2016 Fiscal Year Research-status Report
Effect of Micro-/Nano-patterned Wettability on the Fundamentals of Condensation Heat Transfer
| Project/Area Number |
16K18029
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| Research Institution | Kyushu University |
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Principal Investigator |
オレホン ダニエル 九州大学, カーボンニュートラル・エネルギー国際研究所, 助教 (40726246)
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| Project Period (FY) |
2016-04-01 – 2018-03-31
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| Keywords | Dropwise Condensation / Filmwise Condensation / Microstructured Surfaces / Liquid Propagation / Simultaneous DWC/FWC / Hydrophilic / Superhydrophobic / Condensation Dynamics |
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| Outline of Annual Research Achievements |
A novel Simultaneous Dropwise and Filwise Condensation behavior has been demonstrated on a hydrophilic microstructured surface. For a fixed micropillar aspect ratio (same height/diameter), by varying the micropillar spacing I am able to induce a different condensation behavior. For large spacing between pillars condensation takes place initially as dropwise condensation and as condensation develops, the condensate overcomes the micropillars height and condensation continues in a filmwise fashion. On the other hand, in the case of short spacing between pillars, I am able to constrain the condensate between the microstructures and the raise of the condensate interface above the microstructures is not thermodynamically favorable. In this case, filmwise condensation between pillars and the continuous nucleation, growth and departure of droplets in the order of tenths of micrometers is reported. It is the first time that continuous dropwise condensation is realized in a hydrophilic surface without the assistance of a hydrophobic coating. The greater heat transfer of simultaneous dropwise/filmwise condensation behavior is also demonstrated.
In addition the effect of microstructures present on superhydrophobic surfaces is being investigated by a custom built optical microscope. I have found that the presence of microstructures hinders the coalescence-induced droplet-jumping. It is the first time that the effect of microstructures on solely droplet jumping phenomenon on a superhydrophobic surface is reported.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The work is going very well, however collaboration and interactions with York University is being quite weak. York University and Professor Mitra were in charge of facilitating the micropillared surfaces for this study, however they are facing several problems regarding the fabrication of such surfaces. So the second part of the proposed project, that of condensation on micro-textured surfaces with patterned wettability to induce the shift from Wenzel (PW) to Cassie State (S) is being delayed. Nonetheless, an important achievement such as the Simultaneous Dropwise/Filmwise Condensation behavior has merged from this collaboration.
I hope I can solve the difficulties regarding the supply of microstructured surfaces.
Nonetheless, thanks to the KAKENHI awarded, a new collaboration with Shanghai Jiao Tong University is taking place. The condensation behavior on superhydrophobic surfaces are the subject of the study. Superhydrophobic surfaces are able to achieve continuous dropwise condensation, which is characteristic of high heat transfer efficiency. In addition, on these novel coalescence-induced droplet-jumping takes place, which offer new vacant surface area for re-nucleation, growth and departure of small droplets.
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| Strategy for Future Research Activity |
Elucidating the effect of micro- and nano-structural defects on superhydrophobic surfaces during condensation phase change. The importance of microstructures on dropwise condensation behavior is being an active subject of durrent research. However research efforts do not difference between the effect of micro- and nano-structures on the droplet shedding mechanism either by gravity or by droplet-jumping. Separating these effects (shedding by gravity versus droplet jumping) is paramount for the successful design of high efficient condensation surfaces.
So far I am addressing the effect of randomly etched microstructures on a copper substrate. However for the fine understanding of the effect of geometry, size and density of the microstructures is paramount. A more controlled and precise fabrication procedure of the microstructures is required. The author is seeking advice in microstructure fabrication which will lead to the complete understanding of micrometer parameters during dropwise condensation heat transfer differentiating from shedding by gravity and/or by coalescence-induced droplet-jumping.
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| Causes of Carryover |
Due to the small nature of the condensing droplets observed on superhydrophobic surfaces (in the order of micrometers) we designed and purchased an optical microscopy setup for the observations of droplets in the micrometer range.
In order to complete the experimental setup, a high-speed CCD camera and an environmental chamber must be built. The effect of non-condensable gases present in ambient air (nitrogen, oxygen and CO2) were found to influence strongly the condensation behavior on hydrophobic and superhydrophobic substrates (Chavan et al. Langmuir 32 (31), pp. 7774-7787, 2016). Hence for the further understanding of the effect of ambient and non-condensable gases, we need to design an environmental chamber on which pressure and the type of gas inside the chamber can be controlled.
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| Expenditure Plan for Carryover Budget |
A CCD area scan camera with high performance and high frame rate will be purchased to complete the optical microscopy setup.
An environmental chamber will also be built and vacuum pump and oxygen and nitrogen gases as utilities will also be purchased.
The applicant will also use part of the money to present the work in the 70th Annual Meeting of the APS (American Physical Society) Division of Fluid Dynamics and in domestic conferences.
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[Journal Article] Heat Transfer through a Condensate Droplet on Hydrophobic and Nanostructured Superhydrophobic Surfaces2016
Author(s)
Shreyas Chavan, Hyeongyun Cha, Daniel Orejon, Kashif Nawaz, Nitish Singla, Yip Fun Yeung, Deokgeun Park, Dong Hoon Kang, Yujin Chang, Yasuyuki Takata, Nenad Miljkovic
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Journal Title
Langmuir
Volume: 32 (31)
Pages: 7774-7787
DOI
Peer Reviewed / Int'l Joint Research
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