AC electrowetting promoted droplet shedding on hydrophobic surfaces
AC electrowetting promoted droplet shedding on hydrophobic surfaces
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DOI：
10.1063/5.0006117
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发表时间：
2020-05
影响因子：
4
通讯作者：
E. Wikramanayake;J. Perry;V. Bahadur
中科院分区：
文献类型：
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作者：
E. Wikramanayake;J. Perry;V. Bahadur
通过将蒸汽冷凝为液滴（而不是膜），可以显著增强冷凝，液滴迅速脱落。电润湿（EW）诱导的聚结和脱落的液滴最近已被证明加速冷凝。本文研究了交流电润湿场对疏水表面液滴短时脱落的影响。实验涉及跟踪脱落的一个合奏的水滴的EW场的影响下，有三个参数被改变（电压，AC频率，和设备的几何形状）。获得了对EW诱导的液滴脱落的重要物理见解。首先，EW能够在非常短的持续时间（100 s）内几乎完全去除水（干燥区域分数> 98%）。第二，虽然干面积分数确实取决于所施加的电压，但是可以在不需要施加显著高于阈值电压的电压的情况下实现显著的水脱落。第三，AC波形的频率不影响干面积分数（对于高于阈值电压的电压）;然而，与液滴脱落相关联的时间常数强烈地取决于AC频率。第四，由于液滴的静电钉扎，装置的取向影响水的去除。重要的是，测得的水去除通量后立即应用的EW字段是两个数量级高于在一个长时间的冷凝实验测量，这突出了间歇性EW字段的好处，而不是连续的EW字段。总的来说，这些结果表明，在疏水表面上的EW提供的益处与超疏水表面提供的益处相当。
Condensation is significantly enhanced by condensing vapor as droplets (instead of a film), which rapidly shed-off. Electrowetting (EW)-induced coalescence and shedding of droplets have been recently shown to accelerate condensation. This work studies the influence of AC electrowetting fields on short-duration droplet shedding on hydrophobic surfaces. Experiments involve tracking the shedding of an ensemble of water droplets under the influence of EW fields, with three parameters being varied (voltage, AC frequency, and device geometry). Significant physical insights into EW-induced droplet shedding are obtained. First, EW enables almost complete removal of water (dry area fraction ∼98%) in very short time durations (∼ 1 s). Second, while the dry area fraction does depend on the applied voltage, significant water shedding can be achieved without needing to apply voltages significantly higher than the threshold voltage. Third, the frequency of the AC waveform does not influence the dry area fraction (for voltages above the threshold voltage); however the time constant associated with droplet shedding strongly depends on the AC frequency. Fourth, the orientation of the device influences water removal due to electrostatic pinning of droplets. Importantly, the measured water removal fluxes immediately after the application of an EW field are two orders of magnitude higher than those measured over a long-duration condensation experiment; this highlights the benefits of intermittent EW fields as opposed to continuous EW fields. Overall, these results suggest that EW on hydrophobic surfaces offers benefits comparable to those offered by superhydrophobic surfaces.