Variation Of Electric Field Intensity Research Articles

The effect of nozzle spacing on the electric field and fiber size distribution in a multi‐nozzle electrospinning system

AbstractThe present study investigates the characteristics of nanofiber uniformity in a multi‐nozzle electrospinning system widely used to prepare nanofiber matrix. The effect of nozzle spacing on the electric field and nanofiber diameter uniformity is analyzed using a four‐nozzle electrospinning system. The electric field distribution at the nozzle tip at different nozzle spacings is simulated numerically using COMSOL Multiphysics 5.6. Simulation results find that as nozzle spacings increase from 1 to 5 cm, the average electric field intensity at 1 mm from the tip of four nozzles increases from 32.46 to 40.08 kV/cm. Variations of electric field intensity at a given spacing decrease from 11% to 3.2% for spacings of 1 to 5 cm. Corresponding experiments are conducted with a gelatin solution. As the nozzle spacing increases, the four nozzles produce nanofibers with diameters of 88–508 nm, 112–498 nm, and 90–418 nm. Nanofiber diameter uniformity increases, and the average diameter decreases from 268 to 222 nm. In addition, the effect that changes in voltages and nozzle‐to‐collector distances have on fiber diameter is also studied. The experiments show that nanofiber diameter decreased as voltage increased and increased as nozzle‐to‐collector distance increased.

Dielectric relaxation behaviors and dissipation characteristics of colloidal nanocarbon (graphene and CNTs) complex fluids

The present article reports the dynamic complex dielectric responses of non-polar nanocolloids of graphene (G) and carbon nanotubes (CNTs). The frequency dependent complex relaxation behaviors of G and CNT colloids were determined in the range of 100 Hz to 3 × 105 Hz employing dielectric spectroscopy at a constant temperature. The governing roles of nanostructure concentration, conductivity, frequency, and amplitude variation of the forcing electric field on the dielectric response have been examined. The experimental observations reveal that the presence of G or CNT, as well as their concentrations, significantly governs the overall dielectric responses of the nanocolloids. The dilute and concentrated colloids display grossly distinguishable capacitive and dissipative behaviors, hinting at the major role of concentration regimes on the dielectric behavior of such colloids. In addition, the variation of electric field intensity results in altering the dielectric responses of the colloids, which points at the role of polarization of the nanomaterials on the overall dielectric relaxation. To model the complex dipolar interactions, the classical Havriliak-Negami model is employed and good agreement has been achieved against the experimental observations. It has been observed that increasing nanomaterial concentration and field amplitude has a dominant influence upon the relaxation parameters. Further, the effects of colloidal concentration on the AC and DC conductivity modes have also been analyzed. The conductivity response of the colloids has been explained by appealing to percolation theories. The present article may find strong implications toward the design and development of liquid dielectric based electrical and electronics systems.

Analysis of the unique case of ball lightning observation in Mitino, the northwest district of Moscow

Observations of eyewitnesses are the main source of data on ball lightning (BL) properties, but often their descriptions turn out to be incomplete, contradictory and lacking in details. Recently due to the wide use of digital camcorders, still cameras and smart-phones the appearance of a large number of video films enable to study the properties of these objects in more detail. However, even the film caught by the lone observer doesn't allow measuring such the important properties as the dimension of the object and the distance to it. On 27 July 2015 the unique event occurred: BL was simultaneously recorded by three observers located at different points. This allowed us to determine a distance to BL, its diameter (0.75 m) and velocity of its motion at various moments of time. BL movement could be broken into three stages. At first it was approaching to the observers with a velocity of the wind. Then for about 80 s it was moving at a height 40–50 m inside a restricted region with a width 12 m and a length 100 m. At the last stage it rose with a velocity 5.7 m/s to the approaching cloud and flew away with a velocity of the wind 15 m/s. The analysis has shown that such a character of BL motion can be explained if to assume that BL has a positive electric charge (Qbl = 10−3 C) and its attraction to the storm cloud (Qc = 5 C) compensates the wind pressure on BL. Stabilization of BL position at a height 40 m can be explained by variations of electric field intensity above the treetops, by instabilities of wind direction or by BL rotation around a horizontal axis with a linear velocity 0.84 m/s. Evaluations showed that the nearby electricity line did not affect BL motion. The details of BL behavior may serve as an evidence for its material nature.

Electrochemical machining of blades with cross-structural cathodes at leading/trailing edges

Blades are key components in modern aero engines. Their leading and trailing edges are extremely difficult to machine using electrochemical machining (ECM) because of their small thickness and radius of curvature and their marginal location. Traditional ECM of blades requires gaps between the convex part cathode and concave part cathode at the leading and trailing edges to allow passage of electrolyte. The presence of these gaps may lead to large variations in electric field intensity at the end of the machining process as the leading and trailing edges are forming. This paper proposes a new design of cross-structural cathodes to decrease the dynamic variation of the electric field at marginal locations. A mathematical model of material removal is established, taking account principally of the electric field factor. The forming process of the leading edge is simulated, and changes in electric field intensity during the final stages of the process are analyzed. The simulation results show that the maximum fluctuation in the electric field intensity at the leading edge is 62.42% when a conventional cathode is used, but only 30.51% with cross-structural cathodes. Experiments are conducted to compare the performance of conventional and cross-structural cathodes. The results show that, in comparison with conventional cathodes, the use of cross-structural cathodes reduces variations in machining current in the forming stage of margin profiles and leads to more accurate repeatability of the process.

