Thermal Antibubbles: When Thermalization of Encapsulated Leidenfrost Drops Matters

Antibubbles are ephemeral objects composed of a liquid drop encapsulated by a thin gas shell immersed in a liquid medium. When the drop is made of a volatile liquid and the medium is superheated, the gas shell inflates at a rate governed by the evaporation flux from the drop. This thermal process represents an alternate strategy for delaying the antibubble collapse. We model the dynamics of such “thermal” antibubbles by incorporating to the film drainage equation the heat-transfer-limited evaporation of the drop, which nourishes the gas shell with vapor, as for Leidenfrost drops. We demonstrate that the inflation of the gas shell is drastically inhibited by the thermalization of the initially colder drop. Because of this thermalization effect, smaller drops evaporate much faster than larger ones.

Figure 1

Thermal antibubble: the heat provided by the hot bath is used for both evaporating and thermalizing the initially cold drop. The generated vapor, while draining from bottom to top, delays the antibubble collapse.

Figure 2

Snapshot series every 24 ms presenting the motion of a thermal antibubble made of an HFE-7100 droplet released into a bath of V20 silicone oil heated at $T_b=120°\mathrm{C}$. The change of direction occurs 203 ms after the first image, i.e. between the ninth and the tenth snapshots. Inset: snapshot series presenting the formation of the thermal antibubble in the same conditions. A satellite thermal antibubble is seen to be formed within the “tail” of the main one. The scale bar applies to all snapshots.

Figure 3

Normalized thermal antibubble volume as a function of time for different $\mathrm{\Delta }T$. Thick dashed lines represent the model output, adjusted to the particular experiment represented with filled circles. The thin crosses correspond to additional experiments. Thick dotted lines are the model output without the thermalization term ($\mathrm{\Lambda }=0$). Inset: all of the non-normalized experimental data for $\mathrm{\Delta }T=59$ and 79 K.

Figure 4

Evolution of the thermal antibubble volume computed for $\mathrm{\Delta }T=79\mathrm{K}$, $k_v=14.4\mathrm{mW}/\mathrm{m}/\mathrm{K}$, and varying initial radius. Symbols are experimental results for two different radii.