Measurement of plasma and particle velocities in a thermal plasma jet by correlation and PIV methods

Summary form only given. Distribution of particle velocities is an important parameter affecting the quality of coatings in plasma spraying technologies. In studies of the interaction between injected particles and plasma flow the knowledge of plasma velocity and temperature plays a decisive role. Particle velocities in the plasma jet area are mostly measured using laser methodologies, such as laser strobe, LDA and PDA methods. A recent PIV (particle image velocimetry) method used mainly in measurements of velocity distributions in "cold" flows seems to be a very perspective technique offering the advantage of a measurement range including the whole area of interest. Gas velocities in thermal plasma jets may be evaluated from light fluctuations carried by the flow. In our experimental arrangement we have injected the corundum particles with sizes 25-32 mum transversally into the plasma jet generated by a dc argon plasma torch. The plasma jet optical radiation was recorded by a system of 2 fast shutter CCD cameras equipped with a rotating mirror that provided series of 5 plasma jet images from perpendicular directions with exposure times 300 ns and intervals 10 mus. The plasma velocities were evaluated from the correlations of fluctuations in reconstructed 3D distributions of the plasma jet optical radiation. Particle velocities were measured by the PIV method using Nd-YAG laser emitting at 532 nm. The laser light reflected by the particles was filtered by an interference filter with the half-width 1 nm in order to eliminate the plasma jet optical radiation. Due to filtering it was possible to do PIV measurements also in the strongly radiating parts of the plasma jet. The results have shown that the combination of correlation/PIV methods is suitable for further investigations of plasma jet/particle interactions.