Dc Arc Torch Research Articles

Diagnostics of Plasma Jet Generated in Water/Argon DC Arc Torch

Thermal plasma jet generated by the torch with water/argon stabilized arc was investigated. Plasma torches of this type have been used for plasma spraying, waste treatment and gasification of organic materials. Electric probes, enthalpy probe, and schlieren photography were used for diagnostics of the jet in the region downstream of the torch exit. Information about structure and shape of plasma jet was evaluated from the measured data. Large extent of radial plasma spread and high level of turbulence were found from both the schlieren and the probe diagnostics. Plasma temperature corresponding to measured ion saturation currents was determined using calculated composition of plasma assuming ex-istence of local thermodynamic equilibrium.

Theoretical and experimental investigations of the coupling of time-dependent parameters in a blown arc plasma torch

A low-power dc arc torch using nitrogen as plasma-forming gas is studied to highlight the modulation of plasma jet specific enthalpy and speed at the nozzle exit. A special design is used for the torch and by tuning the arc current and the mass flow rate a resonant oscillating mode is obtained in the kHz range, for which the arc voltage presents a periodic triangular waveform, which is the result of the combination of the input parameters. At stabilized current and following the voltage, the electric power is modulated for the specific enthalpy, the mass density and the speed of the plasma at the nozzle exit. A change in the plasma speed is accompanied by a change in the momentum of the jet, which must influence the pressure inside the torch and particularly in the cathode cavity, the volume of which stores the cold gas before it enters the arc region. Even though the torch is fed with a constant flow rate, the arc is subjected to a more or less fluctuating flow rate depending on the cathode cavity volume. The link between the fluctuating components of the different parameters is searched by using a conservation equation and solutions are obtained by means of Fourier analysis. The results obtained are consistent with speed measurements and time-resolved temperature measurements.

Effects of Anode Nozzle Geometry on Ambient Air Entrainment Into Thermal Plasma Jets Generated by Nontransferred Plasma Torch

Summary form only given, as follows. In plasma spraying, higher temperature and velocity of thermal plasma jets are preferable for producing high qualities of protective coatings for their industrial uses, because the sprayed coating powders are melted and accelerated in the plasma flame ejected from a non-transferred DC arc torch through an ambient air toward a substrate. In the typical plasma spray process operated under an atmospheric-pressure condition, the entrainment, of ambient air into the thermal plasma jet is inevitable. An air inflow to the flame alters chemical compositions of the plasma species, cools the thermal plasma flame, and decreases the jet velocity. Furthermore, the dissociation of entrained air enhances the specific heat of plasma, and then the plasma temperatures decrease even when operation power level of the plasma torch is not changed. Consequently, the gradients of temperature and velocity in the plasma jet increase with the degree of air entrainment. Therefore, the ambient air entrainment should be controlled to the lower degree for getting the better quality of coating products with higher purity, density and bond strength. In this experimental work, the geometrical effects of anode nozzle of the non-transferred plasma torch on the air entrainment are examined by measurements using a quadruple mass spectrometer. Two different types of anode nozzle, i.e., tubular and stepped nozzles are employed for the torch. For each nozzle, air contents in the thermal plasma are measured to find the effects of nozzle geometry on the ambient air mixing with the plasma species. The radial and axial distributions of plasma temperature and velocity are also measured. By analyzing the measured results of the thermal plasma characteristics and the geometrical effects of nozzle shape on the air entrainment, the suitable design requirements of the nozzle are determined for optimal processes of plasma spraying.

Effect of Anode Attachment on Flow Structure in Plasma Jet Generated in DC Arc Torcha

ABSTRACT: Effect of an arc anode attachment on stability of plasma jet was studied in a plasma torch with dc electric arc stabilized by water. The torch was equipped with an external anode and thus direct observation of interaction of the anode attachment with the plasma jet was possible. High speed photography of the anode region and the jet was synchronized with voltage measurements. Different modes of the anode attachment were distinguished and movement of the attachment along the anode surface was photographed. Formation of an anode jet was observed. An interaction of the anode jet with the main jet produce strong instability of plasma flow in the jet which rapidly develops into jet whipping and fluttering. It is shown that momentum flux in the anode jet is comparable with the one in the main jet and thus a formation of the anode jet is principal cause of a plasma jet instability. Results of spectroscopic diagnostics of the anode region indicate strong entrainment of ambient air into the anode jet.

Modeling Turbulence in a Thermal Plasma Reactor

ABSTRACTNumerical models describing the plasma physics in the column and plume of a nontransferred, dc arc torch were used in conjunction with two experiments to quantify the extent of turbulence in the free plume. Numerical predictions were made by solving the governing conservation equations with suitable boundary conditions. The solutions indicate a high temperature, high velocity region starting at the anode which decays rapidly as the plume interacts with the atmosphere. The turbulent viscosity is predicted to be up to 140 times higher than the molecular viscosity at specific locations. Modeling results for the plume compare favorably with spectroscopic temperature measurements, and with the cone angles measured with holographic interferometry, which quantifies the amount of turbulence in the plume.

Qualitative Analysis by Photoacoustic Spectroscopy of Amorphous Uranium Tetrafluoride Deposits

Abstract Recent studies concerning uranium plasma chemistry have confirmed the generally complicated nature of uranium chemistry1. Uranium plasma, generated by either rf-heating or dc arc torch argon heating of uranium hexafluoride, tends to react with its environment to produce among other compounds both fluorides and oxy-fluorides. The products are characterized as amorphous, powdery deposits. While uranyl fluoride can be identified readily by its infra-red absorption band, uranium tetrafluoride is not easily analyzed by any routine, non-destructive technique. Procedures such as Ion Scattering Spectroscopy and Secondary Ion Mass Spectrometry are expensive and time consuming; while, X- ray and electron deffraction can not overcome the amorphous nature of the plasma deposits.