FEM-FCT Based Dynamic Simulation of Trichel Pulse Corona Discharge in Point-Plane Configuration

In this thesis, a new two-dimensional numerical solver is presented for the dynamic simulation of the Trichel pulse regime of negative corona discharge in point-plane configuration. The goal of this thesis is to simulate the corona discharge phenomenon and to improve the existing models so that the results have an acceptable compatibility with the experimentally obtained data. The numerical technique used in this thesis is a combination of Finite Element Method (FEM) and Flux Corrected Transport (FCT). These techniques are proved to be the best techniques, presented so far for solving the nonlinear hyperbolic equations that simulate corona discharge phenomenon. The simulation begins with the single-species corona discharge model and thedifferent steps of the numerical technique are tested for this simplified model. The ability of the technique to model the expected physical behaviour of ions and electric field is investigated. Then, the technique is applied to a more complicated model of corona discharge, a three-specie model, in which three ionic species exist in the air gap: electrons, and positive and negative oxygen ions. Avalanche ionization, electron attachment and ionic recombination are the three ionic reactions which this model includes. The macroscopic parameters i.e., the average corona current and the Trichelpulses period are calculated and compared with the available experimental data. The technique proves to be compatible with the available experimental results. Finally, the effects of different parameters on the Trichel pulse characteristics are investigated. The results are further compared against the available experimental data for the effect of pressure on Trichel pulse characteristics and are reported to be compatible

Numerical and Experimental Study of the Trichel Pulses in Needle-plane Geometry

One of the unique aspects of the negative corona discharges in the air is the regular train of pulses that form the discharge current, called Trichel pulses. These pulses are the result of the combination of several phenomena such as the avalanche ionization of the neutral molecules by the impact of the energized electrons, formation of the cloud of positive ions close to the cathode, and formation of the cloud of negative ions at a farther distance from the corona electrode compared to their positive counterparts. In this thesis, the results of a detailed numerical investigation of the formation of Trichel pulses in a needle-plane negative corona discharge, as well as a simulation of the transition of the discharge from Trichel pulse regime to the glow discharge regime, is presented. All presented numerical models in this thesis were three-species models including the motion, generation, and dissipation of three charged species: electrons, positive ions, and negative ions. Also, all models were built using COMSOL multiphysics. Photoionization as the main mechanism for sustaining the positive corona discharge was included in the numerical analysis for both the positive and negative corona discharges using the three exponential approximation. A parametric study of the impact of different model coefficients on the characteristic of the Trichel pulses including the repetition frequency, average DC current and pulse rise time was investigated. The studied parameters include coefficients of the two ionization, and attachment reactions, the mobilities of the three charged species considered, electrons, positive ions, and negative ions, and the coefficient of the secondary electrons emitted from the needle. It was shown that two reactions, the recombination of positive and negative ions, and the recombination of electrons and positive ions play a minor role in the calculated characteristics of the Trichel pulses. Finally, an experimental study of the characteristics of the Trichel pulses in air at room temperature, pressure, and relative humidity has been conducted. The impact of different parameters: the needle voltage, needle-plane distance and the radius of curvature of the needle’s tip on the frequency, DC current, and the temporal characteristics of the pulses (rise time, fall time, and the pulse width) was studied. Four different needles with radii of curvature ranging from 19 to 55 microns were used. Applied voltage on the needle was varied from the onset voltage (-4 kV to -6 kV) to -10 kV. It was observed that the temporal characteristics of the pulses such as rise time, was not a function of needle tip radius of curvature, voltage level, or needle-plane distance. The experimental data were compared with the results of a numerical simulation. The experimental findings were in a good agreement with the results of the numerical model

Simplified Numerical Models in Simulating Corona Discharge and EHD Flows

Corona discharge is used in many practical applications. For designing and optimization of corona devices, the discharge phenomenon should be numerically simulated. Most often, the corona discharge model is simplified by neglecting the process dynamics and assuming a limited number of reactions and species. In the extreme case, monopolar corona models with just one species and no reactions are studied. However, there is a problem with determining boundary conditions for the space charge density. The simplest solution to this problem was suggested by Kaptzov, who hypothesized that the electric field on the electrode surface remains constant and equal to the value at the onset conditions, which is known from a semi-empirical Peek’s formula. Experimental data confirm good accuracy of this approach. However, it is impossible to experimentally measure the surface electric field at different voltage levels and compare it to Peek’s value. Our thesis will discuss different methods for simulating corona discharge in 1D wire-cylinder geometry in air at atmospheric pressure. The classical model based on Kaptzov’s hypothesis is compared with other approaches. The first model is still a single-species one, but it uses direct ionization criterion. Two other models consider a higher number of species and some number of reactions, so the ionization layer is included. The surface electric field can differ from Peek’s value by almost 43%. In addition, the results of numerical investigations of the EHD flow generated by dc corona discharge in the point-plane configuration in atmospheric air are presented in this thesis. A computational model of the discharge includes the ionization layer and three ionic species. The most important ionic reactions (ionization, attachment, recombination and detachment) are considered. The results of the corona simulations were used to predict the secondary EHD flow. All flow parameters (velocity components, pressure, streamlines) are determined. In addition to main flow vortex reported before, a local vortex near the discharge tip has also been discovered. COMSOL, a commercial finite element package, was used in simulations

