dielectric constant of the dispersion medium and the initial concentration of droplets. It is shown that in the latter case, the dependence is due to the presence of cases of droplet coalescence, the frequency of which increases with increasing concentration. The results obtained during numer-ical simulation are in good quantitative agreement with the experiment. In conclusion, the results of the laboratory and numerical experiments are compared, the advantages of the proposed method of electrodehydration in comparison with existing approaches are discussed.

Comparing the effects of Cu-Ti/RuO2-IrO2 electrode configuration on the electro-reduction of nitrate.

Nitrate pollution is a global problem as it affects both the environment and human health. The objective of this research was to study the effect of electrode configuration on the electro-reduction of nitrate. Coaxial cylindrical (inner rod and outer tube copper cathodes) and vertical plate parallel copper cathodes paired with Ti/RuO2-IrO2 (rod, tube, and plate) configurations were studied under various current densities and initial nitrate concentrations. The efficiency of each configuration was determined based on the removal efficiency of nitrate, specific energy consumption, mass transfer coefficients, and first order rate constants. Additionally, the overall systems' resistance and geometric factors are discussed. It was found that the performances of the inner rod and outer tube copper cathodes were similar. The vertical plate parallel configuration was superior to the coaxial cylindrical electrode setup, as evident from a higher maximum nitrate removal of 74 and 56% at a current density of 7 mA/cm2 and lower energy consumption of 46.7 × 10-3 and 54.3 × 10-3 kWh/mmol NO3- at 36.4 mA/cm2, respectively. In addition, the mass transfer coefficients and first order rate constants were higher in all conditions tested for the vertical plate parallel configuration.

Development of a microkinetic model for non-oxidative coupling of methane over a Cu catalyst in a non-thermal plasma reactor

A surface microkinetic plasma model for non-oxidative coupling of methane into H2 and higher hydrocarbons was developed over a Cu catalytic film. Twenty key plasma species including electron, ions, radicals, and neutrals were considered in respective chemical reactions leading to the formation of C2 hydrocarbons onto the catalyst surface. The kinetic model was coupled with a global plasma model to describe the performance of a non-thermal plasma reactor. In the reactor model, the reactant gas flows between the two coaxial cylindrical metal electrodes with a length of 50 mm and a diameter of 2 mm (inner) and 6 mm (outer electrode) coated with a Cu film. The effect of discharge power, initial CH4 concentration, and inlet flow rate on methane conversion was investigated. The surface model shows that the CH4 conversion of 47% is obtained at a discharge power of 70 W with a selectivity of C2H2 (49%). Increase in power increased the conversion of methane while increase in pressure and/or inlet gas flow rate decreased it. Also, the results of the plasma-catalyst model were compared with those of plasma alone (without catalyst). It showed that presence of the catalyst inside the plasma increases the selectivity and yield of acetylene, while it deceases the selectivity and yield of hydrogen. Also, the density of radical CH3 in the plasma phase increased in the presence of catalyst, while CH2 and CH densities decreased with that.

Simulation and experimental study on the influence of bit structure on rock-breaking by high-voltage electro-pulse boring

High-voltage electro-pulse boring (EPB) rock-breaking can produce tensile damage, which has significant advantages in deep hard rock drilling. To develop a bit with high drilling efficiency and low energy consumption has become one technical problem in EPB technology. First, based on the electrode structure arrangement and the previous research on EPB mechanism, this paper developed three kinds of electrode bits with a coaxial cylindrical structure, electrode cross structure and multi-electrode pair structure. Second, it established a numerical simulation model of EPB with different-structure bits, and analyzed the influence of different structural arrangements on EPB. Based on the idea of parametric design of electrode bit parts, the influence of the high-voltage electrode shape on EPB was further analyzed. Finally, it built the EPB test units, and carried out the EPB tests of the bits with different structures, and made clear the influence of different structural arrangements on EPB. Compared with EPB experimental results, the bit with a coaxial cylindrical structure had the best drilling effect, followed by the one with a multi-electrode pair structure, and then the one with an electrode cross structure with the same setting of electrical parameters. At the same time, this paper made the EPB experiments on different high-voltage electrode shapes by using a coaxial cylindrical electrode bit. The results showed that the bit with a conical high-voltage electrode had the best drilling effect, followed by the one with a spherical high-voltage electrode, and then the one with a flat bottom high-voltage electrode. Through the simulation analysis and experimental study, this paper concluded the influence law of the bit structure on EPB. The application of the findings was helpful to guide the design of electrode bit structure, reduce energy consumption, and improve drilling efficiency.

Determination of Gas Permeation Properties in Polymer Using Capacitive Electrode Sensors.

