Department of Mechanical and Aerospace Engineering, Syracuse University, Syracuse, New York 13244, United States.
ACS Appl Mater Interfaces. 2023 May 3;15(17):21679-21689. doi: 10.1021/acsami.3c02450. Epub 2023 Apr 20.
Durability of a lubricant-infused surface (LIS) is critical for heat transfer, especially in condensation-based applications. Although LIS promotes dropwise condensation, each departing droplet condensate acts as a lubricant-depleting agent due to the formation of wetting ridge and cloaking layer around the condensate, thus gradually leading to drop pinning on the underlying rough topography. Condensation heat transfer further deteriorates in the presence of non-condensable gases (NCGs) requiring special experimental arrangements to eliminate NCGs due to a decrease in the availability of nucleation sites. To address these issues while simultaneously improving heat-transfer performance of LIS in condensation-based systems, we report fabrication of both fresh LIS and a lubricant-depleted LIS using silicon porous nanochannel wicks as an underlying substrate. Strong capillarity in the nanochannels helps retain silicone oil (polydimethylsiloxane) on the surface even after it is severely depleted under tap water. The effect of oil viscosity was investigated for drop mobility and condensation heat transfer under ambient conditions, i.e., in the presence of NCGs. While fresh LIS prepared using 5 cSt silicone oil exhibited a low roll-off angle (∼1°) and excellent water drop (5 μL) sliding velocity ∼66 mm s, it underwent rapid depletion as compared to higher viscosity oils. Condensation performed on depleted nanochannel LIS with higher viscosity oil (50 cSt) resulted in a heat-transfer coefficient (HTC) of ∼2.33 kW m K, which is a ∼162% improvement over flat Si-LIS (50 cSt). Such LIS promote fast drop shedding as is evident from the little change in the fraction of drops with diameter <500 μm from ∼98% to only ∼93% after 4 h of condensation. Improvement in HTC was also seen in condensation experiments conducted for 3 days where a steady HTC of ∼1.46 kW m K was achieved over the last 2 days. The ability of reported LIS to maintain long-term hydrophobicity and dropwise condensation will aid in designing condensation-based systems with improved heat-transfer performance.
在基于冷凝的应用中，润湿性表面（LIS）的耐久性对于热传递至关重要。尽管 LIS 促进了点滴冷凝，但由于在冷凝周围形成了润湿脊和包络层，每个离开的液滴冷凝物都会充当耗尽润滑剂的试剂，从而逐渐导致液滴在下面的粗糙表面上被固定。由于凝结核数目的减少，存在不凝性气体（NCG）时，冷凝传热会进一步恶化，需要特殊的实验装置来消除 NCG。为了解决这些问题，同时提高基于冷凝的系统中 LIS 的传热性能，我们报告了使用硅多孔纳米通道芯吸作为底层衬底来制造新鲜的 LIS 和耗尽润滑剂的 LIS。纳米通道中的强毛细作用有助于在表面上保留硅油（聚二甲基硅氧烷），即使在严重耗尽的情况下，也能保留硅油（聚二甲基硅氧烷）。在环境条件下（即存在 NCG 时），研究了油粘度对液滴迁移和冷凝传热的影响。使用 5 cSt 硅油制备的新鲜 LIS 表现出低滚落角度（约 1°）和优异的水滴（5 μL）滑动速度约 66 mm s，但与高粘度油相比，它的消耗速度更快。在具有较高粘度油（50 cSt）的耗尽纳米通道 LIS 上进行的冷凝导致传热系数（HTC）约为 2.33 kW m K，与平坦 Si-LIS（50 cSt）相比提高了约 162%。这种 LIS 促进了快速的液滴脱落，从冷凝 4 小时后直径<500 μm的液滴分数从约 98%变化到仅约 93%就可以明显看出。在进行了 3 天的冷凝实验中，HTC 也得到了改善，在最后 2 天中实现了约 1.46 kW m K 的稳定 HTC。所报道的 LIS 保持长期疏水性和点滴冷凝的能力将有助于设计具有改进传热性能的基于冷凝的系统。
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