Comparative study of the structure of gas-stabilized and water-stabilized plasma jets

The near-field structures of a gas- stabilized plasma jet and a water-stabilized plasma jet were investigated using a nano-pulsed laser probe and stroboscopic focusing schlieren techniques. The high exit temof the gas caused laminar flow conditions at the exit of the jet, producing instability waves in the region. Significant heat conduction to the ambient fluid and volumetric expansion of the ambient gases in the near- field were observed in the schlieren images of these jets. Considerable asymmetry in the mixing and entrainment region of the water- stabilized plasma jet was also visible, whereas no significant asymmetry occurred in the luminous core of the jet. The particles injected into the plasma jet, which were visualized by the pulsed- laser technique, were confined to a narrow central core of the jet in the near- field of the jet. The combination of the two visualization techniques used in the present study allowed nonintrusive monitoring of the plasma spray process in an effort to enhance the quality of the processed deposits.