The objective of this work was to develop an effective technique for characterizing the permeation properties of various gases, including H2, He, N2, and Ar, that are absorbed in polymers. Simultaneous three-channel real-time techniques for measuring the sorption content and diffusivity of gases emitted from polymers are developed after exposure to high pressure and the subsequent decompression of the corresponding gas. These techniques are based on the volumetric measurement of released gas combined with the capacitance measurement of the water content by both semi-cylindrical and coaxial-cylindrical electrodes. This minimizes the uncertainty due to the varying temperature and pressure of laboratory environments. The gas uptake and diffusivity are determined as a function of the exposed pressure and gas spices in nitrile butadiene rubber (NBR) and ethylene propylene diene monomer (EPDM) polymers. The pressure-dependent gas transport behaviors of four different gases are presented and compared with those obtained by different techniques. A linear correlation between the logarithmic diffusivity and kinetic diameter of molecules in the gas is found between the two polymers.

Measurement Uncertainty in Voltage Coefficients for Compressed-Gas Capacitor Based on a Simplified Tilting Method

High-voltage compressed-gas capacitor is a type of precision equipment commonly used in high voltage laboratories. The voltage dependence of capacitance, in other words, the voltage coefficient of capacitance, is an important factor to ensure the measurement accuracy of capacitors. The simplified tilting method derived from PTB, which provides a solution for measuring the voltage coefficient of the high-voltage capacitor with compressed-gas coaxial cylindrical electrodes structure. However, it is not an easy work for most laboratories. In order to evaluate the voltage coefficient based on the simplified tilting method, a special experimental platform was developed. The high-voltage capacitor installed on the platform can be tilted and rotated at high voltage and be remote-controlled. Base on the developed platform, the voltage coefficient of a 350 kV high-voltage capacitor was measured. In order to verify, it was re-measured by the direct measurement method with a dummy high-voltage capacitor, and before that, the voltage coefficient of the dummy capacitor was calibrated with a near zero-voltage-coefficient capacitor. The results show a good agreement, the consistency of the measurement results is better than 1.2×10^-6 between the two methods. Furthermore, the evaluation of measurement uncertainty in the voltage coefficient determination of capacitor based on simplified tilting method is introduced in detail. The evaluation results show that the expanded uncertainty is significantly better than 2.0×10^-6, k=2.

Finite-Element Simulation of Effect of Surface Roughness of Coaxial Cylindrical Electrodes on Small Mass and Force Measurements Using Voltage Balance Apparatus

A voltage balance apparatus that uses the electrostatic force between coaxial electrodes was developed at the National Metrology Institute of Japan for the accurate and traceable measurement of small masses and forces with respect to the new definition of the kilogram. To achieve accurate measurements using the voltage balance, the coaxial electrodes of the apparatus were mechanically aligned by measuring their capacitances. In this study, we investigated the effect of the surface roughness of coaxial electrodes on the capacitance gradient and mass measurements in voltage balance measurements using the finite-element method for 2-D electrostatic problems. The results suggest that when the surface roughness of the electrodes was less than a few tens of micrometers in the average value of the absolute values of roughness height, they did not significantly increase the errors in the capacitance measurements due to mechanical deformation.

Accurate and Efficient Calculation Method for Ion Flow Field Near Direct Current Voltage Divider

The surface of grading rings in DC voltage divider may cause surface wear or scratch, resulting in corona phenomenon. Due to the influence of space charges and surface charges, the total electric field near DC voltage divider is different from the nominal electric field. For the problem of solving the ion-flow field near the DC voltage divider, this paper proposes an improved method based on upwind Finite Element Method (FEM). According to the nominal electric field results, the updated switch state of the charge density is determined, and then the upwind FEM is used to update the node charge density. This method uses a dual-scene iterative method to converge for the multiple grading rings, which improves the convergence. The correctness of the method is verified by the coaxial cylindrical electrode. Finally, the ion-flow field near 500 kV DC voltage divider is calculated. The results show that the total electric field near the grading ring becomes more uniform due to the effect of space charges and surface charges. In the space far from or close to the grading rings, the total electric field will increase or decrease compared with the nominal electric field. The method in this paper provides guidance for the calculation of the ion-flow field near the DC divider and its insulation design.

