Novel method for in-flight particle temperature and velocity measurements in plasma spraying using a single CCD camera

Abstract

A novel, technically simple imaging system for individual, in-flight particle temperature and velocity measurements for plasma and other thermal spray processes is described. A custom double dichroic mirror is used to add spectral resolving capability to a single, black-and-white, fast-shutter digital charge coupled device (CCD) camera. The spectral double images produced by the individual in-flight particles are processed using specialized image processing algorithms. Particle temperature determination is based on two-color pyrometry, and particle velocities are measured from the length of the particle traces during known exposure times. In this paper, experimental results using the first prototype system are presented. Laboratory tests were performed using rotating pinholes to simulate in-flight particles, and plasma spraying experiments were performed with commercial, standard spraying equipment operated with Al₂O₃ and NiCrAlY powders. The prototype instrument can be readily used to determine velocity and temperature distributions of individual in-flight particles from the imaged region of interest of the plume. Dividing the imaged area into smaller sections, spatial distributions of particle temperature, velocity, and number of detected particles can be studied. The study aims to develop a technically simple, single imaging instrument, which can provide a visual overview of the spray plume in combination with quantitative evaluation of the most important spray particle parameters.