TY - JOUR
T1 - Design and Fabrication of a Hybrid Superhydrophobic-Hydrophilic Surface That Exhibits Stable Dropwise Condensation
AU - Mondal, Bikash
AU - Mac Giolla Eain, Marc
AU - Xu, Qian Feng
AU - Egan, Vanessa M.
AU - Punch, Jeff
AU - Lyons, Alan M.
N1 - Publisher Copyright:
© 2015 American Chemical Society.
PY - 2015/10/28
Y1 - 2015/10/28
N2 - Condensation of water vapor is an essential process in power generation, water collection, and thermal management. Dropwise condensation, where condensed droplets are removed from the surface before coalescing into a film, has been shown to increase the heat transfer efficiency and water collection ability of many surfaces. Numerous efforts have been made to create surfaces which can promote dropwise condensation, including superhydrophobic surfaces on which water droplets are highly mobile. However, the challenge with using such surfaces in condensing environments is that hydrophobic coatings can degrade and/or water droplets on superhydrophobic surfaces transition from the mobile Cassie to the wetted Wenzel state over time and condensation shifts to a less-effective filmwise mechanism. To meet the need for a heat-transfer surface that can maintain stable dropwise condensation, we designed and fabricated a hybrid superhydrophobic-hydrophilic surface. An array of hydrophilic needles, thermally connected to a heat sink, was forced through a robust superhydrophobic polymer film. Condensation occurs preferentially on the needle surface due to differences in wettability and temperature. As the droplet grows, the liquid drop on the needle remains in the Cassie state and does not wet the underlying superhydrophobic surface. The water collection rate on this surface was studied using different surface tilt angles, needle array pitch values, and needle heights. Water condensation rates on the hybrid surface were shown to be 4 times greater than for a planar copper surface and twice as large for silanized silicon or superhydrophobic surfaces without hydrophilic features. A convection-conduction heat transfer model was developed; predicted water condensation rates were in good agreement with experimental observations. This type of hybrid superhydrophobic-hydrophilic surface with a larger array of needles is low-cost, robust, and scalable and so could be used for heat transfer and water collection applications.
AB - Condensation of water vapor is an essential process in power generation, water collection, and thermal management. Dropwise condensation, where condensed droplets are removed from the surface before coalescing into a film, has been shown to increase the heat transfer efficiency and water collection ability of many surfaces. Numerous efforts have been made to create surfaces which can promote dropwise condensation, including superhydrophobic surfaces on which water droplets are highly mobile. However, the challenge with using such surfaces in condensing environments is that hydrophobic coatings can degrade and/or water droplets on superhydrophobic surfaces transition from the mobile Cassie to the wetted Wenzel state over time and condensation shifts to a less-effective filmwise mechanism. To meet the need for a heat-transfer surface that can maintain stable dropwise condensation, we designed and fabricated a hybrid superhydrophobic-hydrophilic surface. An array of hydrophilic needles, thermally connected to a heat sink, was forced through a robust superhydrophobic polymer film. Condensation occurs preferentially on the needle surface due to differences in wettability and temperature. As the droplet grows, the liquid drop on the needle remains in the Cassie state and does not wet the underlying superhydrophobic surface. The water collection rate on this surface was studied using different surface tilt angles, needle array pitch values, and needle heights. Water condensation rates on the hybrid surface were shown to be 4 times greater than for a planar copper surface and twice as large for silanized silicon or superhydrophobic surfaces without hydrophilic features. A convection-conduction heat transfer model was developed; predicted water condensation rates were in good agreement with experimental observations. This type of hybrid superhydrophobic-hydrophilic surface with a larger array of needles is low-cost, robust, and scalable and so could be used for heat transfer and water collection applications.
KW - Cassie-Baxter
KW - dropwise condensation
KW - heat transfer
KW - hybrid superhydrophobic-hydrophilic
KW - superhydrophobic surface
KW - water collection
UR - http://www.scopus.com/inward/record.url?scp=84946047119&partnerID=8YFLogxK
U2 - 10.1021/acsami.5b06759
DO - 10.1021/acsami.5b06759
M3 - Article
AN - SCOPUS:84946047119
SN - 1944-8244
VL - 7
SP - 23575
EP - 23588
JO - ACS Applied Materials and Interfaces
JF - ACS Applied Materials and Interfaces
IS - 42
ER -