Manipulation of micrometer dielectric particles using traveling and standing electrostatic waves - Theoretical, experimental and numerical studies

Les convoyeurs électrostatiques à ondes progressives (COP) et stationnaires (COS) se présentent comme des moyens avantageux pour manipuler et transporter efficacement des particules sur une surface. L’objectif de cette thèse est d’étudier le comportement de particules diélectriques micrométriques sur ces systèmes. Les études expérimentales commencent par la caractérisation granulométrique et optique des particules et l’analyse de leur charge. Ensuite, l’efficacité de déplacement des particules par les deux types de convoyeurs est étudiée dans différentes conditions. Par ailleurs, les trajectoires des particules sont visualisées en utilisant une caméra ultra rapide. Un post-traitement des images obtenues en utilisant la vélocimétrie par suivi de particules (PTV) est mené pour calculer et étudier la vitesse des particules en fonction de différents paramètres. Les études théoriques et numériques menées avaient pour objectif d’étudier les ondes du potentiel électrique, la variation spatio-temporelle du champ électrique, et le bilan des forces mises en jeu. La dernière partie concerne la modélisation des trajectoires et le calcul numérique de la vitesse moyenne, ainsi que de la distance de déplacement des particules. Les résultats obtenus par modélisation sont en accord avec les observations et les calculs expérimentaux. Plusieurs modes de mouvement sont obtenus en fonction de la fréquence, la tension, la charge et la taille des particules. Les particules sont transportées plus efficacement dans le COP lorsqu’elles sont en mode synchrone sautillant. L’augmentation du nombre de phases permet à la fois de minimiser l’effet des ondes harmoniques inverses et d’augmenter la vitesse de propagation de l’onde directe ; cela mène à un déplacement plus rapide et plus loin des particules dans une seule direction, ce qui augmente l’efficacité du système.Traveling and standing wave electrostatic conveyors (TWC and SWC) are presented as advantageous techniques to effectively manipulate and transport particles on a surface. The aim of this work is to study the behavior of micrometer particles on these systems. Experimental studies begin with granulometric and optical characterization of particles and the measurement of their charge. Then, the particles displacement efficiency in both types of conveyors is studied under different conditions. In addition, the trajectories of the particles are visualized using high speed camera. The post-processing of the obtained images using Particle Tracking Velocimetry technique (PTV) is carried out to calculate and study the particles mean velocity and how it is affected by different parameters. The theoretical and numerical studies carried out aim to study the electric potential waves, the spatial and temporal variation of the electric field and the balance of the forces acting on particles. The last part concerns the modeling of particles trajectories and the numerical computation of their average velocity and displacement distance. The results obtained by modeling are in good agreement with the experimental observations and calculations. Several modes of movement are obtained depending on frequency, applied voltage value, as well as particle charge and size. Particles are transported more efficiently in the TWC when they are in synchronous hopping mode. Increasing the number of phases can minimize the effect of the backward harmonic waves and increase the speed of propagation of the forward wave that may help the particles to move faster and farther in one direction and lead to better displacement efficiency

Manipulation de particules diélectriques micrométriques par ondes électrostatiques progressives et stationnaires - Études théorique, expérimentale et numérique

Traveling and standing wave electrostatic conveyors (TWC and SWC) are presented as advantageous techniques to effectively manipulate and transport particles on a surface. The aim of this work is to study the behavior of micrometer particles on these systems. Experimental studies begin with granulometric and optical characterization of particles and the measurement of their charge. Then, the particles displacement efficiency in both types of conveyors is studied under different conditions. In addition, the trajectories of the particles are visualized using high speed camera. The post-processing of the obtained images using Particle Tracking Velocimetry technique (PTV) is carried out to calculate and study the particles mean velocity and how it is affected by different parameters. The theoretical and numerical studies carried out aim to study the electric potential waves, the spatial and temporal variation of the electric field and the balance of the forces acting on particles. The last part concerns the modeling of particles trajectories and the numerical computation of their average velocity and displacement distance. The results obtained by modeling are in good agreement with the experimental observations and calculations. Several modes of movement are obtained depending on frequency, applied voltage value, as well as particle charge and size. Particles are transported more efficiently in the TWC when they are in synchronous hopping mode. Increasing the number of phases can minimize the effect of the backward harmonic waves and increase the speed of propagation of the forward wave that may help the particles to move faster and farther in one direction and lead to better displacement efficiency.Les convoyeurs électrostatiques à ondes progressives (COP) et stationnaires (COS) se présentent comme des moyens avantageux pour manipuler et transporter efficacement des particules sur une surface. L’objectif de cette thèse est d’étudier le comportement de particules diélectriques micrométriques sur ces systèmes. Les études expérimentales commencent par la caractérisation granulométrique et optique des particules et l’analyse de leur charge. Ensuite, l’efficacité de déplacement des particules par les deux types de convoyeurs est étudiée dans différentes conditions. Par ailleurs, les trajectoires des particules sont visualisées en utilisant une caméra ultra rapide. Un post-traitement des images obtenues en utilisant la vélocimétrie par suivi de particules (PTV) est mené pour calculer et étudier la vitesse des particules en fonction de différents paramètres. Les études théoriques et numériques menées avaient pour objectif d’étudier les ondes du potentiel électrique, la variation spatio-temporelle du champ électrique, et le bilan des forces mises en jeu. La dernière partie concerne la modélisation des trajectoires et le calcul numérique de la vitesse moyenne, ainsi que de la distance de déplacement des particules. Les résultats obtenus par modélisation sont en accord avec les observations et les calculs expérimentaux. Plusieurs modes de mouvement sont obtenus en fonction de la fréquence, la tension, la charge et la taille des particules. Les particules sont transportées plus efficacement dans le COP lorsqu’elles sont en mode synchrone sautillant. L’augmentation du nombre de phases permet à la fois de minimiser l’effet des ondes harmoniques inverses et d’augmenter la vitesse de propagation de l’onde directe ; cela mène à un déplacement plus rapide et plus loin des particules dans une seule direction, ce qui augmente l’efficacité du système

