This work was devoted to the study of the @namic and static behavior of adc vortex plasma torch with a well-type cathode (power level below lOO kW). The dynamic behavior of the torch was characterized by the fluctuations of arc voltage and current, plasma jet radiation, and acoustic pressure. Characteristic frequencies of the arc root movement inside the torch were observed. By numerical simulation (with the numerical code MELODIE), it was shown that the position of the erosion area at the wall of the well-type cathode was linked to the variation (vs. its diameter) of the axial velocity along the cathode channel near the wall. The static behavior of the torch was investigated for different cathode designs. The variations of voltage U with arc current I, gas flow rate G, nature of the gas, and cathode design were represented by semiempirical relationships established between dimensionless numbers. By dimensional analysis, the behavior of this torch was compared with that of two powerful tarches: the Aerospatiale and the Plasma Energy Corporation torches. NOMENCLATURE d, outflow nozzle diameter (m) d., anode diameter (m) de, cathode diameter (m) D, vortex chamber diameter (m) f, frequency (Hz) G, mass flow rate of plasma gas (kg/s) IEquipe "Plasmas-Lasers-Matrriaux," Laboratoire "Mat&iaux C&amiques et Traitements de Surfaces," URA320 CNRS, 123, Av. A. Thomas, 87060 Limoges Cbdex, France. 2Electricite de France, Direction des Etudes et Reeherches, Drpartement ADEI, Les Renardirres, BP !, 77250 Motet Sur Loing, France. 257 0272-4324/95/0600-0257507.50/0 © 1995 plenum Publishing Corporation 258 Brilhac et al.G', volume flow rate of plasma gas (slm) h0, mass enthalpy (J/kg) Hp, mass enthalpy of plasma gas (MJ/kg) L arc current intensity (A) l,, anode length (m) It, cathode length (m) p, gas pressure (Pa) P, electrical power (W) To, reference temperature corresponding to the plasma gas (K) Vu, axial velocity of the plasma gas (m/s) V., azimuthal velocity (m/s) Vu .... maximum axial velocity (m/s) Vo.,,., minimum axial velocity (m/s) or0, electrical conductivity (A 2 s3/kg m 3) /.to, viscosity (kg/m s) r/, thermal efficiency of the torch It0, mean thermal conductivity (W/m K) At, time lag (s)
I% electron concentration in
Dimensionless GroupsRe= G/I.tod, Reynolds number Sf=fd2~/l, frequency criteria Sg = (I,,. de~It" d,,), torch design criteria Si = 12/Gdcroho, energy criteria Su = Udcro/L electric field intensity criteria
