After a brief history of plasma arc cutting (PAC) is given, its types and abilities are discussed. Experimental data (unfortunately, little is available) on plasma parameters are reviewed. The status of contemporary understanding of the process involved in PAC is presented. The main emphasis is on those processes that determine the technological abilities of the method. Along with the existing theories reviewed, we propose qualitative hypotheses on some of these processes. Among them are: dependence of the cyclic cathode erosion on the rate of current increase, double arcing and the role of insulating inclusions at the nozzle orifice on double arcing, dross formation and the shape of the kerf.

Atmospheric pressure arcs have recently found application in the production of nanoparticles. Distinguishing features of such arcs are small length and hot ablating anode characterized by intensive electron emission and radiation from its surface. We performed one-dimensional modeling of argon arc, which shows that near-electrode effects of thermal and ionization non-equilibrium play important role in operation of a short arc, because the non-equilibrium regions are up to several millimeters long and are comparable with the arc length. The near-anode region is typically longer than the near-cathode region and its length depends more strongly on the current density. The model was extensively verified and validated against previous simulation results and experimental data. Volt-Ampere characteristic (VAC) of the near-anode region depends on the anode cooling mechanism. The anode voltage is negative. In case of strong anode cooling (water-cooled anode) when anode is cold, temperature and plasma density gradients increase with current density resulting in decrease of the anode voltage (absolute value increases). Falling VAC of the near-anode region suggests the arc constriction near the anode. Without anode cooling, the anode temperature increases significantly with current density, leading to drastic increase in the thermionic emission current from the anode. Correspondingly, the anode voltage increases to suppress the emission -and the opposite trend in the VAC is observed. The results of simulations were found to be independent of sheath model used: collisional (fluid) or collisionless model gave the same plasma profiles for both near-anode and near-cathode regions.Parametric studies of short atmospheric pressure argon arc with tungsten electrodes were performed for various current densities and inter-electrode gap sizes. Non-equilibrium effects in the near-electrode regions were studied. Anodes with and without water cooling were considered. Effect of electron emission on current-voltage characteristic of the near-anode layer was investigated. Analytical formulas for scaling of non-equilibrium regions widths and Volt-Ampere's characteristics of these regions and the whole arc are given in the accompanying paper 44 .The organization of the paper is as follows. In Section II governing equations and boundary conditions for plasma and electrodes are presented. Section III describes numerical procedure of solving the governing equations. Results of simulations including validation of the model and parametric studies of the arc are presented and discussed in Section IV. Conclusions of this work are summarized in Section V.

The thermoelectric figure of merit is calculated for a compound material comprising thin semiconductor and wider metallic layers. The layers are perpendicular to the direction of current. The semiconductor barriers exclude electrons with energies ε<μ from the current. This exclusion increases thermopower. One may obtain a material with a very high ZT if the distance between the barriers is on the order of the energy relaxation length. This material should have the resistivity characteristic of a metal and the thermopower characteristic of a semiconductor. An additional significant rise in ZT can be achieved by increasing the contact area at the metal–semiconductor interface.

A simple model describing the plasma temperature, pressure and velocity distributions inside the nozzle during plasma arc cutting is developed. Temperature dependences of plasma properties are considered. Predicted and measured values of the plasma pressure inside the arc chamber are compared to validate the model. Calculations demonstrated that a substantial portion of the power dissipated inside the nozzle is radiated; the rest heats the plasma jet. The proportion of the power lost due to radiation increases with the arc current, length of the nozzle and gas-flow rate. The double-arcing phenomenon is hypothesized to result from the electrical breakdown of the gas at the nozzle's exit. Calculations of the electrical field at the nozzle's exit support this hypothesis.

The main forces acting on the molten tip of an arc electrode are surface tension and electromagnetic force. Both of these forces depend on the shape of the droplet. Conversely, the shape of the droplet is determined by these forces. The equation to describe the shape of the droplet pending at the arc electrode is proposed and solved. This allows calculating the size of the detaching droplet significantly more accurately and over a wider current range compared to both existing models (stable force balance theory and pinch instability theory). Furthermore, the equation describes the main changes of the metal transfer as the arc current increases: slow decrease of the droplet size at low currents, sharp decrease at higher currents, and absence of the stable droplet above a certain current value. For higher currents a simple non-stationary model of the droplet development is proposed.