Weight analysis and experimental study on influencing factors of high-voltage electro-pulse boring

Electro-pulse boring (EPB) has the advantages of high rock-breaking efficiency and good borehole wall quality, which is a new type of rock-breaking method with potential and close to industrialization. EPB is affected by many factors, such as voltage, electrode structure shape, rock composition, discharge times and so on. Firstly, according to the established simulation model of EPB and the previous research on electric breakdown model of rock, the maximum electric field strength in rock, the electric breakdown field strength of rock and its ratio with different influencing factors were simulated and calculated. Secondly, the probability of electric breakdown with different influencing factors was obtained. The extreme learning machine and average influence value (ELM-MIV) algorithm was proposed to analyze the weight of the six influencing factors on the probability of electric breakdown, such as peak voltage, electrode spacing, electrode angle, and so on. The correlation and contribution degree of the influencing factors on the electric breakdown probability were obtained. Then, the EPB experiment system based on the transformer-type pulse power supply was developed, and the coaxial cylindrical electrode bits with the spacing of 25 mm and 45 mm were developed. The drilling diameter of red sandstone was 100 mm and 60 mm, respectively. The results showed that the energy consumption of EPB was about 100–300 J/cm3 without slag discharge system. Finally, the influence experiments on EPB were carried out, and the influence rules of electrode spacing, discharge times and rock composition on EPB were obtained. It provided guidance and basis for the design of electrode bit and the selection of drilling technology parameters in different strata through the research on the influencing laws of EPB. It was of great significance to improve the efficiency and reduce the energy loss in the process of EPB.

Optimization of discharge circuit model based on electro pulse boring experiment

High-voltage electro pulse rock-breaking is a green breaking technology, which can achieve high efficiency of rock-breaking. It has a wide application prospect in deep and ultra-deep well drilling and tunnel driving in the future. Pursuant to the time delay characteristics of the gas discharge switch in the electro pulse boring (EPB) system, the equivalent model of the discharge circuit is established based on the time-varying resistance model. With this model, the real-time parameters such as voltage, current and discharge energy can be predicted in the EPB process of different rocks. In line with the arrangement of coaxial cylindrical electrodes, a 25 mm electrode drill bit is designed, and an EPB experiment system is developed based on the transformer step-up pulse power supply. The electro pulse breaking of red sandstone, yellow sandstone, concrete and granite, and the complete drilling of 60 mm diameter in red sandstone and concrete are realized, and EPB rules of different rocks are obtained. The real-time curves of electrical parameters in different rocks are collected by electrical parameter tester. The model parameters are identified based on the least square method of unconstrained nonlinear optimization. The current curve fitted by the identification parameters and the current curve obtained from the experiment are featured in high coincidence and good follow-up, which proves the accuracy of the optimized model and parameter identification. The optimization of the discharge circuit model and the identification of the model parameters based on EPB experiment are of great significance to guide the selection of the technological parameters of EPB, improve the efficiency of rock-breaking and reduce the energy loss in the drilling process.

Experimental and numerical analysis of a new tribo-electrostatic separator with coaxial cylindrical electrodes for plastic binary granular mixtures

This paper is aimed to the description of a new tribo-electrostatic separation process where the top part of the separator is constituted by two coaxial electrodes and the bottom part comprises two cone-shaped electrodes. An experimental and a numerical analysis were carried out in which the main significant factors were investigated. The experiments carried out on three different binary mixtures of mm-size PA (polyamide), PC (polycarbonate) and PVC (polyvinyl chloride) particles showed that more than 80% of the total mass is recovered with high purity values up to 90%.

Two-dimensional analytical investigation into energy conversion and efficiency maximization of magnetohydrodynamic swirling flow actuators

The azimuthal Lorentz-force-driven magnetohydrodynamic swirling flow between coaxial cylindrical electrodes with an imposed axial magnetic field has extensive application in the swirling actuators. To identify the mechanism of energy conversion within the flow-discharge nonlinearly coupled field, we develop a 2-D analytical functional model bridging the gap between the imposed magnetic field distribution and the magnetohydrodynamic fields. With Hall effect present, the analytical solution is found to be controlled by the Reynolds number and a newly defined dimensionless number (K) deduced from the Hartmann number and the Hall parameter. The solution is confirmed with numerical and experimental results. By virtue of its analytic nature, the model provides more convenient insight and understanding into energy coupling and efficiency optimization. Based on this model, the nonlinear coupling relationship between the total voltage and the electromotive force is identified. The most striking contribution is the identification of double barriers, induced by Hall effect and viscosity, to maximize system efficiency through the model. To achieve efficiency maximization, the optimum magnetic field distribution is found by solution of the functional extremum problem derived from the analytical model.

Impact of Pulsed Electric Field on Glycerin Sedimentation from Biodiesel Production Process

This research aims to study the impact of continuous pulsed electric field (PEF) on glycerin separation from Transesterification process. Transesterification process of biodiesel production using 100 ml vegetable oils with alcohol of 1:5 molar ratio together with potassium hydroxide (KOH) as catalyst 1 wt.% for the reaction. The designed glass tube reaction chamber is 250 ml contained with coaxial cylindrical electrodes. The applied voltage to an electrode was at 1 kV and frequency of 1 kHz with pulse duration of 500 μs and also 4 kHz with pulse duration of 125 μs. The results showed that the glycerin volume from transesterification process has rapidly sedimented with pulsed electric field method. It is much faster than using conventional gravity method. The sedimentation rate increases rapidly with an increasing in frequency of the applied voltage. The highest volume of glycerin sedimentation of 10.2 ml is by using pulsed electric field at 1 kV and 4 kHz.

