Quantifying vapor transfer into evaporating ethanol drops in a humid atmosphere
Quantifying vapor transfer into evaporating ethanol drops in a humid atmosphere
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DOI：
10.1039/c8cp02521e
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发表时间：
2018-08-07
影响因子：
3.3
通讯作者：
Sefiane, Khellil
中科院分区：
文献类型：
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作者：
Kita, Yutaku;Okauchi, Yuya;Sefiane, Khellil
研究了环境温度和相对湿度对乙醇液滴蒸发动力学的影响。虽然已经对混合物和纯流体的液滴蒸发进行了广泛的研究，但对大气中存在的第二组分转移后从纯流体到二元混合物的转变知之甚少。这对于工业、生物和医学应用非常重要，因为溶剂的纯度是至关重要的。在蒸发过程中，通过及时直接定量液滴的组成，呈现了水的吸附-吸收和/或凝结成乙醇滴。特别地，我们将液滴剖面测量与气相进样色谱（GIC）相结合，直接量化乙醇蒸发的量和随时间的进水量。正如预期的那样，由于乙醇饱和浓度和蒸汽扩散系数与温度成正比，液滴在较高的温度下蒸发得更快。另一方面，在较高的相对湿度下，观察到乙醇蒸发速率和进水量的增加。在较高的相对湿度下，乙醇蒸发的增加可以解释为乙醇在潮湿空气中的扩散系数大于干燥空气。此外，由于乙醇在高湿环境中蒸发，与低湿条件相比，由于蒸发冷却和水凝结，液滴界面温度降至露点以下。由于吸附-吸收和/或冷凝释放的热量，据红外热像仪证实，液-气界面处的温度更高，导致表面乙醇饱和浓度更高，因此蒸发的驱动力更大。通过将液滴轮廓与液滴内乙醇和水的组成相结合，我们提出了蒸发-吸附/吸收和/或冷凝的联合经验关联。所提出的相关性考虑了：由于水的吸附-吸收和/或凝结而导致的乙醇浓度的降低，相对湿度对扩散系数的依赖，以及蒸发过程中的吸水量。所提出的经验相关性与实验观察结果非常吻合。
The effect of ambient temperature and relative humidity on the dynamics of ethanol drop evaporation is investigated. Although drop evaporation of mixtures and pure fluids has been extensively studied, very little is known about the transition from a pure fluid to a binary mixture following transfer of a second component present in the atmosphere. This is of importance for industrial, biological and medical applications where the purity of the solvent is paramount. Adsorption-absorption and/or condensation of water into ethanol drops during evaporation is presented through direct quantification of the drop composition in time. In particular, we combine drop profile measurements with Gas Injection Chromatography (GIC) to directly quantify the amount of ethanol evaporated and that of water intake over time. As expected, drops evaporate faster at higher temperatures since both the ethanol saturation concentration and the vapor diffusion coefficient are directly proportional to temperature. On the other hand, increases in the ethanol evaporation rate and in the water intake are observed at higher relative humidity. The increase in ethanol evaporation at higher relative humidity is interpreted by the greater diffusion coefficient of ethanol into humid air when compared to dry air. Moreover, as ethanol evaporates in a high humidity environment, the drop interfacial temperature falls below the dew point due to evaporative cooling and water condenses compared to lower humidity conditions. As a consequence of the heat released by adsorption-absorption and/or condensation, a greater temperature is reported at the liquid-vapor interface as confirmed by IR thermography, inducing a greater ethanol saturation concentration at the surface and hence a greater driving force for evaporation. By coupling the drop profile and the composition of ethanol and water within the drop, we propose a combined evaporation-adsorption/absorption and/or condensation empirical correlation. The proposed correlation accounts for: the decreases in ethanol concentration due to water adsorption-absorption and/or condensation, the diffusion coefficient dependence on relative humidity, and the amount of water intake during evaporation. The proposed empirical correlation agrees remarkably well with experimental observations.