Theoretische Beschreibung und Modellierung von Lichtbögen bei kleinen Strömen und kleinen Elektrodenabständen
Zusammenfassung der Projektergebnisse
The project was aimed at non-equilibrium description and modelling of low-current electric arcs of short length involving the interaction with the electrodes. Questions of fundamental importance related to the spatial structure of the arcs were to be clarified. The non-equilibrium modelling of low-current and short-length arcs was done on two levels. The first one, denoted as the fully non-equilibrium model (FNEM), employed a fully non-equilibrium magnetohydrodynamic description of the quasineutral arc column along with the heat and current transfer in the electrodes. The regions of space charge adjacent to the electrodes were taken into account in the boundary conditions. The second modelling level, denoted as the unified non-equilibrium model (UNEM), employed a unified non-equlibrium description of the entire inter-electrode region, in which no assumption of quasineitrality was done. The modelling results were accomplished by experiments. The FNEM was applied in two spatial dimensions to a tungsten-inert-gas configuration in atmospheric pressure argon. Modelling predictions were compared with experimental results for wide regions of variation of the arc length and the arc current. The arc length was reduced to below 1 mm for an arc current of about 5 A. The results showed that at low arc current the convection effects and the selfinduced magnetic field were of minor importance. These findings offered the opportunity for simplifications and were used in the development of the unified non-equilibrium model. The UNEM was applied in one and two spatial dimensions for tungsten-inert gas configurations, whereby the one-dimensional model showed a high computational efficiency and applicability to multicomponent arc plasma. This model was capable of predicting the transition from the glow to the arc regime of the discharge in atmospheric pressure argon. Thereby, the self-consistent heating of a tungsten cathode by the plasma was implemented. The spatial extent of the regions of space charge was determined for a wide region of values of the current density. The microdischarge was operated in arc regime even for a gap length of only 15 µm, for which a quasineutral part of the plasma did not exist. At lower current densities, the gap length corresponding to a fully non-quasineutral plasma increases. The predicted voltage increases at a given current density with the decrease of the gap length in agreement with experimental observations. The self-consistent coupling of the plasma with the electrodes further allowed us to study a switching arc configuration under conditions at which a phase change in the electrodes occurred. A melting and a release of copper atoms from a copper anode and a copper cathode was considered. Additional challenges in the case of a non-refractory cathode was the implementation of the thermo-field emission of electrons from the non-refractory cathode and the collisional-radiative model of the metal vapour released into the plasma. To the best of our knowledge, this is the first report on such a model. Results of the two non-equilibrium approaches were compared with each other and with experimental findings. The predicted characteristics (arc voltage, temperatures, emission spectra) were found to agree well with measured values. The FNEM becomes inapplicable when the quasineutral arc column vanishes and the regions of space charge merge. This occurs for gap lengths of a few 10 µm, whereby the assumption of quasi-neutrality fails and the solution of the Poisson’s equation becomes unavoidable. The applicability of the UNEM as a fluid model is limited to gap lengths, which exceed the mean free path of the electrons. The modelling approaches developed in the framework of this project provide a basis for important technological applications such as the short and micro arc welding, generative manufacturing with arc welding devices, and the development of low-voltage contacts and switching devices as a part of indispensable industrial and customers’ applications. The UNEM applied to plasma between copper or composite electrodes can improve the description of the arc attachment in low-voltage switching devices, where semi-empirical relations are still employed. This will provide a deep insight into the processes that determine the immobility time of the arc attachment in these devices. The arc immobility time is amid the main factors delaying an effective voltage rise and reducing the switching performance.
Projektbezogene Publikationen (Auswahl)
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Fluid modelling of DC Argon Microplasmas: Effects of the electron transport description, Plasma Chem. Plasma Process., Vol. 39, 2019, pp. 949-968
Baeva, M.; Loffhagen, D.; Becker, M. M.; Uhrlandt, D.
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Unified non-equilibrium modeling of tungsteninert gas microarcs in atmospheric pressure argon, Plasma Chem. Plasma Process., Vol. 39, 2019, pp. 1359-1378
Baeva, M.; Loffhagen, D.; Uhrlandt, D.
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Plasma parameters of microarcs towards minuscule discharge gap, Contributions to Plasma Physics, Vol. 60, 2020, e202000033
Baeva, M.; Loffhagen, D.; Becker, M. M.; Siewert, E.; Uhrlandt, D.
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Unified modelling of non-equilibrium microarcs in atmospheric pressure argon: potentials and limitations of one-dimensional models in comparison to two-dimensional models, Jap. J. Appl. Phys., Vol. 59, 2020, SHHC05
Baeva, M.; Uhrlandt, D.; Loffhagen, D.
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Unified modelling of low-current short-length arcs between copper electrodes, J. Phys. D: Appl. Phys. Vol. 54, 2021, pp. 025203
Baeva, M.; Boretskij, V. F.; Gonzalez, D.; Methling, R.; Murmantsev, O.; Uhrlandt, D.; Veklich, A
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Unified modelling of TIG microarcs with evaporation from copper cathode, Plasma Phys. Technol. Vol. 8, 2021, pp. 1-4
Baeva, M.; Methling, R., Uhrlandt, D.
