Proposal of new criterion for splashing of thermal sprayed particle onto flat substrate surface

摘要

In a collision of a liquid droplet onto a flat surface, Splashing parameter: K=We{sup}0.5Re{sup}0.25 has been used to evaluate the flattening behavior and a critical value of K: K{sup}c was introduced as a criterion for the splashing. In order to evaluate K of thermal sprayed particle, in-flight measurement for the velocity and temperature of the particle was conducted in this study. As a flattening pattern of the thermal sprayed particle changed significantly with a substrate temperature, Transition temperature: T{sub}t was also measured by changing the substrate temperature. Both K and T{sub}t showed a tendency of monotonous decreasing with increasing the spray distance and a strong linearity was recognized in a K-T{sub}t relationship. This straight line corresponds to a critical value for the splashing. However, as an influence of substrate temperature on the flattening is essentially independent of K a new criterion for the splashing in the flattening of the particle was proposed in the study. That is, Splashing parameter on flattening: K{sub}f=0.5a{sup}1.25 Re{sup}(-0.3) K was proposed, where a is defined as a ratio of the flattening velocity to the impact velocity of the particle, and the critical K{sub}f: K{sub}f{sup}c corresponds to a net critical condition for the splashing. Consequenfly, by introducing the measurement results from a freely falling experiment, K{sub}f{sup}c was estimated to be about 6.