Impact of spatial harmonic waves on dielectric particles displacement in standing and traveling wave electric fields

International audienceThe purpose of this work is to investigate the effect of spatial harmonic waves on dielectric particles displacement process using standing and traveling electric wave electric conveyors. This investigation is divided into two main parts. The first one is an experimental study, where the efficiency of conveyors for the displacement of micrometer sized PMMA particles is analyzed. The second part consists of a numerical and theoretical study in which the spatial electric potential distribution and the consequences on the spatial harmonics on particles displacement are investigated. The results show that the displacement efficiency and the particles direction depend basically on the particles size, the charge to mass ratio, the applied voltage and the frequency. In the standing wave conveyor, the particles move toward both right and left directions. In the traveling wave conveyor, at high voltage, low frequency, small particles or high charge to mass ratio conditions particles move toward the traveling wave direction. In the case of low applied voltage, high frequency or if the particles have a low charge to mass ratio, some particles move toward the opposite direction because of the backward harmonic wave that appears near to the surface. The magnitude of the harmonic waves depends on the levitation height of particles; it can be controlled by varying the number of phases, the gap spacing or the thickness of electrodes or by adding a dielectric barrier over the surface

Study of Discharge Inception and Propagation in Liquid–Solid Insulation System under DC–LI Superimposed Constraints

High-voltage direct current (HVDC) links are starting to become widely implemented thanks to their interesting advantages such as reduced operation losses, the absence of reactive power, which allows energy transport via underground cables over long distances, and improved power control. The latter advantage is very essential for renewable energy resource integration into power grids. However, a thorough understanding of the behavior of insulation systems for HVDC components is critical so as to ensure a more reliable service. Indeed, the existence of the direct current (DC) voltage in HVDC components may induce surface and space charge accumulation that can stress insulation further or even promote discharge inception and propagation. As such, this work focuses on showcasing the effect of surface charge on streamers that develop on the interface of liquid–solid insulation due to the advent of lightning impulse (LI) voltage in the HVDC link. This study was performed using finite-element-based numerical simulations that include a quasi-electrostatic model for surface charge accumulation and an electrohydrodynamic fluid model for streamer initiation and propagation. The geometry used was point–plane configuration where the high voltage is applied to the needle electrode located above the liquid–solid interface. The obtained results suggest that streamer initiation is affected by both the accumulated surface charge density and polarity. For a positive streamer, an accumulation of positive surface charge increases the discharge inception voltage as a result of a weakening in the electric field, while an accumulation of negative surface charge decreases the discharge inception voltage due to an intensification in the electric field. Moreover, streamer travel distance and velocity are also both shown to be affected by surface charge accumulation

Pockels Effect Based Electro-Optic Sensor for Partial Discharge Measurement in Medium and High Voltage Equipment

International audienceThe aim of the present work is to investigate the efficiency of electro-optic electric field sensor to characterize and detect the partial discharges in medium or high voltage equipment such as air or gas insulated switchgear. Partial discharges (PD) are frequently caused by an increase in the electric field surrounding conductors (metal particles, spikes, etc.) or at the level of cavities and cracks in solid insulators (cables, insulators, etc.). These phenomena cause gas ionization, heating, material physicochemical degradation, electromagnetic disturbances, and, as a result, premature aging of the insulation. Traditional measurement methods based on purely electrical techniques such as HFCT and UHF antennas allow a global measurement of partial discharges in the whole system. This work presents a study of Pockels effect based electro-optical sensors for partial discharge measurement under AC and DC voltage waveforms and compare their signals to those of traditional methods. Having no metallic parts, these sensors offer a local characterization of the discharge based on the induced local electric field variations

Study of Two-Stage-Type Electrostatic Precipitator in Axisymmetric Configuration Applied to Finely Ground Lignocellulosic Materials

The main objective of this paper is to develop a novel two-stage-type electrostatic precipitator to collect finely ground lignocellulosic particles. To prevent the danger of explosion of such a powdery material, ion generation and particle charging processes are separated. Main results show that the particles can be highly charged in a two-coaxial-cylinders triode-type device, which also facilitates their collection. For instance, the collection efficiency reaches 92% for particle size of about 0.3 μm, and exceeds 99% for particle size greater than 2 μm

Fine particle removal by a two-stage electrostatic precipitator with multiple ion-injection-type prechargers

International audienceA novel two-stage electrostatic precipitator (ESP) with multiple ion injection type chargers and parallel collection plates was developed and shown to efficiently collect particles from the corrosive waste gas discharged from semiconductor and optoelectronic processes. Multiple carbon brush electrodes for the generation of ions were located outside of the main gas flow, but the injection of clean air and induced voltage between the outer and inner plates of the charging stage carried ions into the main gas flow; thus, gases and particles in the main flow did not corrode or contaminate the charger. The particle collection performance of the ESP was evaluated experimentally for 0.3 μm particles, PM (Particular matter) 10, and PM 2.5 by varying the application voltages to the charging stage, main gas flow rate, and distance of the carbon brush discharge electrode from the main gas flow duct. The novel ESP achieved particle collection efficiency of 89.5% and 99.5% at the best condition when the voltage was applied to only the charging stage and to both the charging and collection stages, respectively. The particle collection efficiency of the charging stage only and the two-stage ESP was characterized according to the corona discharge power and main flow rate based on Deutsch's collection theory. Also, a simplified 2D simulation results show that the electric field is very high not only near outer carbon fibers but also near the outer metallic electrode edge