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Dynamics of Vapor Layer Under a Leidenfrost Drop

In the Leidenfrost effect a small drop of fluid is levitated above a sufficiently hot surface, on a persistent vapor layer generated by evaporation from the drop. The vapor layer thermally insulates the drop from the surface leading to extraordinarily long drop lifetimes. The top-view shape of the levitated drops can exhibit persistent star-like vibrations. I extend recent work [Burton et al. PRL 2012] to study the bottom surface of the drop using interference-imaging. In this work I use a high-speed camera and automated image analysis to image, locate and classify the interference fringes. From the interference fringes I reconstruct the shape and height profile of the rim where the drop is closest to the surface. I measure the drop-size dependence of the planar vibrational mode frequencies, which agree well with previous work. I observe a distinct breathing mode in the average radius of the drop, the frequency of which scales differently with drop size than the other modes. This breathing mode can be tightly coupled to a vertical motion of the drop. I further observe a qualitative difference in the structure and dynamics of the vertical profile of the rim between large and small drops.