KRYTYCZNY PRZEGLĄD MODELI UŻYWANYCH W SYMULACJI NUMERYCZNEJ ELEKTROFILTRÓW

The electrostatic precipitators (ESP) have been drawing more and more attention due to their high efficiency and low costs. Numerical simulation is a powerful, economical and flexible tool to design ESP for industry applications. This review summarizes the available numerical models to simulate different physical processes in ESP, including ionized electric field, air flow, particle charging and motion. It has been confirmed that the available models could provide acceptable results and the computing requirements are affordable in industry applications. The coupling between different physical processes can also be considered in simulation. However, there are still some problems not solved, such as selection of a suitable turbulence model in EHD simulation and the coupling criteria. The future study should focus on these issues. This review also includes new types of ESP developed in recent years, such as dielectric barrier discharge (DBD) ESP and corona assisted fibrous filter. These new types of ESP have had high efficiency and low energy consumption. Even though nearly all new ESP types can be modeled using the available numerical models, the most challenging issue is the DBD simulation.Elektrofiltry są obiektem nieustającej uwagi ze względu na ich wysoką sprawność i niski koszt. Symulacja numeryczna jest bardzo skutecznym, ekonomicznym i elastycznym narzędziem przy projektowaniu przemysłowych elektrofiltrów. Ten artykuł podsumowuje dostępne modele numeryczne do symulacji różnych procesów fizycznych występujących w elektrofiltrach, włączając zjonizowane pole elektryczne, przepływ powietrza, ładowanie cząstek i ich trajektorie. Zostało potwierdzone, że dostępne modele mogą dostarczyć zadowalających wyników nawet używając sprzętu komputerowego dostępnego w zastosowaniach przemysłowych. Wzajemne sprzężenia między różnymi procesami fizycznymi mogą być analizowane podczas symulacji. Ciągle istnieją jednak problemy nierozwiązane, na przykład wybór odpowiedniego modelu turbulencji przeplywu gazu albo kryteriów sprzężeń. Przyszłe badania powinny skoncentrować się na ich rozwiązaniu. Ten przegląd omawia też nowe rodzaje elektrofiltrów zaproponowanych w ostatnich latach, na przykład elektrofiltry oparte na wyładowaniach z barierą dielektryczną albo wspomagane wyładowaniem koronowym filtry włókniste. Te nowe typy elektrofiltrów mają wysoką sprawność i niski pobór energii. Jeśli nawet prawie wszystkie nowe typy elektrofiltrów mogą być modelowane z użyciem istniejących modeli numerycznych, najtrudniejsze jest modelowanie wyładowania z barierą dielektryczną

Secondary Electrohydrodynamic Flow Generated by Corona and Dielectric Barrier Discharges

One of the main goals of applied electrostatics engineering is to discover new perspectives in a wide range of research areas. Controlling the fluid media through electrostatic forces has brought new important scientific and industrial applications. Electric field induced flows, or electrohydrodynamics (EHD), have shown promise in the field of fluid dynamics. Although numerous EHD applications have been explored and extensively studied so far, most of the works are either experimental studies, which are not capable to explain the in depth physics of the phenomena, or detailed analytical studies, which are not time effective. The focus of this study is to provide the model that in a reasonable computational time is able to give us accurate results in different electric-fluid interactions. So, the main goals of this study is to provide a model to simulate all essential physical phenomena, applicable in different EHD systems. So, in this thesis, first, a two-dimensional numerical solver is presented for the dynamic simulation of the Dielectric Barrier Discharge (DBD) and the Corona Discharge (CD) in point to plane configuration. The simulations start with the single-species model and the different steps of the numerical technique are tested for this simplified model. The ability of the technique to model the expected physical behavior of ions and electric field is investigated. The studied physics were implemented in different geometry configurations such as wire to plane, wire to wire, and plane to plane geometries. The electrostatic field and ionic space charge density due to corona discharge were computed by numerically solving Poisson and current continuity equations, using a Finite Element method (FEM). The detailed numerical approach and simulation procedure is discussed and applied throughout the thesis. Then, the technique is applied to a more complicated model in order to address several existing EHD applications. The complicated mutual interaction between the three coexisting phenomena of electrostatic field, the charge transport, and fluid dynamics, which affect the EHD process, were taken into account in all the simulations. Calculations of the gas flow were carried out by solving the Reynolds-averaged Navier-Stokes (RANS) equations using FEM. The turbulence effect was included by using the k-ε model included in commercial COMSOL software. An additional source term was added to the gas flow equation to include the effect of the electrostatic body force. In all the simulations, the effects of different parameters on the overall performance of the system and its characteristics are investigated. In some cases, the simulation results were compared with the existing experimental data published in literature

