APPLICATION OF PHASE DOPPLER ANEMOMETRY IN PAINT SPRAYS

Abstract

For the first time, simultaneous measurements of droplet size and velocity in paint sprays using a phase Doppler anemometer are presented. In agreement with the results of Mie calculations of the scattered light field, first-order refracted light could be used successfully for phase Doppler measurements of two different water-based paints, a laquer and a silver metallic paint. Preliminary measurements, including a comparison with results from digital image processing of stroboscopic light pictures of paint droplets, were performed to demonstrate the accuracy and repeatability of the measurements. Furthermore, comparative measurements in original paint spray guns using an optically homogenous water-sucrose-alcohol solution with similar viscosity and surface tension as the specific paints used herein have shown almost identical droplet size distributions. Extended measurements in a spray booth were performed, changing a variety of parameters such as gun type, air cap, and paint and airflow rates. Profiles of mean droplet velocity and droplet size were taken at three different distances, 5, 15, and 30 cm downstream from the nozzle. The results have shown some of the expected dependencies of the local droplet velocity and size distributions on global parameters, e.g., an increase of the mean sizes with decreasing airflow.