Glycerin Separation from Biodiesel Transesterification Process by Pulsed Electric Field with Specific Pulse Forming Network

Biodiesel production process can be rapidly done if the glycerin separation can be removed faster. With the palm oil crisis, biodiesel is needed for faster production to add more value and to solve the oversupply problem. Pulse forming network circuit can generate pulsed electric field (PEF) to speedily separate glycerin from biodiesel production. While the substance is reacting, the electrical impedance value of glycerin is changed, the pulse forming network will keep waveform to be a square wave. Transesterification process using palm oil mixed with methanol with a molar ratio of 1:6 by using 1 wt.% of KOH as a catalyst. The reaction chamber electrode was coaxial cylindrical electrodes with diameter 6 cm and 1 cm. The maximum voltage across the reaction chamber is 500 V with 1, 5 and 10 kHz frequency. Glycerin separation was best achieved when using 5 kHz frequency. The glycerin was obtained at 155 ml in 20 minutes.

Interfacial reinforcement of hybrid composite by electrophoretic deposition for vertically aligned carbon nanotubes on carbon fiber

In this paper, vertically aligned carbon nanotube/carbon fiber (VACNT/CF) hybrids was prepared by electrophoretic deposition (EPD) under mild conditions. The coaxial cylindrical electrode with CF filament as the cathode was employed to ensure dense VACNT arrays deposited on CF surface at low deposition voltage. The effect factors on the carbon nanoparticles alignment were investigated by the micro-morphology observations of hybrid fibers, including the diameter of carbon nanoparticles, types of solvent, deposition voltages, deposition time and the concentrations of carbon nanoparticles in dispersion. The results indicate that the optimum electrophoretic deposition conditions for vertically aligned hybrid fibers is the diameter of carbon nanoscale reinforcements of 110–170 mm, acetonitrile (ACN) as the dispersion medium, deposition voltage of 30 V, deposition time of 20 s and dispersion concentration of the carbon nanoparticles of 0.01 mg/mL. Single fiber tensile testing was performed and manifested that EPD in a coaxially cylindrical electric field was not destructive and could preserve the mechanical properties of CF filaments. Results of interphase properties tests demonstrated that the contact angle and the interfacial shear strength (IFSS) were significantly improved by 48.3% and 58.1% compared to that of as-recieved CF, respectively. The interfacial enhancement mechanism was also explored in details.

Electric field measurements under DC corona discharges in ambient air by electric field induced second harmonic generation

Electric field distribution is critically important for quantitative insights into the physics of nonequilibrium plasma like corona. To analyze the electric field as well as the ion flow (space charge) distribution under DC corona discharges, the ion flow model has been widely adopted; Kaptzov's assumption, which states that the steady state electric field at the conductor surface remains at the corona onset value, serves as a boundary condition. In this Letter, we investigate the electric field distribution under DC corona discharges between coaxial cylindrical electrodes in ambient air by electric field induced second harmonic generation with nanosecond pulse laser beams. The electric field distribution (with or without the corona discharge) is obtained. By comparing the measurements with the results predicted by the ion flow model for the negative corona discharge, it is found that the electric field at the conductor surface is proportional to the current density of the corona discharge with a negative constant of proportionality. Therefore, for negative corona discharges, Kaptzov's assumption is valid only when the discharge current approaches zero or is small.

Curvature affects electrolyte relaxation: Studies of spherical and cylindrical electrodes.

With two minimal models, I study how electrode curvature affects the response of electrolytes to applied electrostatic potentials. For flat electrodes, Bazant etal. [Phys. Rev. E 70, 021506 (2004)PLEEE81539-375510.1103/PhysRevE.70.021506] popularized the RC timescale λ_{D}L/D, with λ_{D} being the Debye length, 2L the electrode separation, and D the ionic diffusivity. For thin electric double layers near concentric spherical and coaxial cylindrical electrodes, I show here that equivalent circuit models again predict the correct ionic relaxation timescales. Importantly, these timescales explicitly depend on both electrode radii, not simply on their difference.

Effect of Temperature on the Working Parameters of Negative Corona Discharge with Coaxial Electrodes Configuration

The influence of ambient temperature on the various parameters of negative corona discharge in atmospheric dry air with coaxial cylindrical electrodes is investigated. The calculations are achieved using the finite element method by COMSOL Multiphysics software. The investigation aims to notice the effect many of working temperatures on the I-V characteristic curve of negative corona discharge in the air. The calculations of several parameters (electron density, temperature, ...) are presented visually and discussed. The results of the work are compared with theoretical and experimental data and they are in a good agreement.