No abstract

The effect of the cathode geometry on the characteristics of an electric arc is treated. It is found that the characteristics of plasma in discharges with cathodes of different geometry (cone, sphere, cylinder) are almost the same on condition of equality of the areas of current-conducting surfaces. It is assumed that a ring-shaped arc discharge may be realized in the case of axisymmetric arc spot on the external side surface of a cylindrical cathode.

The two-dimensional mathematical model in the approximation of a partial local thermodynamic equilibrium of plasma and the technique for numerical computation of the unsteady electric arc characteristics, including the conjugate heat exchange of the electric-arc plasma flow with the treated product (anode) are considered. The results of overall testing of the numerical algorithm point to the correctness of the model and computational technique. The results of the computation of the arc characteristics from the conventional ignition moment until the passage to stationary regime are presented. It is found that a single thermal torus, which scatters fairly quickly in the ambient medium, forms around the arc column.

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.

Some features are treated which are characteristic of a flow of arc plasma in the vicinity of a profiled cathode surface. Comparison of theoretical and experimental results leads one to assume that the formation of a plasma circulation zone in the vicinity of a profiled cathode surface contributes to reducing the erosion of the cathode material.