The Statistical Analysis of Droplet Train Splashing After Impinging on a Superheated Surface

An orderly droplet splashing is established when a water droplet train impinges onto a superheated copper surface. The droplets continuously impinge onto the surface with a rate of 40,000 Hz, a diameter of 96 μm or 120 μm, and a velocity of 8.4 m/s or 14.5 m/s. The heat transfers under different wall temperatures are measured, and the corresponding droplet splashing is recorded and analyzed. The effects of wall temperature, droplet Weber number, and surface roughness on the transition of the droplet splashing are investigated. The results suggest that the transferred energy is kept a constant in the transition regime, but a sudden drop of around 25% is observed when it steps into post-transition regime, indicating that the Leidenfrost point is reached. A higher Weber number of droplet train results in a more stable splashing angle and a wider range of splashed droplet diameter. The surface roughness plays no significant role in influencing the splashing angle in the high Weber number case, but the rougher surface elevates the fluctuation of the splashing angle in the low Weber number case. On the rougher surface, the temporary accumulation of the impact droplets is observed, a “huge” secondary droplet can be formed and released. The continuous generation of the huge droplets is observed at a higher wall temperature. Based on the result of droplet tracking of the splashed secondary droplets, the diameter and velocity are correlated.