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arXiv 2109.01459physics.flu-dyncond-mat.soft
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液滴在同一流体的蒸汽中漂浮的动力学

Dynamics of a drop floating in vapor of the same fluid

E. S. Benilov

摘要:

被相同流体的蒸气或蒸气和空气包围的液滴的蒸发通常归因于蒸气扩散-然而,这不适用于前一种设置,因为纯流体不扩散。本文件提出了一个适用于这两种情况的补充机制。它示出的下降和蒸汽之间的差异,在他们的压力和化学势引起的流动。它的方向取决于蒸汽密度和液滴的大小。在不饱和或饱和的蒸汽中,所有的液滴都会蒸发,但在过饱和(但热力学稳定)的蒸汽中,存在一个临界半径:较小的液滴蒸发,较大的液滴作为冷凝中心并生长。所开发的模型是用来估计的蒸发时间的一滴漂浮在饱和蒸汽。结果表明,如果汽液密度比很小,蒸发通量也很小--因此,毫米大小的水滴在低于$70^{\circ}\mathrm{C}$的温度下可以存活数天。然而,如果温度与其临界值相当(但不一定接近),这些液滴会在几分钟内蒸发。反过来,对于三相点和临界点之间的所有温度,100微米大小的液滴都会在几秒钟内蒸发。

英文摘要:

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, 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 $70^{\circ}\mathrm{C}$ 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.

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