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Dropwise condensation is well known to result in better heat transfer performance owing to efficient condensate/droplet removal, which can be harnessed in various industrial heat/mass transfer applications such as power generation and conversion, water harvesting/desalination, and electronics thermal management. The key to enhancing condensation via the dropwise mode is thin low surface energy coatings (<100 nm) with low contact angle hysteresis. Ultrathin (<5 nm) silane self assembled monolayers (or SAMs) have been widely studied to promote dropwise condensation due to their minimal thermal resistance and scalable integration processes. Such thin coatings typically degrade within an hour during condensation of water vapor. After coating failure, water vapor condensation transitions to the inefficient filmwise mode with poor heat transfer performance. We enhance silane SAM quality and durability during water vapor condensation on copper compared to state of the art silane coatings on metal surfaces. We achieve this via (i) surface polishing to sub-10 nm levels, (ii) pure oxygen plasma surface treatment, and (iii) silane coating integration with the copper substrate in an anhydrous/moisture-free environment. The resulting silane SAM has low contact angle hysteresis (≈20°) and promotes efficient dropwise condensation of water for >360 hours without any visible sign of coating failure/degradation in the absence of non condensable gases. We further demonstrate enhanced heat transfer performance (≈5 7× increase over filmwise condensation) over an extended period of time. Surface characterization data post-condensation leads us to propose that in the absence of non-condensable gases in the vapor environment, the silane SAM degrades due to reduction and subsequent dissolution of copper oxide at the oligomer-substrate interface. The experiments also indicate that the magnitude of surface subcooling (or condensation rate) affects the rate of coating degradation. This work identifies a pathway to durable dropwise promoter coatings that will enable efficient heat transfer in industrial applications.
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Field tests of a self-sintering, anti-soiling, self-cleaning, nanoporous metal oxide, transparent thin film coating for solar photovoltaic modules
Nanoporous metal oxide ceramic coatings, deposited using sol-gel techniques, have the potential to impart self-sintering and self-cleaning coatings to silicon oxide glass. When used on solar photovoltaic modules, these coatings can impart anti-static properties, improve wetting behavior, and degrade soiling deposits through photocatalytic activity. This paper reports on a field trial of a mixed silicon and titanium oxide thin film coating conducted in the upper midwestern U.S. Coated modules demonstrated increased electrical generation relative to uncoated controls. The results are encouraging for the commercialization of this coating technology, and provide a strong motivation for further research and development efforts.
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- PAR ID:
- 10499615
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Solar Energy Materials and Solar Cells
- Volume:
- 262
- Issue:
- C
- ISSN:
- 0927-0248
- Page Range / eLocation ID:
- 112560
- Subject(s) / Keyword(s):
- Solar Soiling Self-cleaning Coating Nanoporous Sol-gel
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.solmat.2023.112560
