The effect of relative humidity on dropwise condensation dynamics
The effect of relative humidity on dropwise condensation dynamics
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DOI：
10.1016/j.ijheatmasstransfer.2014.09.080
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发表时间：
2015
影响因子：
5.2
通讯作者：
J. E. Castillo;J. Weibel;S. Garimella
中科院分区：
文献类型：
--
作者：
J. E. Castillo;J. Weibel;S. Garimella
大气水蒸气的滴状冷凝在许多实际工程应用中是重要的。需要更好地理解环境因素和表面形态/化学对冷凝动力学的作用，以实现有效的集水、蒸发和其他干湿过程。可以促进更快的冷凝速率和冷凝液滴的自脱落的系统和表面可以导致在收获应用中改进的传质速率和更高的水产量。在本研究中，实验中进行的设施，允许可视化的冷凝过程中的垂直取向，疏水表面在受控的相对湿度和表面过冷温度。水滴的分布和生长在不同的相对湿度（45%，50%，55%和70%）下，在低于环境温度（20 °C）15 °C的恒定表面过冷温度下在整个表面上进行监测。液滴生长动力学表现出强烈的依赖于相对湿度的早期阶段，在此期间，有一个大的人口的小液滴的表面上和单个液滴的增长占主导地位的聚结效应。在后期阶段，由于聚结效应占主导地位，液滴生长的动力学对相对湿度不敏感。表面上的冷凝的总体积率也被评估为时间和环境相对湿度的函数。低相对湿度条件不仅降低了冷凝的绝对速率，而且延长了初始瞬态状态，在该初始瞬态状态下，冷凝速率保持显著低于稳态值。
Dropwise condensation of atmospheric water vapor is important in multiple practical engineering applications. The roles of environmental factors and surface morphology/chemistry on the condensation dynamics need to be better understood to enable efficient water-harvesting, dehumidification, and other psychrometric processes. Systems and surfaces that may promote faster condensation rates and self-shedding of condensate droplets could lead to improved mass transfer rates and higher water yields in harvesting applications. In the present study, experiments are performed in a facility that allows visualization of the condensation process on a vertically oriented, hydrophobic surface at a controlled relative humidity and surface subcooling temperature. The distribution and growth of water droplets are monitored across the surface at different relative humidities (45%, 50%, 55%, and 70%) at a constant surface subcooling temperature of 15 °C below the ambient temperature (20 °C). The droplet growth dynamics exhibits a strong dependency on relative humidity in the early stages during which there is a large population of small droplets on the surface and single droplet growth dominates over coalescence effects. At later stages, the dynamics of droplet growth is insensitive to relative humidity due to the dominance of coalescence effects. The overall volumetric rate of condensation on the surface is also assessed as a function of time and ambient relative humidity. Low relative humidity conditions not only slow the absolute rate of condensation, but also prolong an initial transient regime over which the condensation rate remains significantly below the steady-state value.