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Modelling of low-current gas discharges by means of stationary solvers
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Abstract(s)
Este trabalho È dedicado ‡ modelizaÁ„o da igniÁ„o de descargas autÛnomas de baixa
corrente, e de caraterÌsticas tens„o-corrente mÈdias de descargas de coroa.
Foi desenvolvida uma abordagem para simulaÁ„o de descargas quasi-estacion·rias
de baixa corrente, sendo aplic·vel para descargas DC e tambÈm de baixa frequÍncia.
Esta abordagem colmata a lacuna entre os mÈtodos modernos de modelizaÁ„o numÈrica
e as abordagens de engenharia, e foi implementada como parte de um modelo numÈrico
que simule as descargas referidas em ar de alta press„o. O modelo inclui equaÁıes de
conservaÁ„o e transporte de espÈcies carregadas e a equaÁ„o de Poisson. Utiliza-se
um modelo cinÈtico ímÌnimoíde processos quÌmicos no plasma, em descargas de baixa
corrente em ar de alta press„o, que tem em conta os eletrıes, uma espÈcie eÖcaz de iıes
positivos, e os iıes negativos s O
This work is dedicated to modelling of ignition of self-sustaining low-current discharges and time-averaged characteristics of corona discharges. An approach for simulation of low-current quasi-stationary discharges has been developed, being applicable not only to DC but also to low-frequency discharges. Such approach bridges the gap between modern methods of numerical modelling and engineering approaches, and it has been implemented as a part of a numerical model of low-current quasi-stationary discharges in high-pressure air, The model comprises equations of conservation and transport of charged species and the Poisson equation. A íminimalí kinetic model of plasmachemical processes in low-current discharges in high-pressure air is used, which takes into account electrons, an e§ective species of positive ions, and negative ions The implementation of the numerical model is based on the use of stationary solvers, which o§er important advantages in simulations of quasi-stationary discharges. The developed model has been validated against experimental data over a wide range of conditions, and has been applied to several problems of high scientiÖc and technological interest. Firstly, the inception of discharges in high-pressure air has been investigated over a wide range of conditions.The method developed can be used as a predictor of the hold-o§ voltage in high-voltage devices, as well as to evaluate the sensitivity of the ignition voltage with respect to di§erent factors (the kinetic scheme used, the photoionization, and the secondary electron emission from the cathode). The second problem that has been studied was the e§ect that anode surface protrusions can have on pre-breakdown discharges in high-pressure air, which can be considered as an indirect evidence of the possible existence of microprotrusions on the electrode surface. The third problem concerned investigation of characteristics of DC corona discharges in a wide range of currents and gap widths. It is shown that computed inception voltages are in good agreement with experimental data. Anode microprotrusions with heights of the order of 50 m yield qualitative agreement with the experiment in all the cases. It is also shown that the calculated current-voltage characteristics are in good agreement with the measured data, and that stationary solvers allow decoupling of physical and numerical stability and reduction of computation time.
This work is dedicated to modelling of ignition of self-sustaining low-current discharges and time-averaged characteristics of corona discharges. An approach for simulation of low-current quasi-stationary discharges has been developed, being applicable not only to DC but also to low-frequency discharges. Such approach bridges the gap between modern methods of numerical modelling and engineering approaches, and it has been implemented as a part of a numerical model of low-current quasi-stationary discharges in high-pressure air, The model comprises equations of conservation and transport of charged species and the Poisson equation. A íminimalí kinetic model of plasmachemical processes in low-current discharges in high-pressure air is used, which takes into account electrons, an e§ective species of positive ions, and negative ions The implementation of the numerical model is based on the use of stationary solvers, which o§er important advantages in simulations of quasi-stationary discharges. The developed model has been validated against experimental data over a wide range of conditions, and has been applied to several problems of high scientiÖc and technological interest. Firstly, the inception of discharges in high-pressure air has been investigated over a wide range of conditions.The method developed can be used as a predictor of the hold-o§ voltage in high-voltage devices, as well as to evaluate the sensitivity of the ignition voltage with respect to di§erent factors (the kinetic scheme used, the photoionization, and the secondary electron emission from the cathode). The second problem that has been studied was the e§ect that anode surface protrusions can have on pre-breakdown discharges in high-pressure air, which can be considered as an indirect evidence of the possible existence of microprotrusions on the electrode surface. The third problem concerned investigation of characteristics of DC corona discharges in a wide range of currents and gap widths. It is shown that computed inception voltages are in good agreement with experimental data. Anode microprotrusions with heights of the order of 50 m yield qualitative agreement with the experiment in all the cases. It is also shown that the calculated current-voltage characteristics are in good agreement with the measured data, and that stationary solvers allow decoupling of physical and numerical stability and reduction of computation time.
Description
Keywords
Descargas de baixa corrente quasi-estacionárias Descargas de coroa Ignição de descarga autónoma Solvers estacionários Caraterísticas de coroa DC Low-current quasi-stationary discharges Corona discharges Ignition of self-sustaining discharge Stationary solvers Characteristics of DC corona Physics . Faculdade de Ciências Exatas e da Engenharia