Abstract
The Leidenfrost layer is characterized by an insulating vapor film between a heated surface and an ambient liquid. The collapse of this film has been canonically theorized to occur from an interfacial instability between the liquid and vapor phases. The interfacial instability alone, however, is insufficient to explain the known influence of the surface on the film collapse process. In this work, we provide visual evidence for two key mechanisms governing the film collapse: the interfacial instability, and the nucleation of vapor upon multiple non-terminal liquid-solid contacts. These results were obtained by implementing high-speed X-ray imaging of the film collapse on a heated sphere submerged in liquid-water. The X-ray images were synchronized with a second high-speed visible light camera and two thermocouples to provide insight into the film formation and film collapse processes. Lastly, the dynamic film thickness was quantified by analysis of the X-ray images. This helped assess the influence of surface roughness on the disruption of the film. The results of this work encourage further investigation into non-linear stability theory to consolidate the role of the surface on the liquid-vapor interface during the film collapse process.
Highlights
Phase-contrast X-ray images of the liquid-vapor interface were obtained for multiple trials during the experiment
Step 5 Identify the coordinates of the sphere surface and the liquid-vapor interface Step 6 Fit a circle to the coordinates of the sphere surface to obtain the radius rs and center of the sphere measured in pixels
When the film thickness was larger than the field of view, the film thickness was prescribed to be the field of view of the X-ray camera
Summary
The purpose of this study was to provide direct visual data to deduce mechanisms governing the film collapse process
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