The influence of laminar and turbulent flows upon the electrical characteristics of wall-stabilised arcs

Abstract

Measurements are reported of the electrical properties of wall-stabilised arcs subject to an imposed axial flow of nitrogen under steady current conditions. The current was in the range 10-60 A DC and the gas flow rate was 0-0.6 g s-1 with stabilising bore radii of 2.5 mm and 5 mm. The results of the investigation confirm the existence of two axial zones corresponding to a flow entrainment region and a fully developed column region. The electric field strength along the fully developed region increases with mass flow rate as turbulent effects become more pronounced. An analytical arc model, based upon boundary layer approximations and taking account of molecular and turbulent radial diffusion and axial convection, is presented. Results of calculations using this model predict the trends observed experimentally.

On the physical origin of the nozzle characteristic and its connection with the double-arcing phenomenon in a cutting torch

“…Also note that no ion saturation current was found. This behavior is similar to those presented in wall-stabilized arc experiments with 12 or without externally imposed axial gas flow. 13 In order to get some information from the experimentally determined breakdown at the lowest ṁ value, we must mention that this breakdown will likely occur at the exit of the nozzle.…”

“…Current-voltage characteristics corresponding to large-sized plasma walls in high pressure arcs were obtained only for wall-stabilized arcs with or without imposed gas flow. 12,13 As it is well known, there is no comprehensive theory for interpreting the electron branch in highly collisional plasmas, hence only the ion branch is analyzed in this work. The influence of the collisions on the physical structure of the plasma-sheath transition has been considered under the typical assumption of constant ion mean free path.…”

On the Double-Arcing Phenomenon in a Cutting Arc Torch

“…Also note that no ion saturation current was found. This behaviour is similar to those presented in wall-stabilized arc experiments with (Hill & Jones, 1979) or without externally imposed axial gas flow (George & Richards, 1968) …”

“…So the radiative arc loses are a significant fraction of the electrical power input with a strong contribution in the UV range (Shayler & Fang, 1978). Using the NEC model (Naghizadeh-Kashani et al, 2002) for an atmospheric pressure oxygen plasma, and a copper photoemission coefficient Dowell et al, 2006); the maximum photoelectron current from the nozzle surface results ≈ 10 mA. This photoelectron current will not depend on the nozzle voltage, and only could produce a change in the characteristic curves at the vicinities of the nozzle floating voltage value (see Fig.…”

Supersonic Jets with Periodic Structure due to Arc plasma Expansion into a Low pressure ambient

“…The validity of such "arc channel" model for a gas flow arc under similar experimental conditions was proved in Ref. [18] where con- stant electric field along the fully developed region was measured in a nitrogen arc. Our calculations (see Table 3) also give small variations of all gas flow parameters in the present zone.…”