Journal of Electrostatics最新文献

Understanding and modelling the static charge decay on an insulating material surface have been the topic of numerous research works since the nineteenth century. After an introduction on this historical context, a selection is presented here covering the various phenomena that may be held responsible for the decay: ion deposit from the surrounding atmosphere, charge injection and transport through the conduction and trapping levels of the solid, internal polarization by free carrier motion or dipole polarization, as well as surface conduction and migration of the deposited charge along the surface.

Surface potential measurements are a convenient technique to study these various types of charge motion but the underlying complexity concerning their interpretation is often neglected. Depending on the context, the law of electrostatics may produce a hyperbolic as well as an exponential decay. On an insulating polymer, or any other disordered insulator, charge transport is dispersive, and conduction as well as dipolar polarization responses are described by time power laws. The knowledge of this time response is not sufficient to build a convincing physical model, because of the universality of this response, which leaves many degrees of freedom to interpret the data. Knowledge of the possible elementary processes and their signatures in the observables is therefore requested before the implementation of curve-fitting procedures.

In this paper, the elemental composition and morphology of fly ash particles after wood pellets combustion in low-power domestic boiler and removed by electrostatic precipitator were investigated by EDS, XRD and SEM methods. The gaseous products discharged into the atmosphere were identified by the FTIR method. Because fly ash particles are usually exhausted to the atmosphere, new constructions of small electrostatics precipitators for domestic use were proposed in recent years in the literature, for the collection of fly ash particles emitted by such boilers fired by biomass fuel (wood pellets) or by coal. The goal of this study was to characterize the combustion products retained at various places from boiler to stack, i.e., beneath the grating (as bottom ash), on heat exchanger, inner walls of stack, and the collection electrodes of electrostatic precipitator. It was shown that the precipitated biomass fly ash comprises of large irregular particles, which were the agglomerates of primary nanoparticles or unburned fragments of fuel (biomass pieces). These particles were composed mainly of K, Cl, Ca, C, O, P and S (>1 at.%).

The deployment of dc electric field sensors in outdoor environments requires a fully sealed enclosure to shield them from environmental damage. This paper explores the behavior of an electric field sensor housed within a grounded enclosure featuring an electrically floating cover plate. A capacitance model was developed for this configuration, revealing that a conducting extension pin positioned between the cover plate to a position closely above the sensor can enhance the field strength experienced by the sensor. In the experiment, when the aperture of the enclosure measures 30 mm × 30 mm, the floating plate dimensions are 15 mm × 15 mm, and the pin diameter is 4.6 mm, with the pin positioned 1 mm above the sensor, the detected field strength is amplified by a factor of 8.9 compared to when the extension pin is absent.

We present multipole expansion of electrostatic potential in cylindrical coordinates which contains triple summation in terms of associated Legendre polynomials. Multipole moments of presented expansion depend only on charge distribution and can be easily calculated analytically for cylindrically symmetric and other charge distributions with simple representation in cylindrical coordinates. Presented multipole expansion is employed in order to calculate potential of uniformly charged solid cylinder. Correctness of derived multipole expansion is verified by comparing multipole expansion of potential produced by uniformly charged solid cylinder with known expression for potential on its axis.

A comprehensive approach to lightning protection is comprised of four key steps, namely protection against direct lightning strikes, dealing with surges and transients, dissipation of lightning currents via earthing and bonding, and protecting people. This paper deals with new research findings associated with direct-strike protection with lightning rods or “air terminals”, namely the effect of accumulated corona space charge around the tips of these components. There is now a great deal of consensus amongst lightning researchers and practitioners that space charge accumulation reduces the efficiency of an air terminal by inhibiting the initiation and development of an upward leader, a critical stage in the lightning attachment process. The paper describes measurements carried out in a high-voltage laboratory to quantify the amount of corona discharge that would be emitted under thunderstorm conditions from a variety of air terminals of different geometries. A unique, previously unreported aspect of these experiments was the corona testing of air terminals under dry and wet conditions. The results of these experiments showed that corona discharge (and hence space charge accumulation) from a standard Franklin rod is substantially higher than from the range of significantly blunter “corona minimising” air terminals that were tested. The previously reported polarity difference in corona characteristics was also observed, i.e., the magnitude of negative corona was larger than positive corona for the same ambient electric field. Differences in corona discharge were also observed under wet and dry conditions, where wet air terminals were found to produce modestly more corona. The paper then addresses the optimisation of air terminals, i.e., minimising corona discharge, for practical lightning protection applications, where the air terminal radius of curvature is tailored to its height and position of installation. Various researchers have made these calculations, the outcomes of which are summarised in this paper. In general, radii of curvature in the range 1–100 mm are required, depending on the installation height and location of the air terminal.

