Meng Xian

Arc Root Attachment on the Anode Surface of Arc Plasma Torch Observed with a Novel Method

The arc-root attachment on the anode surface of a dc non-transferred arc plasma torch has been successfully observed using a novel approach. A specially designed copper mirror with a boron nitride film coated on its surface central-region is employed to avoid the effect of intensive light emitted from the arc column upon the observation of weakly luminous arc root. It is found that the arc-root attachment is diffusive on the anode surface of the argon plasma torch, while constricted arc roots often occur when hydrogen or nitrogen is added into argon as the plasma-forming gas.

Comparative Observation of Ar, Ar-H2 and Ar-N2 DC Arc Plasma Jets and Their Arc Root Behaviour at Reduced Pressure

Results observed experimentally are presented, about the DC arc plasma jets and their arc-root behaviour generated at reduced gas pressure without or with an applied magnetic field. Pure argon, argon-hydrogen or argon-nitrogen mixture was used as the plasma-forming gas. A specially designed copper mirror was used for a better observation of the arc-root behaviour on the anode surface of the DC non-transferred arc plasma torch. It was found that in the cases without an applied magnetic field, the laminar plasma jets were stable and approximately axisymmetrical. The arc-root attachment on the anode surface was completely diffusive when argon was used as the plasma-forming gas, while the arc-root attachment often became constrictive when hydrogen or nitrogen was added into the argon. As an external magnetic field was applied, the arc root tended to rotate along the anode surface of the non-transferred arc plasma torch.

Arc Voltage Fluctuation in DC Laminar and Turbulent Plasma Jets Generation

Arc voltage fluctuations in a direct current (DC) non-transferred arc plasma generator are experimentally studied, in generating a jet in the laminar, transitional and turbulent regimes. The study is with a view toward elucidating the mechanism of the fluctuations and their relationship with the generating parameters, arc root movement and flow regimes. Results indicate that the existence of a 300 Hz alternating current (AC) component in the power supply ripples does not cause the transition of the laminar plasma jet into a turbulent state. There exists a high frequency fluctuation at 4 kHz in the turbulent jet regime. It may be related to the rapid movement of the anode attachment point of the arc.

Heat Flux Characterization of DC Laminar-plasma Jets Impinging on a Flat Plate at Atmospheric Pressure

By using steady and transient methods, the total heat fluxes and the distributions of the heat flux were measured experimentally for an argon DC laminar plasma jet impinging normally on a flat plate at atmospheric pressure. Results show that the total heat fluxes measured with a steady method are a little bit higher than those with a transient method. Numerical simulation work was executed to compare with the experimental results.

Heat Transfer from a dc Laminar Plasma-Jet Flow to Different Solid Surfaces

The heat flux distributions were measured by using transient method for an argon dc laminar plasma-jet flow impinging normally on a plate surface embedded with copper probes. Different powders were coated on the probe surfaces and the effect of powder coatings on the heat transfer from jet flow to the probe surface was examined. Experimental results show that the maximum values of the heat flux to the probe increase with the coating of fine metal powders, while for the surfaces coated with fine ceramic powders, the maximum values of heat flux decrease, compared with that to the bare copper probe surface.