MONITORING THE IMPACT OF LIQUID ALUMINA PARTICLES UNDER PLASMA CONDITIONS USING AN IMAGING TECHNIQUE

Our work aims to study in an experimental way, including imaging, the impact of alumina droplets plasma sprayed onto dry surfaces. This study is achieved by using a complex experimental set-up including :
• A controlled atmosphere chamber allowing to study different types of substrate materials. In this chamber is set a plasma torch devoted to the alumina liquid droplets generation.
• An in-flight droplet characterization device including a PDA (droplet velocity and size measurement) and a fast (100ns) two-color pyrometer. A monochromatic pyrometer is also used in order to check the substrate surface temperature.
• An imaging device is used to observe the droplet impact. It includes a fast numerical camera equipped with a long distance microscope.
The first results obtained with all;lmina particles are in agreement with the Sommerfeld rules that predict the droplet behavior (rebound, deposition, splashing) : splashing occurs for high values of the Sommerfeld parameter K, deposition of the droplet occurs for low values of K. Yet, unexpected phenomena such as splashing at low K are also observed and explained by the important surface roughness and the low surface temperature.