Effect of the Size of the Superhydrophobic Regions of Biphilic Surfaces on the Bubble Dynamics
The current work aims to experimentally evaluate the effect of the size of circular superhydrophobic regions of biphilic surfaces on the bubble dynamics under pool boiling conditions. Biphilic surfaces are structured surfaces with tunable wettability, presenting an array of hydrophobic small spots i...
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| Format: | Article |
| Language: | English |
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MDPI AG
2023-04-01
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| Series: | Symmetry |
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| Online Access: | https://www.mdpi.com/2073-8994/15/4/949 |
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| author | José Pereira Ricardo Cautela Ana Moita António Moreira |
| author_facet | José Pereira Ricardo Cautela Ana Moita António Moreira |
| author_sort | José Pereira |
| collection | DOAJ |
| description | The current work aims to experimentally evaluate the effect of the size of circular superhydrophobic regions of biphilic surfaces on the bubble dynamics under pool boiling conditions. Biphilic surfaces are structured surfaces with tunable wettability, presenting an array of hydrophobic small spots in a hydrophilic surface or vice versa. The factors that affect the bubble dynamics are of geometric nature such as the diameters of the bubbles, their volume, and the height of the centroid, and of more complex nature such as the departure frequency of the bubbles and the rate of evaporation mass transfer. In this study, the bubble dynamics and boiling performance were evaluated by adjusting the diameter of the single circular superhydrophobic regions. A stainless steel AISI 304 foil was used as the base hydrophilic region, and the superhydrophobic regions were made by spray coating the NeverWet<sup>®</sup> superhydrophobic solution over well-defined masks. The main conclusion was that the bubble dynamics are clearly affected by the diameter of the superhydrophobic spots. The smaller spots favored the generation of more uniform and stable bubbles, mainly due to the border surface tension forces’ dominance. With the increase in the diameter of the bubbles, the surface tension acting at the border with the much larger hydrophilic region impacts the process less. Thus, the smaller superhydrophobic regions had higher evaporation mass transfer rates. The region with the best pool boiling performance along with improved bubble dynamics was the superhydrophobic region with an 0.8 mm diameter, corresponding to a superhydrophobic area to total area ratio of 0.11%. Moreover, this experimental work confirmed that the bubble dynamics’ impacting factors such as the diameter at the various stages of development of the bubbles can be modulated according to the final objectives of the design and fabrication of the biphilic surfaces. The research significance and novelty of this work come from the comprehensive study of the geometrical pattern of the heat transfer surface in pool boiling conditions and its impact on the bubble dynamics and heat transfer capability. We also suggest further studies considering nanoscale superhydrophobic spot arrangements and the future usage of different working fluids such as nanofluids. |
| first_indexed | 2024-03-11T04:29:12Z |
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| issn | 2073-8994 |
| language | English |
| last_indexed | 2024-03-11T04:29:12Z |
| publishDate | 2023-04-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Symmetry |
| spelling | doaj.art-8b825db775564dbc84d732c1962e7cfe2023-11-17T21:35:01ZengMDPI AGSymmetry2073-89942023-04-0115494910.3390/sym15040949Effect of the Size of the Superhydrophobic Regions of Biphilic Surfaces on the Bubble DynamicsJosé Pereira0Ricardo Cautela1Ana Moita2António Moreira3IN+ Center for Innovation, Technology and Policy Research, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, PortugalIN+ Center for Innovation, Technology and Policy Research, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, PortugalIN+ Center for Innovation, Technology and Policy Research, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, PortugalIN+ Center for Innovation, Technology and Policy Research, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, PortugalThe current work aims to experimentally evaluate the effect of the size of circular superhydrophobic regions of biphilic surfaces on the bubble dynamics under pool boiling conditions. Biphilic surfaces are structured surfaces with tunable wettability, presenting an array of hydrophobic small spots in a hydrophilic surface or vice versa. The factors that affect the bubble dynamics are of geometric nature such as the diameters of the bubbles, their volume, and the height of the centroid, and of more complex nature such as the departure frequency of the bubbles and the rate of evaporation mass transfer. In this study, the bubble dynamics and boiling performance were evaluated by adjusting the diameter of the single circular superhydrophobic regions. A stainless steel AISI 304 foil was used as the base hydrophilic region, and the superhydrophobic regions were made by spray coating the NeverWet<sup>®</sup> superhydrophobic solution over well-defined masks. The main conclusion was that the bubble dynamics are clearly affected by the diameter of the superhydrophobic spots. The smaller spots favored the generation of more uniform and stable bubbles, mainly due to the border surface tension forces’ dominance. With the increase in the diameter of the bubbles, the surface tension acting at the border with the much larger hydrophilic region impacts the process less. Thus, the smaller superhydrophobic regions had higher evaporation mass transfer rates. The region with the best pool boiling performance along with improved bubble dynamics was the superhydrophobic region with an 0.8 mm diameter, corresponding to a superhydrophobic area to total area ratio of 0.11%. Moreover, this experimental work confirmed that the bubble dynamics’ impacting factors such as the diameter at the various stages of development of the bubbles can be modulated according to the final objectives of the design and fabrication of the biphilic surfaces. The research significance and novelty of this work come from the comprehensive study of the geometrical pattern of the heat transfer surface in pool boiling conditions and its impact on the bubble dynamics and heat transfer capability. We also suggest further studies considering nanoscale superhydrophobic spot arrangements and the future usage of different working fluids such as nanofluids.https://www.mdpi.com/2073-8994/15/4/949heat transfernucleate boilingbiphilic surfacesbubble dynamics |
| spellingShingle | José Pereira Ricardo Cautela Ana Moita António Moreira Effect of the Size of the Superhydrophobic Regions of Biphilic Surfaces on the Bubble Dynamics Symmetry heat transfer nucleate boiling biphilic surfaces bubble dynamics |
| title | Effect of the Size of the Superhydrophobic Regions of Biphilic Surfaces on the Bubble Dynamics |
| title_full | Effect of the Size of the Superhydrophobic Regions of Biphilic Surfaces on the Bubble Dynamics |
| title_fullStr | Effect of the Size of the Superhydrophobic Regions of Biphilic Surfaces on the Bubble Dynamics |
| title_full_unstemmed | Effect of the Size of the Superhydrophobic Regions of Biphilic Surfaces on the Bubble Dynamics |
| title_short | Effect of the Size of the Superhydrophobic Regions of Biphilic Surfaces on the Bubble Dynamics |
| title_sort | effect of the size of the superhydrophobic regions of biphilic surfaces on the bubble dynamics |
| topic | heat transfer nucleate boiling biphilic surfaces bubble dynamics |
| url | https://www.mdpi.com/2073-8994/15/4/949 |
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