Analyzing Interfacial Transport for Water Evaporating into Dry Nitrogen
Analyzing Interfacial Transport for Water Evaporating into Dry Nitrogen
复制标题
DOI：
10.1016/j.applthermaleng.2021.117910
复制
发表时间：
2021-12
影响因子：
6.4
通讯作者：
Brandon Murray;M. Fox;Shankar Narayan
中科院分区：
文献类型：
--
作者：
Brandon Murray;M. Fox;Shankar Narayan
设计工业应用的空气-水系统需要对气液界面的质量迁移率有一个基本的了解，这取决于许多因素，包括温度、蒸汽浓度和随时间变化的杂质。因此，了解质量调节如何随液滴的寿命变化，对于预测利用蒸发的应用程序的性能至关重要。在本研究中，将镀金表面水滴蒸发成干氮气的实验数据与计算模型相耦合，以测量汽液界面的调节系数。我们通过结合宏观观测和气体的微观动力学理论来进行这项测量。实验中利用灵敏的压电式器件精确测定液滴半径，并利用成像技术测量液滴接触角。这一设置还对液滴中痕量的非挥发性杂质进行了定量。对于在纯氮气气流中蒸发的水滴，调节系数直接与液滴表面的水蒸气通量有关，并受到杂质存在的影响。我们得到了接近室温蒸发的多个水滴的表面平均调节系数接近0.001。这种量化可以帮助进行更准确的蒸发分析，这可以帮助改进基于蒸发的应用程序的设计。我们相信，本文提出的将气体动力学理论与宏观流动行为相结合的建模方法，可以为在极端干燥的不可凝结气流存在的情况下预测蒸发动力学提供基础。
Designing air-water systems for industrial applications requires a fundamental understanding of mass accommodation at the liquid-vapor interface, which depends on many factors, including temperature, vapor concentration, and impurities that vary with time. Hence, understanding how mass accommodation changes over a droplet’s lifespan is critical for predicting the performance of applications leveraging evaporation. In this study, experimental data of water droplets on a gold-coated surface evaporating into dry nitrogen is coupled with a computational model to measure the accommodation coefficient at the liquid-vapor interface. We conduct this measurement by combining macroscopic observations with the microscopic kinetic theory of gasses. The experiments utilize a sensitive piezoelectric device to determine the droplet radius with high accuracy and imaging to measure the droplet contact angle. This setup also quantifies the trace amounts of non-volatile impurities in the droplet. For water droplets evaporating in a pure nitrogen stream, the accommodation coefficient directly relates to vapor flux over the droplet’s surface and is affected by the presence of impurities. We obtained a surface-averaged accommodation coefficient close to 0.001 across multiple water droplets evaporating close to room temperature. This quantification can aid in conducting a more accurate analysis of evaporation, which can assist in the improved design of evaporation-based applications. We believe the modeling approach presented in this work, which integrates the kinetic theory of gases to the macroscale flow behavior, can provide a basis for predicting evaporation kinetics in the presence of extremely dry non-condensable gas streams.