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The Use of Microwaves, Plasma and Laser for Wood Modification
Published in Dick Sandberg, Andreja Kutnar, Olov Karlsson, Dennis Jones, Wood Modification Technologies, 2021
Dick Sandberg, Andreja Kutnar, Olov Karlsson, Dennis Jones
In addition to this “direct” chemical activation of the wood surface, two “indirect” activation methods have emerged: the use of a corona discharge and of plasma modification. A corona discharge is a process whereby current passes from an electrode with a high potential into a neutral fluid, usually air, and causes the fluid (air) to ionise, generating a plasma around the electrode. The ions generated pass to nearby areas of lower potential (such as a wooden surface), pass the charge to nearby areas of low potential or recombine to form neutral gas molecules. More recently, plasma treatment has come to replace corona treatment, mainly because of the low intensity often associated with a corona discharge, which can have only a limited impact on the surface. It is technically possible to increase the energy of the corona discharge, but this would increase the temperature of the wood being treated and this might have an undesirable effect.
Testing Techniques
Published in Mazen Abdel-Salam, Hussein Anis, Ahdab El-Morshedy, Roshdy Radwan, High-Voltage Engineering, 2018
A new equipment may pass a high-voltage test but may fail in the same test after some time in service. This is due to contamination of the insulators’ surfaces, which can lower their dielectric strength while gradual chemical deterioration due to the reaction of the insulation with air is taking place. Corona discharges in voids in the insulation can gradually cause deterioration (Chapter 8). Voltage transients can initiate tracking or carbonization, and can even puncture the insulation and lead to early failure. This shows the importance of periodic maintenance and in-service tests. The following sections are devoted to various types of tests and voltages to be applied to circuit breakers, cables, transformers, high-voltage insulators, and surge arresters.
Numerical Computation of Electric Field
Published in Sivaji Chakravorti, Electric Field Analysis, 2017
It is well known that the withstand voltage of the external insulation of apparatus designed with non-self restoring insulation is determined by the maximum value of electric field intensity within the insulation system. Further, corona discharges are eliminated by proper design of highvoltage shielding electrodes. Thus, a comprehensive study of the electric field distribution in and around high-voltage equipment is of great practical importance.
Optimizing singly-charged electrosprayed particle throughput of an electrospray aerosol generator utilizing a corona-based charger
Published in Aerosol Science and Technology, 2022
Muhammad Miftahul Munir, Widya Sinta Mustika, Casmika Saputra, Martin Adrian, Asep Suhendi
Most neutralizers utilize radioactive ionizers to produce bipolar ions. However, radioactive sources have always met legal restrictions (Mustika et al. 2021; Saputra et al. 2021; Qi and Kulkarni 2013; Kwon et al. 2005). A neutralizer based on a corona discharge can solve this problem. Corona discharge is a plasma that occurs as a relatively low-power electrical discharge at or near atmospheric pressure (Romay, Liu, and Pui 1994; Whitby and Peterson 1965). Corona discharge has been proposed to reduce the charges of electrosprayed particles (Laschober et al. 2006; Lu and Koropchak 2004; Ijsebaert et al. 2001; Ebeling et al. 2000; Meesters et al. 1992). However, there is little literature investigating the charge reduction performance of neutralizers in the EAG system. Laschober et al. (2006) reported that for nanosized particles, a unipolar corona charger could be used as a neutralizer in a commercial EAG. Unipolar corona discharge acquires a charge distribution that significantly depends on ion properties and abundance, flow/residence time variation, the preexisting charge on particles, and particle properties (Qi and Kulkarni 2013). Thus, more work is needed to minimize multiply charged particles (Laschober et al. 2006). Therefore, a bipolar charger is required for creating a bipolar environment in the charge reduction process. The bipolar charger can reduce multiple charges (Qi and Kulkarni 2013).
Partial Discharge Detection and Localization in Power Transformers based on Acoustic Emission: Theory, Methods, and Recent Trends
Published in IETE Technical Review, 2021
Viral B. Rathod, Ganesh B. Kumbhar, Bhavesh R. Bhalja
Four types of partial discharge defects are shown in Figure 1 [2]. Internal Discharges: It occurs in voids or cavities within the solid or liquid insulating material.Surface Discharges: It appears at the boundary of the different insulating materials.Corona Discharges: It occurs due to the non-uniform (inhomogeneous) electric fields at the sharp points of the electrodes under high voltage either in air, liquid, or other gaseous insulating material.Treeing: It occurs due to the continuous impact of discharges in the solid insulating material, which forms a conducting channel.
Discharge electrode geometry and energy efficiency in a one-stage wire–tube electrostatic precipitator operating at high concentrations of submicron liquid aerosol
Published in Environmental Technology, 2020
Christian Bacher, Volodymyr Lebedynskyy, Silvio Fischer, Ulrich Riebel
One of the most efficient devices to control particle emissions is the electrostatic precipitator (ESP). Particle removal by ESPs proceeds in four consecutive steps: (i) positive or negative gas ions are produced depending on the polarity of a corona discharge. Typically, the corona discharge is produced by applying a high voltage to a discharge electrode with a small radius, which is surrounded by a grounded precipitation electrode having a larger radius of curvature. The resulting inhomogeneous electric field distribution produces a continuous gas discharge without electric breakdown, which is also referred to as active electric field. For cylindrical wire–tube ESPs, the field strength required for corona discharge can be calculated from an empirical equation given by White [1]. (ii) The ions transfer their charge to the aerosol particles by the mechanisms of field charging (dominating for particles >1 µm) and diffusion charging (dominating for particles <0.1 µm) [2]. (iii) In the electrostatic field, the charged particles drift towards the precipitation electrode, where they deposit on the electrode surface before (iv) being cleaned off. In dry ESPs, this is mostly done by rapping. In wet ESPs, the precipitation electrode is cleaned by flushing with a liquid or a continuous falling film over the electrode surface. For liquid particles, their self-draining nature requires less frequent or no additional flushing at all [3].