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Experimental study on the effect of the liquid/surface thermal properties on droplet impact

Lamini Omar (School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, China)
Wu Rui (School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, China)
Zhao Changying (School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, China), changying.zhao@sjtu.edu.cn

Droplet impact on hot surfaces is widely encountered in industry and engineering applications. In the present paper we investigate the effect of the combination of the droplet liquid type and the solid surface type and their effect on droplet impact dynamics. We test three surfaces, copper 110, aluminum 1199, and stainless steel 304, and two liquids, water and ethanol. These surfaces and liquids are characterized by high and low thermophysical properties. The three surfaces are tested with water to investigate the effect of the surface on the droplet dynamics. After that, we test both liquids with aluminum. Our findings showed that the Leidenfrost temperature does not always correlate with the surface thermal proper-ties as reported in the literature. Some surfaces can undergo changes because of the heating and this reduces their initial thermal properties. For this reason, such surfaces are capable to show two Leidenfrost temperatures because of the thermophysical properties reduction during heating. Our findings also revealed that the Leidenfrost temperature of liquids with low thermophysical properties including surface tension, evaporation latent heat and density show trivial effect by the droplet impact velocity; i.e. the Leidenfrost temperature show trivial increase by increasing the droplet impact velocity. Liquids with high thermophysical proper-ties show significant Leidenfrost temperature increase by increasing the impacting velocity.

Keywords: Droplet impact, Leidenfrost temperature, Thermophysical properties, Phase diagram, Surface Oxidation.