Journal of Electrostatics最新文献

The DEVCOM Army Research Laboratory (ARL) electric field “cage” generates a uniform E-field over a large working volume, along the lines of the IEEE-Std 1308–1994. The end plates are spaced farther apart than the IEEE standard field source, and the fringing fields are controlled by the addition of “guard tubes.” This chamber was originally constructed to calibrate and characterize electric field sensors, and it has been redesigned to support quasi-static electric field imaging applications. A planar array of sensors forms a grounded end plate of the cage and is used to measure distortions in the uniform field generated by the cage due to objects placed inside. However, the array itself distorts this field and introduces significant errors. Several modifications were made to mitigate the errors, including adding nonfunctional “dummy” elements, a border around the array, and a back plane behind it. The parameter space for these additions is very large, since the number of nonfunctional elements, the width of the border, and the size and placement of the back plane can all be tuned independently. Extensive computer modeling was used to explore this parameter space and test thousands of possible designs. The design chosen yields modeled absolute field errors over a 1.2-m × 0.8-m sensing plane that are less than 0.5 % for a uniform ambient field (empty cage), and less than 1 % for a sphere with a 0.5-m radius in an ambient field.

Safe practice requires that the use of insulators is avoided in hazardous areas containing potentially explosive atmospheres. However, in some processes, insulators are essential components and cannot be replaced by conducting materials. Evaluation of insulators for safe use in hazardous areas is discussed with particular reference to the requirements of international standards. Examples of testing by the measurement of transferred charge in brush discharges from insulating materials are presented, which indicate that using different size electrodes than specified in international standards can result in higher or lower measured transferred charge, and can, in some cases, lead to a different test outcome and evaluation of safety. The examples presented are from commercial testing and are included in this short communication to illustrate issues that the author has experienced when implementing international standards.

The elimination of electrostatic charges, especially on material webs is critical to preventing ignition hazards and personal injury hazards in industry. The use of discharge bars (called “ionizers”) is an important method for eliminating electrostatic charges.

The possibility of electrostatic discharge in a production machine is real. The metrological detection of charges on material webs is also discussed and the special phenomenon of a super brush discharge is described. A useful arrangement for active ionizers is described and justified.

Previous studies have shown that electrohydrodynamic (EHD) gas pumps are a viable alternative for traditional fans. In this study, it further demonstrates that an EHD gas pump is a device particularly ideal for cooling electronic components. To this end, four electronic components which are individually mounted on each wall of a horizontal channel are cooled by a two-stage EHD gas pump. To evaluate the effectiveness of EHD gas pump, two electrode configurations are considered; aligned and offset. Three heat dissipation rates are considered: 100 W/m², 200 W/m² and 500 W/m². The average surface temperature and the maximum temperature (i.e., the hot spot) of each electronic component are carefully examined. The results are compared with those obtained without using an EHD pump. It shows that an EHD pump with offset electrode configuration produces the best cooling effect as it generates more mixing of flow inside the channel. The average surface temperature and the maximum temperature on the electronic components cooled by EHD gas pump with offset configuration are lower than those cooled by EHD pump with aligned electrodes. More importantly, the results show that the performance of EHD pumps in terms of energy efficiency may be further improved when the two stages are operated in uneven voltages.

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.