Relation Between the Arc-Root Fluctuations, the Cold Boundary Layer Thickness and the Particle Thermal Treatment

Abstract

International audienceIn plasma spraying, the arc-root fluctuations, modifying the length and characteristics of the plasma jet, have an important influence on particle thermal treatment. These voltage fluctuations are strongly linked to the thickness of the cold boundary layer (CBL), surrounding the arc column. This thickness depends on the plasma spray parameters (composition and plasma forming gas mass flow rate, arc current, etc.) and the plasma torch design (anode-nozzle internal diameter and shape, etc.). In order to determine the influence of these different spray parameters on the CBL properties and voltage fluctuations, experiments were performed with two different plasma torches from Sulzer Metco. The first one is a PTF4 torch with a cylindrical anode-nozzle, working with Ar-H2 plasma gas mixtures and the second one is a 3MB torch with either a conical or a cylindrical anode-nozzle, working with N2-H2 plasma gas mixtures. Moreover, arc voltage fluctuations influence on particle thermal treatment was studied through the measurements of transient temperature and velocity of particles, issued from an yttria partially stabilized zirconia powder with a size distribution between 5 and 25 lm

Nitrogen Fixation by an Arc Plasma at Elevated Pressure to Increase the Energy Efficiency and Production Rate of NOx

“…The increased pressure leads to a higher temperature in the reactor (see the Mechanistic Considerations section below), which in turn reduces the size of the cold gas boundary layer and its effect on the attachment point. The drag force resulting from the gas flow can no longer extend the arc to a point in which restrike can occur, and the more stable takeover mode is achieved . Furthermore, the reduced velocity results in a reduced swirl intensity and the arc experiences reduced contracting force.…”

“…The drag force resulting from the gas flow can no longer extend the arc to a point in which restrike can occur, and the more stable takeover mode is achieved. 32 Furthermore, the reduced velocity results in a reduced swirl intensity and the arc experiences reduced contracting force. This leads to thickening of the arc column and contributes to a more stabilized arc.…”

Advancement of Powder Spheroidization Process Using a Small Power DC-RF Hybrid Plasma Flow System by Sinusoidal Gas Injection

“…3 (b). The periodical DC arc voltage fluctuation indicates the variation of electrical resistance of DC plasma jet caused by arc root fluctuation (10), (11) .…”

Electrode Phenomena in Plasma Sources

“…When operating with pure Ar or Ar/He mixtures in the takeover mode, addition of hydrogen or nitrogen beyond a certain amount constricts the arc and increases the boundary layer thickness with a shift to restrike-like behavior. Increasing the arc current reduces the anode boundary layer thickness and the arc root fluctuations, but the effect of increasing the total mass flow rate and the fraction of the secondary gas hydrogen can be different for different nozzle designs and different if the primary gas is argon or nitrogen (Nogues et al 2007). For the steady mode, only minimal fluctuations are observed, but unfortunately the lifetime of the anode is very limited.…”