Arc plasma torch

　　An arc plasma generator, also known as an arc plasma torch or a plasma spray gun, and sometimes referred to as an arc heater, is a discharge device capable of producing a directed “low‑temperature” (approximately 2,000 to 20,000 K) plasma jet.

　　Plasma torches, classified according to their arc‑plasma configuration, are divided into non-transferred‑arc torches and transferred‑arc torches. In a non‑transferred‑arc torch, the anode also serves as the torch nozzle; in a transferred‑arc torch, the anode refers to the workpiece to which the arc is transferred from the torch. Of course, there are also combined plasma torches that incorporate both transferred‑arc and non‑transferred‑arc modes.

　　Arc plasma is widely used in industrial applications such as cutting, welding, spraying, metallurgy, materials processing, chemical engineering, and waste treatment. Numerical simulation of arc‑heated plasma helps to deepen our understanding of the physical processes involved and to optimize the design of plasma generators.

　　Three conclusions can be drawn from the experiment:

　　(1) In studying rotating airflow, it was found that increasing the swirl intensity raises the pressure within the arc chamber and alters its pressure distribution, thereby constricting the electric arc. The swirling gas has only a minor effect on the temperature inside the nozzle orifice and in the jet region, but it imparts higher velocities and stronger shock waves to the plasma outside the nozzle. Moreover, by redirecting the flow near the cathode and elevating the local pressure, the swirling gas accelerates cathode erosion. (2) Parameter studies revealed that lengthening the nozzle orifice increases the jet’s maximum velocity, elevates the arc‑chamber pressure, and expands the radius of the high‑velocity jet region downstream of the shock wave. Reducing the orifice radius, in turn, raises the arc‑chamber pressure, intensifies the shock wave, and shifts the radial peak values of jet velocity and energy flux away from the axis. These effects facilitate enhanced energy and momentum exchange between the arc and the workpiece, thereby increasing cutting speed. Gas flow rate influences both the velocity and temperature profiles of the plasma; strong gas flow, owing to its pronounced cooling effect, contracts the arc, raises the arc voltage and power, and consequently boosts jet velocity, temperature, and energy flux. Arc current exerts a highly significant impact on both the velocity and temperature fields of the plasma, with the energy flux in the plasma jet being nearly proportional to the arc current. (3) By comparing the plasma flow fields generated by two distinct torch designs, it was observed that shielding gas has little influence on the plasma’s temperature and velocity distributions. A vertically directed shielding gas stream creates an obstructive barrier at the torch nozzle, leading to a modest increase in internal pressure, though the overall change remains small. The protective effect of shielding gas is confined primarily to the shock‑wave region immediately outside the nozzle; introducing shielding gas attenuates the shock‑wave intensity. Compared with the no‑shielding condition, shielding gas enhances cooling, resulting in a slight rise in arc voltage. When the composition of the shielding gas is varied, it was found that the oxygen content in the arc column remains unaffected, meaning that changes in shielding‑gas makeup do not alter arc voltage. Calculations indicate minimal mixing of oxygen with ambient gases along the axis; even 10 mm downstream of the nozzle, the mole fraction of oxygen still exceeds 90%.

　　This paper presents the basic definition of an arc plasma torch and several conclusions drawn from experimental results.