Lee Jeong-Won, Ji Dae-Yun, Lee Kwon-Yeong, Hwang Woonbong
Department of Mechanical Engineering, Chosun University, Gwangju 61452, Republic of Korea.
Department of Mechanical and Control Engineering, Handong Global University, Pohang 37554, Republic of Korea.
ACS Omega. 2020 Oct 19;5(43):27880-27885. doi: 10.1021/acsomega.0c03081. eCollection 2020 Nov 3.
Enhancement in heat-transfer performance via dropwise condensation on superhydrophobic surfaces is much greater than that realized via generic condensation on a regular surface. However, if the supersaturation level during condensation increases above a specific value, water may seep to greater depths between structures. This may lead to attached condensation, which reduces condensation heat-transfer efficiency below that of ordinary surfaces. Therefore, it is critical to avoid the occurrence of supersaturation when superhydrophobic surfaces are employed in condenser design. The proposed study presents a simple method for regulating supersaturation on the laboratory scale. Experiments concerning droplet behavior on a superhydrophobic plate were performed to investigate droplet detachment and attachment in accordance with the surface and droplet temperatures. Results obtained have been represented as a ″droplet-behavior map″, which clearly depicts boundaries dividing the detachment and attachment regions. The supersaturation threshold obtained from the said map has been compared against results obtained from condensation heat-transfer experiments performed in an actual condenser environment. As observed, the two results demonstrate excellent agreement. Although superhydrophobicity of surfaces remains unchanged at room temperature, changes may occur in the extent of the supersaturation section, which improves condensation heat-transfer performance, depending on the surface-structure complexity. Therefore, droplet-behavior mapping has been used in this study to determine the available supersaturation section in accordance with the variation in surface roughness. Results confirm that the available supersaturation region increases with increasing surface roughness and structural complexity. Therefore, prior to applying superhydrophobicity to condensers, droplet-behavior mapping must be performed to avoid operation under the supersaturation conditions, which causes attached condensation.
通过超疏水表面上的滴状冷凝实现的传热性能增强远大于通过普通表面上的常规冷凝实现的传热性能增强。然而，如果冷凝过程中的过饱和度增加到特定值以上，水可能会渗入结构之间更深的深度。这可能会导致附着冷凝，从而使冷凝传热效率降低到普通表面以下。因此，在冷凝器设计中采用超疏水表面时，避免过饱和的发生至关重要。本研究提出了一种在实验室规模上调节过饱和度的简单方法。进行了关于超疏水板上液滴行为的实验，以根据表面和液滴温度研究液滴的脱离和附着。所获得的结果已表示为“液滴行为图”，该图清楚地描绘了划分脱离和附着区域的边界。从该图获得的过饱和阈值已与在实际冷凝器环境中进行的冷凝传热实验获得的结果进行了比较。如观察到的，这两个结果显示出极好的一致性。尽管表面的超疏水性在室温下保持不变，但根据表面结构的复杂性，过饱和部分的范围可能会发生变化，这会提高冷凝传热性能。因此，本研究中使用液滴行为映射来根据表面粗糙度的变化确定可用的过饱和部分。结果证实，可用的过饱和区域随着表面粗糙度和结构复杂性的增加而增加。因此，在将超疏水性应用于冷凝器之前，必须进行液滴行为映射，以避免在导致附着冷凝的过饱和条件下运行。
