Dynamics of a drop floating in vapor of the same fluid

Evaporation of a liquid drop surrounded by either vapor of the same fluid, or vapor and air, is usually attributed to vapor diffusion, which, however, does not apply to the former setting, as pure fluids do not diffuse. The present paper puts forward an additional mechanism, one that applies to both settings. It is shown that disparities between the drop and vapor in terms of their pressure and chemical potential give rise to a flow. Its direction depends on the vapor density and the drop's size. In undersaturated or saturated vapor, all drops evaporate, but in oversaturated (yet thermodynamically stable) vapor, there exists a critical radius: smaller drops evaporate, whereas larger drops act as centers of condensation and grow. The developed model is used to estimate the evaporation time of a drop floating in saturated vapor. It is shown that, if the vapor-to-liquid density ratio is small, so is the evaporative flux; as a result, millimeter-sized water drops at temperatures lower than 70 & DEG; C survive for days. If, however, the temperature is comparable (but not necessarily close) to its critical value, such drops evaporate within minutes. Micron-sized drops, in turn, evaporate within seconds for all temperatures between the triple and critical points. (C) 2022 Author(s).

Automated summary

This paper presents an additional mechanism for the evaporation of liquid drops and investigates the influences of disparities between the drop and vapor on the evaporation process. Experimental results demonstrate that the direction of evaporation is determined by vapor density and drop size, and a critical radius exists in oversaturated vapor, with smaller drops evaporating and larger drops acting as centers of condensation and growth.