No abstract

The calculation was made for open DC electric arc burning in an external uniform axial magnetic field. It was performed within the framework of a nonstationary three-dimensional mathematical model in approximation of partial local thermodynamic equilibrium of plasma. A “schematic” analog of electron temperature fluctuations was proposed for numerical realization of the open electric arc column of a helical shape. According to calculations, it was established that the column of the open electric arc takes a helical space shape. Plasma rotates around a longitudinal axis of the arc, at that the directions of plasma rotation near the cathode and the anode are opposite. In the arc cross-sections, the velocity of plasma rotation is unequal and the deviation value of the same part of the arc from the central axis varies in time. A helical shape of the open arc is not stable and varies in time. Apparently, the open arc cannot remain stable and invariable in the time helical shape in the external axial magnetic field.

No abstract

A numerical simulation was performed for an open direct current (dc) electric arc in a uniform external axial magnetic field. The calculation was carried out in the frameworks of a non-stationary three-dimensional mathematical model in approximation of partial local thermodynamic equilibrium of plasma. The model does not presuppose a helical shape of the arc, as is customary in theoretical studies based on linear perturbation theory. It was shown that the helical shape of an open arc is not constant in time and periodically collapses with subsequent restoration. In a certain range of external parameters of the arc (current strength, inter-electrode distance, and external axial magnetic field), a new mode of destruction of a regular structure was revealed – the arc section shunting between the spiral turns. Shunting can be single or double when the breakdown occurs simultaneously in two places. Apparently, it is caused by convective heat transfer by plasma flows as well as by the sliding of the arc thermal field. The appeared thermal field creates a zone of electric conductivity in which the breakdown occurs.

Within the frameworks of non-stationary three-dimensional mathematical model, in approximation of a partial local thermodynamic equilibrium, a numerical calculation was made of characteristics of DC electric arc burning in a cylindrical channel in the uniform external axial magnetic field. The method of numerical simulation of the arc of helical shape in a uniform external axial magnetic field was proposed. This method consists in that that in the computational algorithm, a “scheme” analog of fluctuations for electrons temperature is supplemented. The “scheme” analogue of fluctuations increases a weak numerical asymmetry of electrons temperature distribution, which occurs randomly in the course of computing. This asymmetry can be “picked up” by the external magnetic field that continues to increase up to a certain value, which is sufficient for the formation of helical structure of the arc column. In the absence of fluctuations in the computational algorithm, the arc column in the external axial magnetic field maintains cylindrical axial symmetry, and a helical form of the arc is not observed.