Experimental investigation of Leidenfrost vapor film formation, stability and lifetime on ZnO-based superhydrophobic copper surfaces

In this work, the formation, stability and lifetime of the Leidenfrost vapor film on differently modified copper surfaces are experimentally investigated and the effect of these properties on the reduction of hydrodynamic resistance is examined. The Leidenfrost phenomenon, which manifests itself in the formation of a stable vapor film between a heated surface and a liquid, changes the heat transfer processes and the interaction of the liquid with a solid surface, and therefore, its effect can be applied to reduce hydrodynamic friction. Four types of copper surfaces were prepared for the study: polished Cu, Cu-FeCl 3 , Cu + ZnO PMHS and Cu-FeCl 3 + ZnO PMHS . Their morphology and crystalline phase composition were evaluated using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Surface modification significantly affects the formation of the Leidenfrost vapor film, its stability and lifetime. Experiments were performed with 19 mm diameter pure copper spheres in 20 °C water. It was found that a clearly visible and stable vapor film is formed in water when the copper surface temperature reaches at least 160 °C. Experiments with free falling samples reveal that different treatments of copper surfaces, along with varying heating boundary conditions, significantly affect the formation of vapor-layer around samples, leading to substantial reductions in drag coefficients. Study gives a valuable insight into the interplay between vapor layer thickness, specimen velocity, and potential applications in fluid dynamics.