Onset of the microlayer regime

Determine the precise onset criterion for the transition between the microlayer regime, in which a liquid microlayer forms beneath a growing bubble, and the contact-line regime, in which no microlayer is present.

Background

Whether a microlayer forms beneath a growing bubble is a prerequisite for selecting an appropriate numerical closure. In the microlayer regime, the thin film can in principle be resolved as a fluid-dynamic structure or represented through a film-evolution model; in the contact-line regime, evaporation is confined to a sub-continuum-scale region and requires a contact-line closure.

Several transition criteria have been proposed based on bubble expansion and related physical parameters, but they do not provide a universally accepted description. Identifying the onset of microlayer formation is therefore necessary for determining when microlayer models should be activated and for improving predictions of bubble growth and heat-transfer partitioning.