Numerical studies of Electrohydrodynamic Flow Induced by Corona and Dielectric Barrier Discharges

Electrohyrodynamic (EHD) flow produced by gas discharges allows the control of airflow through electrostatic forces. Various promising applications of EHD can be considered, but this requires a deeper understanding of the physical mechanisms involved. This thesis investigates the EHD flow generated by three forms of gas discharge. First, a multiple pin-plate EHD dryer associated with the positive corona discharge is studied using a stationary model. Second, the dynamics of a dielectric barrier discharge (DBD) plasma actuator is simulated with a time-dependent solver. Third, different configurations of the extended DBD are explored to enhance the EHD flow. The results of the numerical simulations include the discharge current, space and surface charges, velocity profiles, EHD force and efficiency, which have been validated with the experimental data from collaborating researchers and those available in literature. This thesis provides a valuable insight into the physics of the EHD flow induced by gas discharge

Design of a high power ultra wideband system using a fast impulse current generator

This thesis presents a DC-Charged high amplitude electromagnetic radiator. The radiator consists of a Half Impulse Radiating Antenna (HIRA) fed by a coaxial Pulse Forming Line (PFL), which is charged using a mechanism based on corona currents on floating electrodes. The theoretical background, the design process, the construction and the experimental characterization of the radiated signals are presented and discussed. A circuit model of the corona charging mechanism is proposed and validated.Doctorad

Modélisation volumes-finis en maillages non-structurés de décharges électriques à la pression atmosphérique

La modélisation numérique des décharges plasma joue un rôle important dans la compréhension des mécanismes physiques ou chimiques ayant lieu dans les dispositifs assistés par plasma. Une grande partie de ces mécanismes est déjà prise en compte dans les codes actuels. En revanche, beaucoup d'entre eux ne permettent pas de travailler avec des géométries complexes. Cette limitation provient essentiellement de l'utilisation de maillages structurés, cartésiens. Ceux-ci ne sont pas bien adaptés aux géométries courbes. Les calculs en maillages structurés deviennent rapidement compliqués et spécifiques à une géométrie donnée. Notre travail concerne la modélisation de décharge pour un réacteur de traitement à la pression atmosphérique développé par Dow Corning. Sa configuration complexe ainsi que ses grandes dimensions nous ont incités à faire un nouveau code fonctionnant en maillages non structurés. Celui-ci doit être capable de s'adapter à la présence d'une pointe, d'arrondis et de multiples diélectriques mais aussi permettre le passage rapide à de nouvelles géométries. De plus ses grandes dimensions nécessitent l'utilisation de maillages raffinés uniquement aux endroits nécessaires (pointe, surfaces des diélectriques...). Le modèle mathématique utilisé est basé sur l'équation de Poisson couplée aux équations de transport de type dérive-diffusion. Plusieurs discrétisations numériques ont été testées dans des configurations physiques différentes. Nous présentons et validons les méthodes numériques choisies. Les résultats obtenus pour le réacteur Dow Corning sont alors exposés et commentés.The numerical modeling of plasma discharges plays an important role in understanding the physical or chemical mechanisms which occurs in plasma-assisted devices. Much of these mechanisms are already factored into current codes. However, many of them do not work with complex geometries. This limitation is mainly due to the use of structured grids, Cartesian grids. These are not well suited for curved geometries. Calculations in structured meshes quickly become complicated and specific to a given geometry. Our work concerns the modeling of electrical discharges produced by a treatment reactor at atmospheric pressure developed by Dow Corning. Its complex configuration and its size led us to a new code operating in unstructured meshes. The mathematical model is based on the Poisson equation coupled with the transport equations in the drift-diffusion approximation. Several numerical disretizations were tested in different physical configurations. We present and validate the chosen numerical methods. The results obtained in the reactor are then exposed and dicussed