Deformation behavior of a liquid droplet impinging on hot metallic surfaces above the Leidenfrost temperature

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The deformation process of a droplet impacting a hot surface has been investigated by many double exposure photographs on the basis of statistical procedure. When a droplet impacts a hot surface with low Weber numbers, the droplet spreads on the surface, reaches a maximum diameter, recoils and finally rebounds from the surface. For larger Weber numbers, we have found that the droplet breaks up into small parts in the recoiling process. Wiht increasing the Weber number further, the droplet shatters in the spreading process. Also, we have investigated the effect of kind of surface material on the droplet deformation process. The effect of kind of surface material has been hardly recognized in the range of low Weber numbers such that the droplet rebounds from the surface without disintegration. However, it has been found that the critical Weber number whether or not the droplet break up into small parts during the deformation is changeable depending upon the kind of surface material.The deformation behavior of droplet has been analyzed numerically. The system of governing equation is the Navier-Stokes equations for the incompressible viscous fluid flow in the axisymmetric system. The effects of viscosity, gravity and surface tension have been taken into account. The system of governing equations has been solved by the finite differencing method. The deformation process of droplet impinging on a cold surface at room temperature as well as a hot surface above the Leidenfrost temperature has been analyzed. The numerical results have been compared with the experimental data to verify the validation of mathematical model. As a result, the numerical results have been found to agree well with the experimental data. Also, it has been clarified theoretically that the droplet rebounding occurs owing to the effect of surface tension.