Limited Enhancement of Subatmospheric Boiling on Treated Structured Surfaces with Biphilic Pattern
Limited Enhancement of Subatmospheric Boiling on Treated Structured Surfaces with Biphilic Pattern
复制标题
具有双亲模式的处理过的结构化表面上的低于常压沸腾的有限增强
DOI：
10.1115/1.4051056
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Takata Yasuyuki
中科院分区：
文献类型：
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作者：
Shen Biao;Iwata Naoki;Hidaka Sumitomo;Takahashi Koji;Takata Yasuyuki
沸腾换热在亚大气条件下恶化，这可以归因于在下降压力下缺乏可行的成核点。在这项工作中，实验探索了结合润湿性图案化和结构修饰来增强水的低压饱和沸腾的可能性。铜测试表面由一系列圆形“酒窝”(深度为0.3 mm，直径为0.5 mm，节距为3.0 mm)组成，表面喷涂聚四氟乙烯涂层，以便与表面空腔形成匹配的双亲图案。与平坦的双亲表面相比，核态沸腾的平均换热系数最大提高了60%，降低到约9.5kPa. 。然而，进一步将压力降低到7.8kpa 会导致性能收益减少。气泡脱离动力学的可视化研究揭示了疏水涂层空腔的额外蒸汽捕集迹象，这可以在零等待时间内诱导不间断的气泡再生，并解释了亚常压沸腾的合格强化。由于疏水腔内接触线的潜在二次钉扎，在比没有酒窝结构的情况下更低的压力下，不完全气泡脱离可能占上风，留下明显更多的蒸汽残留物。然而，发现蒸汽捕集能力随着压力的增加而降低，这为表面在更低压力下的效率降低提供了线索。
Boiling heat transfer suffers deteriorations under subatmospheric conditions, which can be attributed to a shortage of viable nucleation sites at declining pressures. In this work, the possibility of enhancing low-pressure saturated boiling of water using a combination of wettability patterning and structural modifications was experimentally explored. The copper test surface, comprised of an array of circular “dimples” (0.3 mm in depth, 0.5 mm in diameter, and 3.0 mm in pitch), was spray-coated by polytetrafluoroethylene (PTFE) coatings so as to form a matching biphilic pattern with the surface cavities. The resulting dimpled biphilic surface showed appreciable heat transfer enhancement—with a maximum 60% increase of the average heat transfer coefficient of nucleate boiling compared with a flat biphilic surface—down to about 9.5 kPa. Further lowering the pressure to 7.8 kPa, however, was found to lead to diminished performance gains. The visualization study of the bubble departure dynamics revealed signs of additional vapor trapping of the hydrophobic-coated cavities, which can induce uninterrupted bubble regeneration with zero waiting time and explain the qualified enhancement of subatmospheric boiling. Thanks to a potential secondary pinning of contact line inside the hydrophobic cavities, incomplete bubble detachment could prevail at somewhat lower pressures than was otherwise possible without the dimple structure, leaving behind significantly more vapor residues. However, the vapor-trapping capacity was found to decrease with pressure, which provided clues with regard to the reduced efficacy of the surface at even lower pressures.