When the liquid film can dries out, the wall temperature spikes (in this video, a thin coating on the inner surface of the glass is heated). Disturbance waves can sometimes re-wet the wall (intermittent dryout).
In additional to bubble nucleation, vapor bubbles can be entrained in thick film annular flows through droplet impact.
In thicker annular films, two dryout regions can form in the wake behind an obstruction. For more information, see Joe’s thesis.
At lower qualities, there are typically many more vapor bubbles entrained in the liquid film, especially in disturbance waves. Bubble nucleation is also possible in this flow. We observed nucleation under disturbance waves at higher heat fluxes.
Bubble nucleation is sometimes at the edges of the wake that forms behind obstructions.
Zoomed in image showing the upstream dry region more clearly.