Microlayer dynamics at bubble growth in boiling
Résumé
We investigate experimentally and theoretically the microscale physical phenomena occurring during the growth of a single bubble attached to the heater in nucleate boiling. The experiment is performed with water under normal conditions by using stateof- the-art high-speed (4000 fps) and microscopic scale measurements. The boiling surface consists of an indium-tin oxide (ITO) film deposited on the transparent MgF$_2$ porthole. The ITO heating is performed locally with an infrared (IR) laser directed from below. We study the liquid microlayer that can form between the heater and the bubble. The microlayer profile and macroscopic bubble shape are measured by white light interferometry (WLI) and sidewise shadowgraphy, respectively. The heater temperature is given by an IR camera. We have detected a new feature in the microlayer shape: a bump in the microlayer profile that appears at the initial stage of the bubble growth. A theory that allows us to explain such a profile is presented. We also present a 2D numerical simulation of microlayer dynamics that shows both the bump and the dewetting ridge evidenced in earlier numerical simulations. The bump in the microlayer observed in the experiments does not correspond to the dewetting ridge.
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