Tue June 9th 2015
16:00 – 17:00
HT 900
Master defense Interferometric measurement of surface cooling by Leidenfrost drops
Martin Klein Schaarsberg

Details:

When a liquid drop is placed on a highly superheated surface, it can be levitated by its own vapor. This remarkable phenomenon is referred to as the Leidenfrost effect. The isolating vapor film results in a severe reduction of the heat transfer rate compared to boiling at lower surface temperatures, where the drop stays in contact with the surface. A commonly made assumption is that the surface is isothermal, which is questionable for poorly thermally conducting materials. Here we develop a technique based on Mach-Zehnder interferometry to investigate the surface cooling effect. The 3D substrate temperature field is reconstructed from interferometric data by a novel Abel inversion method that imposes the reconstructed field to satisfy the steady heat equation. This way we are able to measure a local cooling on the order of 75 °C for ethanol Leidenfrost drops on a quartz surface initially at 300 °C. From the temperature field, we obtain the local heat flux inside the substrate and use it to estimate the vapor film thickness profile. The heat transfer rate through the vapor film is compared to the heat transfer rate measured by the evaporation rate. This work provides a new tool to improve the understanding of the Leidenfrost effect.
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