Design of a Concentration Sensor Based on Photonic Crystal Fiber Placed between Two Single Mode Fibers

We demonstrate the use of photonic crystal fiber (PCF) joined in between two single mode fibers (SMF) as a concentration sensor. To realize this, one micrometer length PCF of hexagonal lattice is sandwiched between two SMF having one micrometer length each. To maximize the coupling between SMF and PCF, the core diameters are made equal. Then the output from a given input through this structure is analyzed with respect to different concentrations in the air holes of PCF using Finite Difference Time Domain (FDTD) method. It is found that the variation of electric field intensity at the output is linear with respect to concentration of alcohol.

Estimation of Soil Electrical Properties in a Multilayer Earth Model with Boundary Element Formulation

This paper presents an efficient model for estimation of soil electric resistivity with depth and layer thickness in a multilayer earth structure. This model is the improvement of conventional two‐layer earth model including Wenner resistivity formulations with boundary conditions. Two‐layer soil model shows the limitations in specific soil characterizations of different layers with the interrelationships between soil apparent electrical resistivity (ρ) and several soil physical or chemical properties. In the multilayer soil model, the soil resistivity and electric potential at any points in multilayer anisotropic soil medium are expressed according to the variation of electric field intensity for geotechnical investigations. For most soils with varying layers, multilayer soil resistivity profile is therefore more suitable to get soil type, bulk density of compacted soil and to detect anomalous materials in soil. A boundary element formulation is implemented to show the multilayer soil model with boundary conditions in soil resistivity estimations. Numerical results of soil resistivity ratio and potential differences for different layers are presented to illustrate the application, accuracy, and efficiency of the proposed model. The nobility of the research is obtaining multilayer soil characterizations through soil electric properties in near surface soil profile.

Effects of rubbing angle on maximum transmittance of in‐plane switching liquid crystal display

Measurements of the maximum transmittance of an in‐plane switching liquid crystal display showed that it increases as rubbing angle is increased from 10 to 20°. This dependence was analysed in terms of the local variation of electric field intensity between electrodes, which in turn makes liquid crystal at various positions between the electrodes rotate to different angles. The local variation of electric field becomes prominent, especially in the case that the distance between the electrodes is much larger than the cell gap or electrode width.

Impulse flashover along the outer surface of a cylindrical dielectric solid with a gas layer inside

Impulse flashover voltage along the outer surface of a layered dielectric composition, composed of two coaxial hard glass cylinders and an inner gas layer, is known to have a V-shaped curve as a function of pressures inside the gas layer. It is the purpose of the paper to clarify the reason for this V-shaped curve. Variation of electric field intensity along the outer surface caused mainly by ionisation in the gas layer, and partly by the residual charges on the inner surface of the outer cylinder is found to play an important role in determining the flashover voltage

Dynamics of electrical parameters of an arc and its behavior in a plasmatron channel

Stability of burning of the arc in a plasmatron channel depends on the dynamic as well as the static characteristics of the arc. Many investigations show that the dc arc in a plasmatron is not a stationary phenomenon; the current, the voltage, and also the length of the arc in the channel are all subject to oscillations. Steady pulsations of the electrical parameters are due primarily to the arc shunting process. Nonstationary processes also exist that are not connected with shunting. To speak in terms of a region of the U-I characteristics it can be said that greatest interest centers on the dynamical processes on the rising part of the characteristic. It has previously been shown [1] that the rising branch of the E-I relation has local regions where the electric field intensity of the arc falls with increasing current, such singularities failing to be reflected by the overall static U-I characteristic. This process whereby the overall volt-ampere characteristic is “smoothed out” is connected with certain variations in the structure of the arc in the channel and with the appearance of electrical oscillations. The present paper presents the results of an experimental study of the electrical parameters of the arc in a plasmatron channel and its behavior for a rising volt-ampere characteristic. The rising part is found to exhibit unstable regions, where the arc current and voltage “oscillate.” The structure of the arc in the channel changes sharply under unstable conditions. The reason for the appearance of instability is the singularity in the variation of electric field intensity with current on the rising portion of the characteristic.

Transport Phenomena in Partially Ionized Cesium

An analysis of electron and ion transport phenomena in cesium plasma is developed in a form consistent with experimental conditions typical of those in thermionic and magnetohydrodynamic energy converters and other cesium discharges. Particular attention is given to electron collision processes which are shown to influence significantly both electron and ion transport phenomena. Using available electron cross-section data, electron and ion transport coefficients are evaluated as a function of electron temperature and fractional ionization. Results are then applied to the plasma of a low-pressure nonuniform thermionic arc. Experimentally determined spatial variations of electron density and electron temperature are analyzed numerically and quantitative estimates are made of the spatial variation of electric field intensity, ion current density, and net charged particle production rate. The inferred production rate is compared with that evaluated using a nonequilibrium kinetic analysis developed by Norcross and Stone.

Electron-Transport Phenomena in Thermionic Converter Plasmas

An analysis of electron transport phenomena is developed in a form consistent with conditions known to exist in thermionic converter plasmas. Particular attention is given to the contribution of electron-ion collisions to the electron momentum transfer collision frequency, and the resultant dependence of the plasma transport coefficients on ion density which itself depends upon interelectrode position. Experimentally determined spatial variations of electron density and electron temperature are analyzed numerically for a variety of converter operating conditions and quantitative estimates are made of: the spatial variation of electric field intensity and electrostatic potential in the plasma, the spatial variation of electron kinetic energy flux, and the relative importance of electron energy gain and loss processes in the interelectrode region. On the basis of these results, an interpretation is made of the role played by the cesium neutralization plasma in determining converter performance.