Effect of Arc-anode Attachment on Thermal Plasma Jet
An interaction of plasma flow with an arc-anode attachment in a dc arc plasma torch was investigated. Statistical processing of the photographic images of plasma jet was used for analysis of an effect of the anode attachment on structure and stability of plasma flow. Deflection, flattening and flutter of the plasma jet was found to be caused by disturbing effect of the arc-anode attachment.
Experimental investigation of development of fully turbulent plasma jet generated by hybrid gas-water torch
Thermal plasma jets are characterized by strong interaction with surrounding atmosphere. Such jets in most cases represent fully turbulent flow. Fast transition of the plasma jet generated by the hybrid gas-water torch to turbulent behavior is caused by a strong difference between ambient air density and density of the plasma, which is extremely low due to high jet temperature. Development of the plasma jet characteristics and mixing of the jet fluid with ambient air along the jet were experimentally studied. Several diagnostics methods were applied to enable obtaining the properties of the whole jet. The work considers processes in the plasma jet depending on generation conditions. Arc current and flow rate of the plasma forming gas, which determine properties of the arc and correspondingly of the plasma jet, were varied. The obtained data were applied to analyze heat, mass and momentum transfer in the gas-water jets.
Characterization of d.c. plasma torch voltage fluctuations
The arc root fluctuations at the anode-nozzle of a d.c. plasma spray torch with a special configuration of the electrodes allowing to work with the same gas flowrate with nozzle diameters ranging from 6 to 10 mm were systematically studied. The plasma gas was Ar/H2 (25 vol % H2), the current was varied between 200 and 600 A and the plasma gas flowrate between 24 and 80 slm. After 30–60 mn working the nozzle wall started to be sufficiently eroded to have a stagnant arc spot which lived until arcing created another one. It was shown that the life time of the upstream arc spots were 30–40 % longer than the downstream ones which could play an important role in the electrode erosion. Dimensional analysis allowed to find a relationship between the nozzle diameter D, the arc current I and gas flow rate G and the mean spot lifetime which is closely connected with the difference between D and the electrical diameter of the arc column. The comparison of voltage signal and light emission at a point of the plasma jet close to the nozzle exit on its axis allowed to determine the mean electrical field within the plasma column and the mean position of the arc root. The comparison with the electrode erosion area for well defined conditions showed a good correlation with the calculated arc root position.