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.