The droplet dynamic model under an electric field is established in this paper by coupling electric equations, multiphase flow equations, and isoAdvector interface capture method, accurately predicting the deformation and rupture characteristics of multiple emulsion droplets affected by an electric field. The evolutions of the flow field and electric field during the deformation and breakup processes of multiple emulsion droplets subjected to an electric field are elucidated and the effects of the electric capillary number Ca and the radius ratio R^∗ of the inner and outer droplets on the characteristics of droplet deformation and rupture are analyzed. The results show that in the silicone oil/water emulsion system, the inner droplet is difficult to induce charge since the electrostatic shielding effect of the outer droplet, and it has no impact on the equilibrium deformation of the outer droplet; whereas in the castor oil/silicone oil emulsion system, the charge is induced on the interfaces of both the internal and external droplets and the internal droplet has a remarkable impact on the equilibrium deformation of the external droplet. Furthermore, deformation-breakup phase diagrams of multiple emulsion droplets exposed to the electric field are obtained. As R^∗ increases, the Ca_c for droplet breakup decreases, indicating that the internal droplet intensifies the breakup of the external droplet. The results are significant for the promotion and application of electric field-driven droplet manipulation technology.

Lightning fire is one of the biggest dangers for chemical and petrochemical storage tank farms, particularly in floating roof oil tanks (FROTs). To improve the lightning protection of FROTs, the process of floating roof tanks affected by lightning is analyzed. Lightning inductive effects can result in the undesired operation of the above-ground storage tank equipment and endanger exploitation safety. The time domain finite element analysis based on the transmission line model (TLM) method is regarded as a numerical technique to solve field problems by implementing circuit equivalents. This study aims to analyze lightning strike characteristics using the Heidler current function and simulate electromagnetic field strength (EMFS) distribution and surface current density (SCD). Calculation of minimum possible effective strike distance and shielding effectiveness (SE) is performed. Parametric modeling ensures accurate modeling of the roof's bypass conductor to the shell. By utilizing the Parameter Sweep technique, multiple simulations can be carried out with varying structure parameter values. This approach ensures optimal efficiency and accuracy in the results obtained.

Electrohydrodynamic (EHD) printing has been recognized as a promising additive manufacturing technology with superior pattern resolution and economic viability. The shape of Taylor cone is deemed a pivotal element for the amplification of deposition efficiency, and the maintenance of consistent operational steadiness in EHD printing. The correlations between diverse operating parameters and the shape of Taylor cone are presently not well investigated. In this paper, modeling of relationships between operating parameters and the shape of Taylor cone was conducted with a backpropagation neural network (BPNN) and a genetic algorithm optimized backpropagation (GA-BP) neural network. Taylor cone semi-vertical angle and the meniscus height were employed as two indexes to characterize the shape of Taylor cone. The prediction accuracies of BPNN model and GA-BP model were 92.79 % and 95.46 %, respectively. The GA-BP model demonstrated higher precision in forecasting the shape of Taylor cone. A predictive framework for the shape of Taylor cone was proposed, which provided a practical tool for process optimization in EHD printing.

Molecular dynamics simulations are used to study the mechanisms of droplet electrocoalescence and their importance in understanding the microscopic motion of matter and validating existing theories. This review summarizes recent advancements in the use of molecular dynamics simulations to study droplet electrocoalescence and its influencing factors. The limitations of current research and future directions for further development are discussed. The importance of studying the interactions between different components under the influence of electric fields is highlighted. Suggestions for future investigations are proposed based on the current research status.

In printing applications, microparticles are commonly triboelectrically charged with larger carrier particles. Here, we develop an impaction-differential mobility analyzer-optical particle spectrometer (DMA-OPS) system to examine the size-dependent charge distributions of toner particles in the 0.3 – 10 $\mu m$ range resulting from triboelectric charging via acrylic-coated ferrite carrier. The toner-carrier blend is aerosolized, and toner particles are released from the carrier via inertial impaction of toner-carrier complexes. The toner particles are then classified by electrical mobility and their optical diameters are determined. We can produce toner particle size-dependent charge distributions, which can be converted to surface potentials, and charge-to-mass ratios.