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Progress in Plasma Processing of Materials, 2003

ISBN:
978-1-56700-192-1 (Print)
978-1-56700-447-2 (Online)

DETERMINATION OF FLOW VELOCITY FROM ANALYSIS OF HYDRODYNAMIC OSCILLATIONS OF THERMAL PLASMA JET

Vladimir Kopecky
Thermal Plasma Department, Institute of Plasma Physics AS CR, Za Slovankou 3, 18200, Praha 8, Czech Republic

Milan Hrabovsky
Institute of Plasma Physics, Academy of Sciences Za Slovankou 3, 182 00, Prague

Abstract

The coherent oscillations with frequency in the range 20 to 100 kHz are initiated close to the nozzle exit in plasma jet generated by torch with external anode. Frequency and phase velocity of the oscillations were determined experimentally for various diameters of exit nozzle and various plasma compositions. The plasma flow velocity was evaluated from the speed of propagation of shock waves that were initiated by anode breakdowns in a restrike mode of anode attachment. The relation between characteristics of hydro dynamic oscillations and plasma flow velocity were expressed by simple formulae for various flow rates and diameters of exit nozzle. Measured characteristics of the oscillations were than used for determination of plasma velocity. The fluctuations of flow velocity due to ripple of rectified current were determined by this method.