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~(0.5)Re~(0.25) has been used to evaluate the flattening behavior and a critical value of K: K~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_t was also measured by changing the substrate temperature. Both K and T_t showed a tendency of monotonous decreasing with increasing the spray distance and a strong linearity was recognized in a K-T_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_f =0.5a~(1.25)Re~(-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_f: K_f~c corresponds to a net critical condition for the splashing. Consequently, by introducing the measurement results from a freely falling experiment, K_f~c was estimated to be about 6.