Electric-Field-Enhanced Condensation on Superhydrophobic Nanostructured Surfaces
When condensed droplets coalesce on a superhydrophobic nanostructured surface, the resulting droplet can jump due to the conversion of excess surface energy into kinetic energy. This phenomenon has been shown to enhance condensation heat transfer by up to 30% compared to state-of-the-art dropwise co...
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| Format: | Article |
| Language: | en_US |
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American Chemical Society (ACS)
2015
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| Online Access: | http://hdl.handle.net/1721.1/92838 https://orcid.org/0000-0001-7045-1200 |
| _version_ | 1811094029824163840 |
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| author | Miljkovic, Nenad Enright, Ryan Wang, Evelyn N. Preston, Daniel John |
| author2 | Massachusetts Institute of Technology. Department of Mechanical Engineering |
| author_facet | Massachusetts Institute of Technology. Department of Mechanical Engineering Miljkovic, Nenad Enright, Ryan Wang, Evelyn N. Preston, Daniel John |
| author_sort | Miljkovic, Nenad |
| collection | MIT |
| description | When condensed droplets coalesce on a superhydrophobic nanostructured surface, the resulting droplet can jump due to the conversion of excess surface energy into kinetic energy. This phenomenon has been shown to enhance condensation heat transfer by up to 30% compared to state-of-the-art dropwise condensing surfaces. However, after the droplets jump away from the surface, the existence of the vapor flow toward the condensing surface increases the drag on the jumping droplets, which can lead to complete droplet reversal and return to the surface. This effect limits the possible heat transfer enhancement because larger droplets form upon droplet return to the surface, which impedes heat transfer until they can be either removed by jumping again or finally shedding via gravity. By characterizing individual droplet trajectories during condensation on superhydrophobic nanostructured copper oxide (CuO) surfaces, we show that this vapor flow entrainment dominates droplet motion for droplets smaller than R ≈ 30 μm at moderate heat fluxes (q″ > 2 W/cm2). Subsequently, we demonstrate electric-field-enhanced condensation, whereby an externally applied electric field prevents jumping droplet return. This concept leverages our recent insight that these droplets gain a net positive charge due to charge separation of the electric double layer at the hydrophobic coating. As a result, with scalable superhydrophobic CuO surfaces, we experimentally demonstrated a 50% higher overall condensation heat transfer coefficient compared to that on a jumping-droplet surface with no applied field for low supersaturations (<1.12). This work not only shows significant condensation heat transfer enhancement but also offers avenues for improving the performance of self-cleaning and anti-icing surfaces as well as thermal diodes. |
| first_indexed | 2024-09-23T15:54:23Z |
| format | Article |
| id | mit-1721.1/92838 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T15:54:23Z |
| publishDate | 2015 |
| publisher | American Chemical Society (ACS) |
| record_format | dspace |
| spelling | mit-1721.1/928382022-09-29T16:55:27Z Electric-Field-Enhanced Condensation on Superhydrophobic Nanostructured Surfaces Miljkovic, Nenad Enright, Ryan Wang, Evelyn N. Preston, Daniel John Massachusetts Institute of Technology. Department of Mechanical Engineering Miljkovic, Nenad Miljkovic, Nenad Enright, Ryan Preston, Daniel John Wang, Evelyn N. When condensed droplets coalesce on a superhydrophobic nanostructured surface, the resulting droplet can jump due to the conversion of excess surface energy into kinetic energy. This phenomenon has been shown to enhance condensation heat transfer by up to 30% compared to state-of-the-art dropwise condensing surfaces. However, after the droplets jump away from the surface, the existence of the vapor flow toward the condensing surface increases the drag on the jumping droplets, which can lead to complete droplet reversal and return to the surface. This effect limits the possible heat transfer enhancement because larger droplets form upon droplet return to the surface, which impedes heat transfer until they can be either removed by jumping again or finally shedding via gravity. By characterizing individual droplet trajectories during condensation on superhydrophobic nanostructured copper oxide (CuO) surfaces, we show that this vapor flow entrainment dominates droplet motion for droplets smaller than R ≈ 30 μm at moderate heat fluxes (q″ > 2 W/cm2). Subsequently, we demonstrate electric-field-enhanced condensation, whereby an externally applied electric field prevents jumping droplet return. This concept leverages our recent insight that these droplets gain a net positive charge due to charge separation of the electric double layer at the hydrophobic coating. As a result, with scalable superhydrophobic CuO surfaces, we experimentally demonstrated a 50% higher overall condensation heat transfer coefficient compared to that on a jumping-droplet surface with no applied field for low supersaturations (<1.12). This work not only shows significant condensation heat transfer enhancement but also offers avenues for improving the performance of self-cleaning and anti-icing surfaces as well as thermal diodes. United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-FG02-09ER46577) United States. Office of Naval Research National Science Foundation (U.S.). Graduate Research Fellowship (Grant 1122374) Irish Research Council for Science, Engineering, and Technology 2015-01-13T20:48:15Z 2015-01-13T20:48:15Z 2013-11 2013-09 Article http://purl.org/eprint/type/JournalArticle 1936-0851 1936-086X http://hdl.handle.net/1721.1/92838 Miljkovic, Nenad, Daniel J. Preston, Ryan Enright, and Evelyn N. Wang. “Electric-Field-Enhanced Condensation on Superhydrophobic Nanostructured Surfaces.” ACS Nano 7, no. 12 (December 23, 2013): 11043–11054. https://orcid.org/0000-0001-7045-1200 en_US http://dx.doi.org/10.1021/nn404707j ACS Nano Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf American Chemical Society (ACS) Nenad Miljkovic |
| spellingShingle | Miljkovic, Nenad Enright, Ryan Wang, Evelyn N. Preston, Daniel John Electric-Field-Enhanced Condensation on Superhydrophobic Nanostructured Surfaces |
| title | Electric-Field-Enhanced Condensation on Superhydrophobic Nanostructured Surfaces |
| title_full | Electric-Field-Enhanced Condensation on Superhydrophobic Nanostructured Surfaces |
| title_fullStr | Electric-Field-Enhanced Condensation on Superhydrophobic Nanostructured Surfaces |
| title_full_unstemmed | Electric-Field-Enhanced Condensation on Superhydrophobic Nanostructured Surfaces |
| title_short | Electric-Field-Enhanced Condensation on Superhydrophobic Nanostructured Surfaces |
| title_sort | electric field enhanced condensation on superhydrophobic nanostructured surfaces |
| url | http://hdl.handle.net/1721.1/92838 https://orcid.org/0000-0001-7045-1200 |
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