Electrowetting-based enhancement of droplet growth dynamics and heat transfer during humid air condensation
Electrowetting-based enhancement of droplet growth dynamics and heat transfer during humid air condensation
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DOI：
10.1016/j.ijheatmasstransfer.2019.05.112
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发表时间：
2019-09
影响因子：
5.2
通讯作者：
E. Wikramanayake;V. Bahadur
中科院分区：
文献类型：
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作者：
E. Wikramanayake;V. Bahadur
冷凝传热可以通过将蒸汽冷凝为液滴（而不是膜）来显著增强，液滴快速滚降。这项工作研究了使用电润湿来增强凝聚液滴的聚结、生长和滚降动力学，从而提高冷凝速率和相关的传热。这种增强取决于流体运动的性质（液滴的平移、三相线的振荡），而流体运动的性质又取决于所施加的电致动波形的幅度和频率。实验进行研究的早期阶段液滴生长动力学，以及稳态下的电场的影响下的冷凝。可以看出，随着AC电场的电压和频率的增加，液滴生长增强，AC电场比DC电场更有效。滚降动力学还取决于AC场的频率。总的来说，电场改变了液滴的尺寸分布，并将冷凝物移动到更有利的状态，以便从表面去除。冷凝速率取决于液滴的滚降直径、滚降事件的频率以及滚降液滴与其余液滴的相互作用。利用解析传热模型将测量的冷凝速率与冷凝传热联系起来。值得注意的是，这项研究涉及湿空气的冷凝，而不是纯蒸汽。总的来说，这项研究报告了超过30%的增强冷凝率所产生的外加电场，这突出了电润湿的吸引力冷凝传热增强。
Condensation heat transfer can be significantly enhanced by condensing vapor as droplets (instead of a film), which rapidly roll-off. This work studies the use of electrowetting to enhance coalescence, growth and roll-off dynamics of condensed droplets, thereby enhancing the condensation rate and associated heat transfer. This enhancement depends on the nature of fluid motion (translation of droplets, oscillations of the three phase line), which in turn depends on the magnitude and frequency of the applied electrical actuation waveform. Experiments are conducted to study early-stage droplet growth dynamics, as well as steady state condensation under the influence of an electric field. It is seen that droplet growth is enhanced as the voltage and frequency of AC electric fields is increased, with AC electric fields seen to be more effective than DC electric fields. Roll-off dynamics also depends on the frequency of the AC field. Overall, electric fields alter the droplet size distribution and move the condensate to more favorable states for removal from the surface. The condensation rate depends on the roll-off diameter of the droplet, frequency of roll-off events, and on the interactions of the rolled-off droplets with the remainder of the droplets. An analytical heat transfer model is utilized to relate the measured condensation rate with condensation heat transfer. It is noted that this study deals with condensation of humid air, and not pure steam. Overall, this study reports more than 30% enhancement in condensation rate resulting from the applied electric field, which highlights the attractiveness of electrowetting for condensation heat transfer enhancement.