Journal of Electrostatics最新文献

Gas ionizator is a device for electrostatic precipitation and is widely used to separate fine particulate matter (FPM) from small- and large-scale industrial exhaust gases. Two variations of electrodes design, rod and rectangle-toothed saw were used. The mass and number concentrations of six FPM fractions were detected. Stronger vortices occur at higher EAD/Re² ratios compared to the secondary electroaerodynamic (EAD) gas velocities. A deposition efficiency higher than 94.9 % was achieved at a gas velocity of 0.2 m/s. The FPM capture efficiency at voltage up to 20 kV is higher more than 7 % than at a voltage of 15 kV.

In the past few decades, atmospheric plasma propulsion has sustained a growth of interest. Recent studies have demonstrated the feasibility of light air-breathing plasma-propelled aircraft near ground level. Typically, corona discharge actuators are employed. Yet, the effects of the freestream velocity on the discharge current, ionic wind, and thrust must be characterized. The present study focuses on a wire-to-cylinder and a wire-to-airfoil actuators in a wind tunnel in a co-flow configuration. Discharge current and PIV (particle image velocimetry) measurements were used to determine both the differences between the two collecting electrodes and the aforementioned effects of the freestream velocity. The measured current follows the modeling already reported in the literature with a linear increase of the current with the freestream velocity. Besides, an interaction occurs with the charge density between the electrodes, which strengthens the rise of the current with the velocity as the voltage increases. In the study, the charge density increases linearly with the voltage with a slope of 0.75 mC/m²/kV for both collectors. However, the airfoil collector results in a higher current than the cylinder at the same voltage. The local velocity increases in three main regions thanks to the ionic wind. With both actuators, a higher velocity was captured with actuation on the upper and lower surfaces of the collectors. With the cylinder, the interelectrode region experiences a notable rise in velocity as well. In all cases, the air velocity downstream of the actuators is increased by the actuation. The ionic wind is usually less than 1 m/s (around 0.3–0.5 m/s on average) and its effect on the incoming flow decreases when the velocity increases up to 10 m/s. The force was calculated in control volumes around the actuators. For both actuators, the electroaerodynamic (EAD) force is governed by the current, and at constant current, the same EAD force is obtained with the two collectors. Yet, the force decreases with the drag of the collector, leading to a cancellation of the thrust when the drag exceeds the EAD force. At the maximum current tested in the study, the cylinder collector cancels the thrust at around 3 m/s of freestream against 5 m/s with the airfoil, showing that this type of propulsion is currently only applicable to low-speed aircraft.

Presented study investigated the impact of a stationary electric field with an average value of 185 kV/m on the germination process and early growth of radish (Raphanus sativus – a eudicot plant) and oat (Avena sativa – a monocot plant). Electric field stimulation may prove to be one method to sustainably increase crop efficiency. The research is aimed to increase knowledge of the effect of a static electric field on the plant growth process, because understanding of the topic is still limited. The plants were grown on a viscose substrate in a dark room without any light. Studies have shown that the electric field can affect the germination and growth process depending on the plant species. The findings indicate a positive influence of the electric field on radish germination. The presence of the electric field accelerates the germination process and growth of young plants. On the first day of germination (the 3rd day of cultivation), about 3.2 times as many plants germinated in the samples exposed to a stationary electric field compared to the control samples. On the last day of the experiment (the 8th day of cultivation), the tallest plants in the samples subjected to the electric field were 8 % higher, compared to the tallest plants in the control samples. On the other hand, the results demonstrate a negative impact of the electric field on oat seed germination. The presence of an electric field delays the germination process and reduces the number of germinated seeds. On the last day of the experiment (the 11th day of cultivation), about 1.25 times fewer oat plants germinated in the samples exposed to a stationary electric field compared to the control samples. The tallest plants in the samples subjected to the electric field were 1.1 times smaller than the tallest plants in the control samples.

The tendency of aerosols to carry viral particles featured significantly in public discourse during the SARS Covid-19 pandemic. In this research, the potential significance of the aerosol electric charge, especially as it relates to indoor relative humidity (RH) is considered. While electrostatic interactions may occur at any level of humidity, the level of humidity has a strong influence on these interactions. Above 55 % RH, there is sufficient moisture in the air to facilitate neutralization of the electric charges of particles and surfaces, whereas, at lower humidity levels, less moisture and higher surface resistivities enable increasingly stronger electrostatic interactions. Experiments were designed and conducted to study the behavior of electrically charged aerosols in fields emanating from capacitive touchscreens and permanent magnets. These preliminary experimental results suggest that operating indoor environments closer to the 55–60 % RH range could reduce interactions between these charged aerosols and capacitive touchscreens. This relative humidity range is within the acceptable ranges of humidity recommended by ASHRAE standard 55 which defines thermal environmental conditions for human occupancy.

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.%).