|
2229 |
|
Monday, May 03, 2010, Hullet Room 3:00 PM Process Diagnostics 1 |
|
Shadow imaging of liquid precursors under plasma spraying conditions |
|
Armelle Vardelle* / University of Limoges-CNRS, France Michel Vardelle / University Of limoges , France Simon Goutier/ University of Limoges, France Christophe Chazelas/ University of Limoges, France |
|
The use of precursors in plasma spraying in the form of a liquid suspension or solution has extended the potential of thermal spraying for producing nanostructured coatings with a large range of architectures and, also, complex functional coatings. However, the performance of such applications depends on the ability to produce and maintain a stable spray pattern with consistent droplet/particle trajectories so as to (i) form a coating with a specific microstructure and (ii) maximize the deposition efficiency. Both depend on the injection of the liquid feedstock into the gas flow and the behaviour of the droplets in the core and periphery of the plasma jet cone. Up to now, there have been few reports in the literature on experimental observations of the interactions between the injected liquid and the plasma jet, although they are essential in understanding the mechanisms that control these processes and, also, for validating the numerical simulation of the liquid precursor spray process. This paper presents a shadow imaging technique that has been adapted to the visualization of liquid injected in the plasma jet in the form of a liquid stream or drops. This technique is well-established for visualization of compressible flow fields and is based on pulsed back light illumination of the liquid material using a double pulsed laser and CCD cameras. The experimental system developed provides a global visualization of the liquid injection and also tracks the drop behaviour by means of a zoomed view of the plasma core, thus making it possible to measure the droplets position, number, size and velocity. |