STUDY ON THE MEASUREMENT OF THE DIAMETERS AND THEIR IMPACT DYNAMICS PARAMETERS FOR THE PARTICLES USING HIGH-SPEED PHOTOGRAPHY

The presence of fouling and slagging on the boiler heat transfer surface is a significant factor affecting the safe and economical operation of the boiler. In order to address these issues, it is imperative to investigate the impact dynamics of particles and to comprehend the mechanisms of particle adhesion and rebound. In this study, a dynamic test platform for single-particle impact on walls under high-temperature conditions was constructed to study the impact dynamics of micrometer-scale particles on walls by using particle shadow velocimetry (PSV) technology. Meanwhile, a MATLAB-based particle image processing program, utilizing sub-pixel interpolation in conjunction with the maximum inscribed circle method, has been proposed as a reliable measurement technique. This approach has been empirically validated, addressing the challenges associated with accurately measuring the diameter of spherical particles in high-speed photography. Based on this method, the measurement accuracy of the particle impact dynamics parameters has been significantly enhanced. Additionally, the study further revealed that, under these experimental conditions, the Otsu threshold segmentation algorithm exhibited superior performance in measuring particle diameters. Additionally, it was observed that both the sub-pixel interpolation method and the interpolation multiplier significantly influenced the measurement outcomes, with a notable window effect being detected. The normal restitution coefficient of particles demonstrated a decreasing trend with increasing impact velocity, and the decreasing trend of particle velocity during impact and rebound indicated that the flow field effect had a certain influence on the particle dynamics characteristics, which also needs to be further considered in the measurement results. As the normal restitution coefficient of the particles increased, the rebound angle generally tended to decrease gradually. These findings not only deepen our understanding of the impact dynamics of single particles but also provide a solid foundation for the study of complex multi-particle systems. They hold significant importance for the establishment and analysis of discrete element models in the impact processes of particulate materials.