Abstract Previous studies of droplet spreading on superhydrophilic nanostructured surfaces have demonstrated that enhanced wetting and wickability of such surfaces can produce more rapid and extensive spreading of liquid droplets. There is also ample evidence from prior studies that these types of superhydrophilic nanostructured surfaces can exhibit enhanced vaporization heat transfer performance in for droplet evaporation and pool boiling processes. This study specifically explored the mechanisms of droplet vaporization on superhydrophilic nanoporous thin layers, at a fundamental level, for conditions in which liquid viscous forces and pore capillarity forces dominate, and liquid inertia forces are low. The investigation, summarized here, experimentally explored the droplet evaporation heat transfer performance on superhydrophilic, nanoporous, thin layers on a heated metal substrate. A thermal growth process was used to fabricate a layer of ZnO nanopillars a few microns thick on a copper substrate. The resulting nanoporous layer exhibited ultra-low contact angles and high wickability. The experiments indicate that, on these surfaces, a deposited droplet undergoes an initial rapid spreading phase followed by a slower vaporization phase, which shrinks the droplet until evaporation is complete. Although droplet evaporation without bubble nucleation is the primary focus of this work, the experiments also examined the added effects of bubble nucleation on droplet evaporation at high surface superheats. Based on experimental observations and data, a model of heat transport during the evaporation process was developed. The model predictions are shown to agree well with droplet evaporation time measurements for droplets of different initial sizes and a range of surface temperatures. The experiments and model indicate that the surfaces tested enhance droplet evaporation heat transfer performance by as much as a factor of three compared to an ordinary copper surface at the same conditions. The model is also used to explore the potential for more extreme augmentation of droplet evaporation heat transfer by further enhancement of surface wetting and wickability. The results of this study provide a clearer picture of the interconnection of droplet spreading mechanisms and evaporation heat transfer for these circumstances.

中文翻译：

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用于在超亲水薄纳米多孔层上蒸发液滴的热传输

摘要先前在超亲水纳米结构表面上扩散的研究表明，这种表面的润湿性和芯吸性增强可以产生更快速和更广泛的液滴扩散。先前的研究也有充分的证据表明，这些类型的超亲水纳米结构表面可以在液滴蒸发和池沸腾过程中表现出增强的蒸发传热性能。本研究在基本层面上专门探讨了液滴在超亲水纳米多孔薄层上汽化的机制，适用于液体粘性力和孔毛细作用力占主导地位且液体惯性力较低的条件。在此总结的研究通过实验探索了超亲水、纳米多孔、加热金属基板上的薄层。使用热生长工艺在铜基板上制造了几微米厚的 ZnO 纳米柱层。所得纳米多孔层表现出超低接触角和高芯吸能力。实验表明，在这些表面上，沉积的液滴经历了最初的快速扩散阶段，然后是较慢的汽化阶段，这使液滴收缩，直到蒸发完成。尽管没有气泡成核的液滴蒸发是这项工作的主要焦点，但实验还检查了气泡成核对高表面过热度下液滴蒸发的附加影响。根据实验观察和数据，开发了蒸发过程中的热传递模型。模型预测与不同初始尺寸和一系列表面温度的液滴的液滴蒸发时间测量结果非常吻合。实验和模型表明，与相同条件下的普通铜表面相比，所测试的表面将液滴蒸发传热性能提高了三倍之多。该模型还用于通过进一步增强表面润湿性和芯吸性来探索更极端地增加液滴蒸发传热的潜力。这项研究的结果提供了在这些情况下液滴扩散机制和蒸发热传递之间相互联系的更清晰的画面。实验和模型表明，与相同条件下的普通铜表面相比，测试的表面将液滴蒸发传热性能提高了三倍。该模型还用于通过进一步增强表面润湿性和芯吸性来探索更极端地增加液滴蒸发传热的潜力。这项研究的结果提供了在这些情况下液滴扩散机制和蒸发热传递之间相互联系的更清晰的画面。实验和模型表明，与相同条件下的普通铜表面相比，所测试的表面将液滴蒸发传热性能提高了三倍之多。该模型还用于通过进一步增强表面润湿性和芯吸性来探索更极端地增加液滴蒸发传热的潜力。这项研究的结果提供了在这些情况下液滴扩散机制和蒸发热传递之间相互联系的更清晰的画面。该模型还用于通过进一步增强表面润湿性和芯吸性来探索更极端地增加液滴蒸发传热的潜力。这项研究的结果提供了在这些情况下液滴扩散机制和蒸发热传递之间相互联系的更清晰的画面。该模型还用于通过进一步增强表面润湿性和芯吸性来探索更极端地增加液滴蒸发传热的潜力。这项研究的结果提供了在这些情况下液滴扩散机制和蒸发热传递之间相互联系的更清晰的画面。